Source code:
———
The ast module helps Python applications to process trees of the Python abstract syntax grammar. The abstract syntax itself might change with each Python release; this module helps to find out programmatically what the current grammar looks like.
An abstract syntax tree can be generated by passing
as a flag to the
built-in function, or using the
helper provided in this module. The result will be a tree of objects whose classes all inherit from
. An abstract syntax tree can be compiled into a Python code object using the built-in compile() function.
Abstract grammar
The abstract grammar is currently defined as follows:
-- ASDL's 4 builtin types are:-- identifier, int, string, constantmodulePython{mod=Module(stmt* body, type_ignore* type_ignores)|Interactive(stmt* body)|Expression(exprbody)|FunctionType(expr* argtypes, exprreturns)stmt=FunctionDef(identifiername, argumentsargs, stmt* body, expr* decorator_list, expr? returns, string? type_comment, type_param* type_params)|AsyncFunctionDef(identifiername, argumentsargs, stmt* body, expr* decorator_list, expr? returns, string? type_comment, type_param* type_params)|ClassDef(identifiername, expr* bases, keyword* keywords, stmt* body, expr* decorator_list, type_param* type_params)|Return(expr? value)|Delete(expr* targets)|Assign(expr* targets, exprvalue, string? type_comment)|TypeAlias(exprname, type_param* type_params, exprvalue)|AugAssign(exprtarget, operatorop, exprvalue)-- 'simple' indicates that we annotate simple name without parens|AnnAssign(exprtarget, exprannotation, expr? value, intsimple)-- use 'orelse' because else is a keyword in target languages|For(exprtarget, expriter, stmt* body, stmt* orelse, string? type_comment)|AsyncFor(exprtarget, expriter, stmt* body, stmt* orelse, string? type_comment)|While(exprtest, stmt* body, stmt* orelse)|If(exprtest, stmt* body, stmt* orelse)|With(withitem* items, stmt* body, string? type_comment)|AsyncWith(withitem* items, stmt* body, string? type_comment)|Match(exprsubject, match_case* cases)|Raise(expr? exc, expr? cause)|Try(stmt* body, excepthandler* handlers, stmt* orelse, stmt* finalbody)|TryStar(stmt* body, excepthandler* handlers, stmt* orelse, stmt* finalbody)|Assert(exprtest, expr? msg)|Import(alias* names, int? is_lazy)|ImportFrom(identifier? module, alias* names, int? level, int? is_lazy)|Global(identifier* names)|Nonlocal(identifier* names)|Expr(exprvalue)|Pass|Break|Continue-- col_offset is the byte offset in the utf8 string the parser usesattributes(intlineno, intcol_offset, int? end_lineno, int? end_col_offset)-- BoolOp() can use left & right?expr=BoolOp(boolopop, expr* values)|NamedExpr(exprtarget, exprvalue)|BinOp(exprleft, operatorop, exprright)|UnaryOp(unaryopop, exproperand)|Lambda(argumentsargs, exprbody)|IfExp(exprtest, exprbody, exprorelse)|Dict(expr?* keys, expr* values)|Set(expr* elts)|ListComp(exprelt, comprehension* generators)|SetComp(exprelt, comprehension* generators)|DictComp(exprkey, expr? value, comprehension* generators)|GeneratorExp(exprelt, comprehension* generators)-- the grammar constrains where yield expressions can occur|Await(exprvalue)|Yield(expr? value)|YieldFrom(exprvalue)-- need sequences for compare to distinguish between-- x < 4 < 3 and (x < 4) < 3|Compare(exprleft, cmpop* ops, expr* comparators)|Call(exprfunc, expr* args, keyword* keywords)|FormattedValue(exprvalue, intconversion, expr? format_spec)|Interpolation(exprvalue, constantstr, intconversion, expr? format_spec)|JoinedStr(expr* values)|TemplateStr(expr* values)|Constant(constantvalue, string? kind)-- the following expression can appear in assignment context|Attribute(exprvalue, identifierattr, expr_contextctx)|Subscript(exprvalue, exprslice, expr_contextctx)|Starred(exprvalue, expr_contextctx)|Name(identifierid, expr_contextctx)|List(expr* elts, expr_contextctx)|Tuple(expr* elts, expr_contextctx)-- can appear only in Subscript|Slice(expr? lower, expr? upper, expr? step)-- col_offset is the byte offset in the utf8 string the parser usesattributes(intlineno, intcol_offset, int? end_lineno, int? end_col_offset)expr_context=Load|Store|Delboolop=And|Oroperator=Add|Sub|Mult|MatMult|Div|Mod|Pow|LShift|RShift|BitOr|BitXor|BitAnd|FloorDivunaryop=Invert|Not|UAdd|USubcmpop=Eq|NotEq|Lt|LtE|Gt|GtE|Is|IsNot|In|NotIncomprehension=(exprtarget, expriter, expr* ifs, intis_async)excepthandler=ExceptHandler(expr? type, identifier? name, stmt* body)attributes(intlineno, intcol_offset, int? end_lineno, int? end_col_offset)arguments=(arg* posonlyargs, arg* args, arg? vararg, arg* kwonlyargs, expr?* kw_defaults, arg? kwarg, expr* defaults)arg=(identifierarg, expr? annotation, string? type_comment)attributes(intlineno, intcol_offset, int? end_lineno, int? end_col_offset)-- keyword arguments supplied to call (NULL identifier for **kwargs)keyword=(identifier? arg, exprvalue)attributes(intlineno, intcol_offset, int? end_lineno, int? end_col_offset)-- import name with optional 'as' alias.alias=(identifiername, identifier? asname)attributes(intlineno, intcol_offset, int? end_lineno, int? end_col_offset)withitem=(exprcontext_expr, expr? optional_vars)match_case=(patternpattern, expr? guard, stmt* body)pattern=MatchValue(exprvalue)|MatchSingleton(constantvalue)|MatchSequence(pattern* patterns)|MatchMapping(expr* keys, pattern* patterns, identifier? rest)|MatchClass(exprcls, pattern* patterns, identifier* kwd_attrs, pattern* kwd_patterns)|MatchStar(identifier? name)-- The optional "rest" MatchMapping parameter handles capturing extra mapping keys|MatchAs(pattern? pattern, identifier? name)|MatchOr(pattern* patterns)attributes(intlineno, intcol_offset, intend_lineno, intend_col_offset)type_ignore=TypeIgnore(intlineno, stringtag)type_param=TypeVar(identifiername, expr? bound, expr? default_value)|ParamSpec(identifiername, expr? default_value)|TypeVarTuple(identifiername, expr? default_value)attributes(intlineno, intcol_offset, intend_lineno, intend_col_offset)}Node classes
classast.AST
This is the abstract base of all AST node classes. The actual node classes are derived from the Parser/Python.asdl file, which is reproduced
. They are defined in the _ast C module and re-exported in ast.
There is one class defined for each left-hand side symbol in the abstract grammar (for example, ast.stmt or ast.expr). In addition, there is one class defined for each constructor on the right-hand side; these classes inherit from the classes for the left-hand side trees. For example,
inherits from ast.expr. For production rules with alternatives (aka “sums”), the left-hand side class is abstract: only instances of specific constructor nodes are ever created.
_fields
Each concrete class has an attribute _fields which gives the names of all child nodes.
Each instance of a concrete class has one attribute for each child node, of the type as defined in the grammar. For example,
instances have an attribute left of type ast.expr.
If these attributes are marked as optional in the grammar (using a question mark), the value might be None. If the attributes can have zero-or-more values (marked with an asterisk), the values are represented as Python lists. All possible attributes must be present and have valid values when compiling an AST with
.
_field_types
The _field_types attribute on each concrete class is a dictionary mapping field names (as also listed in
) to their types.
>>> ast.TypeVar._field_types{'name': <class 'str'>, 'bound': ast.expr | None, 'default_value': ast.expr | None}Added in version 3.13.
lineno
col_offset
end_lineno
end_col_offset
Instances of ast.expr and ast.stmt subclasses have
,
,
, and
attributes. The lineno and end_lineno are the first and last line numbers of source text span (1-indexed so the first line is line 1) and the col_offset and end_col_offset are the corresponding UTF-8 byte offsets of the first and last tokens that generated the node. The UTF-8 offset is recorded because the parser uses UTF-8 internally.
Note that the end positions are not required by the compiler and are therefore optional. The end offset is after the last symbol, for example one can get the source segment of a one-line expression node using source_line[node.col_offset:node.end_col_offset].
The constructor of a class ast.T parses its arguments as follows:
If there are positional arguments, there must be as many as there are items in T._fields; they will be assigned as attributes of these names.
If there are keyword arguments, they will set the attributes of the same names to the given values.
For example, to create and populate an
node, you could use
node=ast.UnaryOp(ast.USub(),ast.Constant(5,lineno=0,col_offset=0),lineno=0,col_offset=0)If a field that is optional in the grammar is omitted from the constructor, it defaults to None. If a list field is omitted, it defaults to the empty list. If a field of type ast.expr_context is omitted, it defaults to
. If any other field is omitted, a
is raised and the AST node will not have this field. In Python 3.15, this condition will raise an error.
Changed in version 3.8: Class
is now used for all constants.
Changed in version 3.9: Simple indices are represented by their value, extended slices are represented as tuples.
Changed in version 3.13: AST node constructors were changed to provide sensible defaults for omitted fields: optional fields now default to None, list fields default to an empty list, and fields of type ast.expr_context default to
. Previously, omitted attributes would not exist on constructed nodes (accessing them raised
).
Changed in version 3.14: The
output of
nodes includes the values of the node fields.
Deprecated since version 3.8, removed in version 3.14: Previous versions of Python provided the AST classes ast.Num, ast.Str, ast.Bytes, ast.NameConstant and ast.Ellipsis, which were deprecated in Python 3.8. These classes were removed in Python 3.14, and their functionality has been replaced with
.
Deprecated since version 3.9: Old classes ast.Index and ast.ExtSlice are still available, but they will be removed in future Python releases. In the meantime, instantiating them will return an instance of a different class.
Deprecated since version 3.13, removed in version 3.15: Previous versions of Python allowed the creation of AST nodes that were missing required fields. Similarly, AST node constructors allowed arbitrary keyword arguments that were set as attributes of the AST node, even if they did not match any of the fields of the AST node. These cases now raise a
.
Deprecated since version 3.15, will be removed in version 3.20: In the
, the AST node classes that correspond to production rules with variants (aka “sums”) are abstract classes. Previous versions of Python allowed for the creation of direct instances of these abstract node classes. This behavior is deprecated and will be removed in Python 3.20.
Note
The descriptions of the specific node classes displayed here were initially adapted from the fantastic
project and all its contributors.
Root nodes
classast.Module(body, type_ignores)
A Python module, as with
. Node type generated by
in the default "exec"mode.
body is a
of the module’s
.
type_ignores is a
of the module’s type ignore comments; see
for more details.
>>> print(ast.dump(ast.parse('x = 1'),indent=4))Module( body=[ Assign( targets=[ Name(id='x', ctx=Store())], value=Constant(value=1))])classast.Expression(body)
A single Python
. Node type generated by
when mode is "eval".
body is a single node, one of the
.
>>> print(ast.dump(ast.parse('123',mode='eval'),indent=4))Expression( body=Constant(value=123))classast.Interactive(body)
A single
, like in
. Node type generated by
when mode is "single".
body is a
of
.
>>> print(ast.dump(ast.parse('x = 1; y = 2',mode='single'),indent=4))Interactive( body=[ Assign( targets=[ Name(id='x', ctx=Store())], value=Constant(value=1)), Assign( targets=[ Name(id='y', ctx=Store())], value=Constant(value=2))])classast.FunctionType(argtypes, returns)
A representation of an old-style type comments for functions, as Python versions prior to 3.5 didn’t support
annotations. Node type generated by
when mode is "func_type".
Such type comments would look like this:
defsum_two_number(a,b):# type: (int, int) -> intreturna+bargtypes is a
of
.
returns is a single
.
>>> print(ast.dump(ast.parse('(int, str) -> List[int]',mode='func_type'),indent=4))FunctionType( argtypes=[ Name(id='int'), Name(id='str')], returns=Subscript( value=Name(id='List'), slice=Name(id='int')))Added in version 3.8.
Literals
classast.Constant(value, kind)
A constant value. The value attribute of the Constant literal contains the Python object it represents. The values represented can be instances of
,
,
,
,
, and
, and the constants
and
.
The kind attribute is an optional string. For string literals with a u prefix, kind is set to 'u'. For all other constants, kind is None.
>>> print(ast.dump(ast.parse('123',mode='eval'),indent=4))Expression( body=Constant(value=123))>>> print(ast.dump(ast.parse("u'hello'",mode='eval'),indent=4))Expression( body=Constant(value='hello', kind='u'))classast.FormattedValue(value, conversion, format_spec)
Node representing a single formatting field in an f-string. If the string contains a single formatting field and nothing else the node can be isolated otherwise it appears in
.
value is any expression node (such as a literal, a variable, or a function call).
conversion is an integer:
-1: no formatting
97 (ord('a')): !a
formatting
114 (ord('r')): !r
formatting
115 (ord('s')): !s
formatting
format_spec is a
node representing the formatting of the value, or None if no format was specified. Both conversion and format_spec can be set at the same time.
classast.JoinedStr(values)
An f-string, comprising a series of
and
nodes.
>>> print(ast.dump(ast.parse('f"sin({a}) is {sin(a):.3}"',mode='eval'),indent=4))Expression( body=JoinedStr( values=[ Constant(value='sin('), FormattedValue( value=Name(id='a'), conversion=-1), Constant(value=') is '), FormattedValue( value=Call( func=Name(id='sin'), args=[ Name(id='a')]), conversion=-1, format_spec=JoinedStr( values=[ Constant(value='.3')]))]))classast.TemplateStr(values, /)
Added in version 3.14.
Node representing a template string literal, comprising a series of
and
nodes. These nodes may be any order, and do not need to be interleaved.
>>> expr=ast.parse('t"{name} finished {place:ordinal}"',mode='eval')>>> print(ast.dump(expr,indent=4))Expression( body=TemplateStr( values=[ Interpolation( value=Name(id='name'), str='name', conversion=-1), Constant(value=' finished '), Interpolation( value=Name(id='place'), str='place', conversion=-1, format_spec=JoinedStr( values=[ Constant(value='ordinal')]))]))classast.Interpolation(value, str, conversion, format_spec=None)
Added in version 3.14.
Node representing a single interpolation field in a template string literal.
value is any expression node (such as a literal, a variable, or a function call). This has the same meaning as FormattedValue.value.
str is a constant containing the text of the interpolation expression.
If str is set to None, then value is used to generate code when calling
. This no longer guarantees that the generated code is identical to the original and is intended for code generation.
conversion is an integer:
-1: no conversion
97 (ord('a')): !a
conversion
114 (ord('r')): !r
conversion
115 (ord('s')): !s
conversion
This has the same meaning as FormattedValue.conversion.
format_spec is a
node representing the formatting of the value, or None if no format was specified. Both conversion and format_spec can be set at the same time. This has the same meaning as FormattedValue.format_spec.
classast.List(elts, ctx)
classast.Tuple(elts, ctx)
A list or tuple. elts holds a list of nodes representing the elements. ctx is
if the container is an assignment target (i.e. (x,y)=something), and
otherwise.
>>> print(ast.dump(ast.parse('[1, 2, 3]',mode='eval'),indent=4))Expression( body=List( elts=[ Constant(value=1), Constant(value=2), Constant(value=3)]))>>> print(ast.dump(ast.parse('(1, 2, 3)',mode='eval'),indent=4))Expression( body=Tuple( elts=[ Constant(value=1), Constant(value=2), Constant(value=3)]))classast.Set(elts)
A set. elts holds a list of nodes representing the set’s elements.
>>> print(ast.dump(ast.parse('{1, 2, 3}',mode='eval'),indent=4))Expression( body=Set( elts=[ Constant(value=1), Constant(value=2), Constant(value=3)]))classast.Dict(keys, values)
A dictionary. keys and values hold lists of nodes representing the keys and the values respectively, in matching order (what would be returned when calling dictionary.keys() and dictionary.values()).
When doing dictionary unpacking using dictionary literals the expression to be expanded goes in the values list, with a None at the corresponding position in keys.
>>> print(ast.dump(ast.parse('{"a":1, **d}',mode='eval'),indent=4))Expression( body=Dict( keys=[ Constant(value='a'), None], values=[ Constant(value=1), Name(id='d')]))Variables
classast.Name(id, ctx)
A variable name. id holds the name as a string, and ctx is one of the following types.
classast.Load
classast.Store
classast.Del
Variable references can be used to load the value of a variable, to assign a new value to it, or to delete it. Variable references are given a context to distinguish these cases.
>>> print(ast.dump(ast.parse('a'),indent=4))Module( body=[ Expr( value=Name(id='a'))])>>> print(ast.dump(ast.parse('a = 1'),indent=4))Module( body=[ Assign( targets=[ Name(id='a', ctx=Store())], value=Constant(value=1))])>>> print(ast.dump(ast.parse('del a'),indent=4))Module( body=[ Delete( targets=[ Name(id='a', ctx=Del())])])classast.Starred(value, ctx)
A *var variable reference. value holds the variable, typically a
node. This type must be used when building a
node with *args.
>>> print(ast.dump(ast.parse('a, *b = it'),indent=4))Module( body=[ Assign( targets=[ Tuple( elts=[ Name(id='a', ctx=Store()), Starred( value=Name(id='b', ctx=Store()), ctx=Store())], ctx=Store())], value=Name(id='it'))])Expressions
classast.Expr(value)
When an expression, such as a function call, appears as a statement by itself with its return value not used or stored, it is wrapped in this container. value holds one of the other nodes in this section, a
, a
, a
, a
or
node.
>>> print(ast.dump(ast.parse('-a'),indent=4))Module( body=[ Expr( value=UnaryOp( op=USub(), operand=Name(id='a')))])classast.UnaryOp(op, operand)
A unary operation. op is the operator, and operand any expression node.
classast.UAdd
classast.USub
classast.Not
classast.Invert
Unary operator tokens. Not is the not keyword, Invert is the ~ operator.
>>> print(ast.dump(ast.parse('not x',mode='eval'),indent=4))Expression( body=UnaryOp( op=Not(), operand=Name(id='x')))classast.BinOp(left, op, right)
A binary operation (like addition or division). op is the operator, and left and right are any expression nodes.
>>> print(ast.dump(ast.parse('x + y',mode='eval'),indent=4))Expression( body=BinOp( left=Name(id='x'), op=Add(), right=Name(id='y')))classast.Add
classast.Sub
classast.Mult
classast.Div
classast.FloorDiv
classast.Mod
classast.Pow
classast.LShift
classast.RShift
classast.BitOr
classast.BitXor
classast.BitAnd
classast.MatMult
Binary operator tokens.
classast.BoolOp(op, values)
A boolean operation, ‘or’ or ‘and’. op is
or
. values are the values involved. Consecutive operations with the same operator, such as aorborc, are collapsed into one node with several values.
This doesn’t include not, which is a
.
>>> print(ast.dump(ast.parse('x or y',mode='eval'),indent=4))Expression( body=BoolOp( op=Or(), values=[ Name(id='x'), Name(id='y')]))classast.And
classast.Or
Boolean operator tokens.
classast.Compare(left, ops, comparators)
A comparison of two or more values. left is the first value in the comparison, ops the list of operators, and comparators the list of values after the first element in the comparison.
>>> print(ast.dump(ast.parse('1 <= a < 10',mode='eval'),indent=4))Expression( body=Compare( left=Constant(value=1), ops=[ LtE(), Lt()], comparators=[ Name(id='a'), Constant(value=10)]))classast.Eq
classast.NotEq
classast.Lt
classast.LtE
classast.Gt
classast.GtE
classast.Is
classast.IsNot
classast.In
classast.NotIn
Comparison operator tokens.
classast.Call(func, args, keywords)
A function call. func is the function, which will often be a
or
object. Of the arguments:
args holds a list of the arguments passed by position.
keywords holds a list of
objects representing arguments passed by keyword.
The args and keywords arguments are optional and default to empty lists.
>>> print(ast.dump(ast.parse('func(a, b=c, *d, **e)',mode='eval'),indent=4))Expression( body=Call( func=Name(id='func'), args=[ Name(id='a'), Starred( value=Name(id='d'))], keywords=[ keyword( arg='b', value=Name(id='c')), keyword( value=Name(id='e'))]))classast.keyword(arg, value)
A keyword argument to a function call or class definition. arg is a raw string of the parameter name, value is a node to pass in.
classast.IfExp(test, body, orelse)
An expression such as aifbelsec. Each field holds a single node, so in the following example, all three are
nodes.
>>> print(ast.dump(ast.parse('a if b else c',mode='eval'),indent=4))Expression( body=IfExp( test=Name(id='b'), body=Name(id='a'), orelse=Name(id='c')))classast.Attribute(value, attr, ctx)
Attribute access, e.g. d.keys. value is a node, typically a
. attr is a bare string giving the name of the attribute, and ctx is
,
or
according to how the attribute is acted on.
>>> print(ast.dump(ast.parse('snake.colour',mode='eval'),indent=4))Expression( body=Attribute( value=Name(id='snake'), attr='colour'))classast.NamedExpr(target, value)
A named expression. This AST node is produced by the assignment expressions operator (also known as the walrus operator). As opposed to the
node in which the first argument can be multiple nodes, in this case both target and value must be single nodes.
>>> print(ast.dump(ast.parse('(x := 4)',mode='eval'),indent=4))Expression( body=NamedExpr( target=Name(id='x', ctx=Store()), value=Constant(value=4)))Added in version 3.8.
Subscripting
classast.Subscript(value, slice, ctx)
A subscript, such as l[1]. value is the subscripted object (usually sequence or mapping). slice is an index, slice or key. It can be a
and contain a
. ctx is
,
or
according to the action performed with the subscript.
>>> print(ast.dump(ast.parse('l[1:2, 3]',mode='eval'),indent=4))Expression( body=Subscript( value=Name(id='l'), slice=Tuple( elts=[ Slice( lower=Constant(value=1), upper=Constant(value=2)), Constant(value=3)])))classast.Slice(lower, upper, step)
Regular slicing (on the form lower:upper or lower:upper:step). Can occur only inside the slice field of
, either directly or as an element of
.
>>> print(ast.dump(ast.parse('l[1:2]',mode='eval'),indent=4))Expression( body=Subscript( value=Name(id='l'), slice=Slice( lower=Constant(value=1), upper=Constant(value=2))))Comprehensions
classast.ListComp(elt, generators)
classast.SetComp(elt, generators)
classast.GeneratorExp(elt, generators)
classast.DictComp(key, value, generators)
List and set comprehensions, generator expressions, and dictionary comprehensions. elt (or key and value) is a single node representing the part that will be evaluated for each item.
For dictionary comprehensions using unpacking, for example {**itemforiteminitems}, the expression to be expanded goes in key and value is None.
generators is a list of
nodes.
>>> print(ast.dump(... ast.parse('[x for x in numbers]',mode='eval'),... indent=4,... ))Expression( body=ListComp( elt=Name(id='x'), generators=[ comprehension( target=Name(id='x', ctx=Store()), iter=Name(id='numbers'), is_async=0)]))>>> print(ast.dump(... ast.parse('{x: x**2 for x in numbers}',mode='eval'),... indent=4,... ))Expression( body=DictComp( key=Name(id='x'), value=BinOp( left=Name(id='x'), op=Pow(), right=Constant(value=2)), generators=[ comprehension( target=Name(id='x', ctx=Store()), iter=Name(id='numbers'), is_async=0)]))>>> print(ast.dump(... ast.parse('{x for x in numbers}',mode='eval'),... indent=4,... ))Expression( body=SetComp( elt=Name(id='x'), generators=[ comprehension( target=Name(id='x', ctx=Store()), iter=Name(id='numbers'), is_async=0)]))classast.comprehension(target, iter, ifs, is_async)
One for clause in a comprehension. target is the reference to use for each element - typically a
or
node. iter is the object to iterate over. ifs is a list of test expressions: each for clause can have multiple ifs.
is_async indicates a comprehension is asynchronous (using an asyncfor instead of for). The value is an integer (0 or 1).
>>> print(ast.dump(ast.parse('[ord(c) for line in file for c in line]',mode='eval'),... indent=4))# Multiple comprehensions in one.Expression( body=ListComp( elt=Call( func=Name(id='ord'), args=[ Name(id='c')]), generators=[ comprehension( target=Name(id='line', ctx=Store()), iter=Name(id='file'), is_async=0), comprehension( target=Name(id='c', ctx=Store()), iter=Name(id='line'), is_async=0)]))>>> print(ast.dump(ast.parse('(n**2 for n in it if n>5 if n<10)',mode='eval'),... indent=4))# generator comprehensionExpression( body=GeneratorExp( elt=BinOp( left=Name(id='n'), op=Pow(), right=Constant(value=2)), generators=[ comprehension( target=Name(id='n', ctx=Store()), iter=Name(id='it'), ifs=[ Compare( left=Name(id='n'), ops=[ Gt()], comparators=[ Constant(value=5)]), Compare( left=Name(id='n'), ops=[ Lt()], comparators=[ Constant(value=10)])], is_async=0)]))>>> print(ast.dump(ast.parse('[i async for i in soc]',mode='eval'),... indent=4))# Async comprehensionExpression( body=ListComp( elt=Name(id='i'), generators=[ comprehension( target=Name(id='i', ctx=Store()), iter=Name(id='soc'), is_async=1)]))Statements
classast.Assign(targets, value, type_comment)
An assignment. targets is a list of nodes, and value is a single node.
Multiple nodes in targets represents assigning the same value to each. Unpacking is represented by putting a
or
within targets.
type_comment is an optional string with the type annotation as a comment.
>>> print(ast.dump(ast.parse('a = b = 1'),indent=4))# Multiple assignmentModule( body=[ Assign( targets=[ Name(id='a', ctx=Store()), Name(id='b', ctx=Store())], value=Constant(value=1))])>>> print(ast.dump(ast.parse('a,b = c'),indent=4))# UnpackingModule( body=[ Assign( targets=[ Tuple( elts=[ Name(id='a', ctx=Store()), Name(id='b', ctx=Store())], ctx=Store())], value=Name(id='c'))])classast.AnnAssign(target, annotation, value, simple)
An assignment with a type annotation. target is a single node and can be a
, an
or a
. annotation is the annotation, such as a
or Name node. value is a single optional node.
simple is always either 0 (indicating a “complex” target) or 1 (indicating a “simple” target). A “simple” target consists solely of a
node that does not appear between parentheses; all other targets are considered complex. Only simple targets appear in the
dictionary of modules and classes.
>>> print(ast.dump(ast.parse('c: int'),indent=4))Module( body=[ AnnAssign( target=Name(id='c', ctx=Store()), annotation=Name(id='int'), simple=1)])>>> print(ast.dump(ast.parse('(a): int = 1'),indent=4))# Annotation with parenthesisModule( body=[ AnnAssign( target=Name(id='a', ctx=Store()), annotation=Name(id='int'), value=Constant(value=1), simple=0)])>>> print(ast.dump(ast.parse('a.b: int'),indent=4))# Attribute annotationModule( body=[ AnnAssign( target=Attribute( value=Name(id='a'), attr='b', ctx=Store()), annotation=Name(id='int'), simple=0)])>>> print(ast.dump(ast.parse('a[1]: int'),indent=4))# Subscript annotationModule( body=[ AnnAssign( target=Subscript( value=Name(id='a'), slice=Constant(value=1), ctx=Store()), annotation=Name(id='int'), simple=0)])classast.AugAssign(target, op, value)
Augmented assignment, such as a+=1. In the following example, target is a
node for x (with the
context), op is
, and value is a
with value for 1.
The target attribute cannot be of class
or
, unlike the targets of
.
>>> print(ast.dump(ast.parse('x += 2'),indent=4))Module( body=[ AugAssign( target=Name(id='x', ctx=Store()), op=Add(), value=Constant(value=2))])classast.Raise(exc, cause)
A raise statement. exc is the exception object to be raised, normally a
or
, or None for a standalone raise. cause is the optional part for y in raisexfromy.
>>> print(ast.dump(ast.parse('raise x from y'),indent=4))Module( body=[ Raise( exc=Name(id='x'), cause=Name(id='y'))])classast.Assert(test, msg)
An assertion. test holds the condition, such as a
node. msg holds the failure message.
>>> print(ast.dump(ast.parse('assert x,y'),indent=4))Module( body=[ Assert( test=Name(id='x'), msg=Name(id='y'))])classast.Delete(targets)
Represents a del statement. targets is a list of nodes, such as
,
or
nodes.
>>> print(ast.dump(ast.parse('del x,y,z'),indent=4))Module( body=[ Delete( targets=[ Name(id='x', ctx=Del()), Name(id='y', ctx=Del()), Name(id='z', ctx=Del())])])classast.Pass
A pass statement.
>>> print(ast.dump(ast.parse('pass'),indent=4))Module( body=[ Pass()])classast.TypeAlias(name, type_params, value)
A
created through the
statement. name is the name of the alias, type_params is a list of
, and value is the value of the type alias.
>>> print(ast.dump(ast.parse('type Alias = int'),indent=4))Module( body=[ TypeAlias( name=Name(id='Alias', ctx=Store()), value=Name(id='int'))])Added in version 3.12.
Other statements which are only applicable inside functions or loops are described in other sections.
Imports
classast.Import(names)
An import statement. names is a list of
nodes.
>>> print(ast.dump(ast.parse('import x,y,z'),indent=4))Module( body=[ Import( names=[ alias(name='x'), alias(name='y'), alias(name='z')], is_lazy=0)])classast.ImportFrom(module, names, level)
Represents fromximporty. module is a raw string of the ‘from’ name, without any leading dots, or None for statements such as from.importfoo. level is an integer holding the level of the relative import (0 means absolute import).
>>> print(ast.dump(ast.parse('from y import x,y,z'),indent=4))Module( body=[ ImportFrom( module='y', names=[ alias(name='x'), alias(name='y'), alias(name='z')], level=0, is_lazy=0)])classast.alias(name, asname)
Both parameters are raw strings of the names. asname can be None if the regular name is to be used.
>>> print(ast.dump(ast.parse('from ..foo.bar import a as b, c'),indent=4))Module( body=[ ImportFrom( module='foo.bar', names=[ alias(name='a', asname='b'), alias(name='c')], level=2, is_lazy=0)])Control flow
Note
Optional clauses such as else are stored as an empty list if they’re not present.
classast.If(test, body, orelse)
An if statement. test holds a single node, such as a
node. body and orelse each hold a list of nodes.
elif clauses don’t have a special representation in the AST, but rather appear as extra If nodes within the orelse section of the previous one.
>>> print(ast.dump(ast.parse("""... if x:... ...... elif y:... ...... else:... ...... """),indent=4))Module( body=[ If( test=Name(id='x'), body=[ Expr( value=Constant(value=Ellipsis))], orelse=[ If( test=Name(id='y'), body=[ Expr( value=Constant(value=Ellipsis))], orelse=[ Expr( value=Constant(value=Ellipsis))])])])classast.For(target, iter, body, orelse, type_comment)
A for loop. target holds the variable(s) the loop assigns to, as a single
,
,
,
or
node. iter holds the item to be looped over, again as a single node. body and orelse contain lists of nodes to execute. Those in orelse are executed if the loop finishes normally, rather than via a break statement.
type_comment is an optional string with the type annotation as a comment.
>>> print(ast.dump(ast.parse("""... for x in y:... ...... else:... ...... """),indent=4))Module( body=[ For( target=Name(id='x', ctx=Store()), iter=Name(id='y'), body=[ Expr( value=Constant(value=Ellipsis))], orelse=[ Expr( value=Constant(value=Ellipsis))])])classast.While(test, body, orelse)
A while loop. test holds the condition, such as a
node.
>>> print(ast.dump(ast.parse("""... while x:... ...... else:... ...... """),indent=4))Module( body=[ While( test=Name(id='x'), body=[ Expr( value=Constant(value=Ellipsis))], orelse=[ Expr( value=Constant(value=Ellipsis))])])classast.Break
classast.Continue
The break and continue statements.
>>> print(ast.dump(ast.parse("""\... for a in b:... if a > 5:... break... else:... continue...... """),indent=4))Module( body=[ For( target=Name(id='a', ctx=Store()), iter=Name(id='b'), body=[ If( test=Compare( left=Name(id='a'), ops=[ Gt()], comparators=[ Constant(value=5)]), body=[ Break()], orelse=[ Continue()])])])classast.Try(body, handlers, orelse, finalbody)
try blocks. All attributes are list of nodes to execute, except for handlers, which is a list of
nodes.
>>> print(ast.dump(ast.parse("""... try:... ...... except Exception:... ...... except OtherException as e:... ...... else:... ...... finally:... ...... """),indent=4))Module( body=[ Try( body=[ Expr( value=Constant(value=Ellipsis))], handlers=[ ExceptHandler( type=Name(id='Exception'), body=[ Expr( value=Constant(value=Ellipsis))]), ExceptHandler( type=Name(id='OtherException'), name='e', body=[ Expr( value=Constant(value=Ellipsis))])], orelse=[ Expr( value=Constant(value=Ellipsis))], finalbody=[ Expr( value=Constant(value=Ellipsis))])])classast.TryStar(body, handlers, orelse, finalbody)
try blocks which are followed by except* clauses. The attributes are the same as for
but the
nodes in handlers are interpreted as except* blocks rather than except.
>>> print(ast.dump(ast.parse("""... try:... ...... except* Exception:... ...... """),indent=4))Module( body=[ TryStar( body=[ Expr( value=Constant(value=Ellipsis))], handlers=[ ExceptHandler( type=Name(id='Exception'), body=[ Expr( value=Constant(value=Ellipsis))])])])Added in version 3.11.
classast.ExceptHandler(type, name, body)
A single except clause. type is the exception type it will match, typically a
node (or None for a catch-all except: clause). name is a raw string for the name to hold the exception, or None if the clause doesn’t have asfoo. body is a list of nodes.
>>> print(ast.dump(ast.parse("""\... try:... a + 1... except TypeError:... pass... """),indent=4))Module( body=[ Try( body=[ Expr( value=BinOp( left=Name(id='a'), op=Add(), right=Constant(value=1)))], handlers=[ ExceptHandler( type=Name(id='TypeError'), body=[ Pass()])])])classast.With(items, body, type_comment)
A with block. items is a list of
nodes representing the context managers, and body is the indented block inside the context.
type_comment is an optional string with the type annotation as a comment.
classast.withitem(context_expr, optional_vars)
A single context manager in a with block. context_expr is the context manager, often a
node. optional_vars is a
,
or
for the asfoo part, or None if that isn’t used.
>>> print(ast.dump(ast.parse("""\... with a as b, c as d:... something(b, d)... """),indent=4))Module( body=[ With( items=[ withitem( context_expr=Name(id='a'), optional_vars=Name(id='b', ctx=Store())), withitem( context_expr=Name(id='c'), optional_vars=Name(id='d', ctx=Store()))], body=[ Expr( value=Call( func=Name(id='something'), args=[ Name(id='b'), Name(id='d')]))])])Pattern matching
classast.Match(subject, cases)
A match statement. subject holds the subject of the match (the object that is being matched against the cases) and cases contains an iterable of
nodes with the different cases.
Added in version 3.10.
classast.match_case(pattern, guard, body)
A single case pattern in a match statement. pattern contains the match pattern that the subject will be matched against. Note that the
nodes produced for patterns differ from those produced for expressions, even when they share the same syntax.
The guard attribute contains an expression that will be evaluated if the pattern matches the subject.
body contains a list of nodes to execute if the pattern matches and the result of evaluating the guard expression is true.
>>> print(ast.dump(ast.parse("""... match x:... case [x] if x>0:... ...... case tuple():... ...... """),indent=4))Module( body=[ Match( subject=Name(id='x'), cases=[ match_case( pattern=MatchSequence( patterns=[ MatchAs(name='x')]), guard=Compare( left=Name(id='x'), ops=[ Gt()], comparators=[ Constant(value=0)]), body=[ Expr( value=Constant(value=Ellipsis))]), match_case( pattern=MatchClass( cls=Name(id='tuple')), body=[ Expr( value=Constant(value=Ellipsis))])])])Added in version 3.10.
classast.MatchValue(value)
A match literal or value pattern that compares by equality. value is an expression node. Permitted value nodes are restricted as described in the match statement documentation. This pattern succeeds if the match subject is equal to the evaluated value.
>>> print(ast.dump(ast.parse("""... match x:... case "Relevant":... ...... """),indent=4))Module( body=[ Match( subject=Name(id='x'), cases=[ match_case( pattern=MatchValue( value=Constant(value='Relevant')), body=[ Expr( value=Constant(value=Ellipsis))])])])Added in version 3.10.
classast.MatchSingleton(value)
A match literal pattern that compares by identity. value is the singleton to be compared against: None, True, or False. This pattern succeeds if the match subject is the given constant.
>>> print(ast.dump(ast.parse("""... match x:... case None:... ...... """),indent=4))Module( body=[ Match( subject=Name(id='x'), cases=[ match_case( pattern=MatchSingleton(value=None), body=[ Expr( value=Constant(value=Ellipsis))])])])Added in version 3.10.
classast.MatchSequence(patterns)
A match sequence pattern. patterns contains the patterns to be matched against the subject elements if the subject is a sequence. Matches a variable length sequence if one of the subpatterns is a MatchStar node, otherwise matches a fixed length sequence.
>>> print(ast.dump(ast.parse("""... match x:... case [1, 2]:... ...... """),indent=4))Module( body=[ Match( subject=Name(id='x'), cases=[ match_case( pattern=MatchSequence( patterns=[ MatchValue( value=Constant(value=1)), MatchValue( value=Constant(value=2))]), body=[ Expr( value=Constant(value=Ellipsis))])])])Added in version 3.10.
classast.MatchStar(name)
Matches the rest of the sequence in a variable length match sequence pattern. If name is not None, a list containing the remaining sequence elements is bound to that name if the overall sequence pattern is successful.
>>> print(ast.dump(ast.parse("""... match x:... case [1, 2, *rest]:... ...... case [*_]:... ...... """),indent=4))Module( body=[ Match( subject=Name(id='x'), cases=[ match_case( pattern=MatchSequence( patterns=[ MatchValue( value=Constant(value=1)), MatchValue( value=Constant(value=2)), MatchStar(name='rest')]), body=[ Expr( value=Constant(value=Ellipsis))]), match_case( pattern=MatchSequence( patterns=[ MatchStar()]), body=[ Expr( value=Constant(value=Ellipsis))])])])Added in version 3.10.
classast.MatchMapping(keys, patterns, rest)
A match mapping pattern. keys is a sequence of expression nodes. patterns is a corresponding sequence of pattern nodes. rest is an optional name that can be specified to capture the remaining mapping elements. Permitted key expressions are restricted as described in the match statement documentation.
This pattern succeeds if the subject is a mapping, all evaluated key expressions are present in the mapping, and the value corresponding to each key matches the corresponding subpattern. If rest is not None, a dict containing the remaining mapping elements is bound to that name if the overall mapping pattern is successful.
>>> print(ast.dump(ast.parse("""... match x:... case {1: _, 2: _}:... ...... case {**rest}:... ...... """),indent=4))Module( body=[ Match( subject=Name(id='x'), cases=[ match_case( pattern=MatchMapping( keys=[ Constant(value=1), Constant(value=2)], patterns=[ MatchAs(), MatchAs()]), body=[ Expr( value=Constant(value=Ellipsis))]), match_case( pattern=MatchMapping(rest='rest'), body=[ Expr( value=Constant(value=Ellipsis))])])])Added in version 3.10.
classast.MatchClass(cls, patterns, kwd_attrs, kwd_patterns)
A match class pattern. cls is an expression giving the nominal class to be matched. patterns is a sequence of pattern nodes to be matched against the class defined sequence of pattern matching attributes. kwd_attrs is a sequence of additional attributes to be matched (specified as keyword arguments in the class pattern), kwd_patterns are the corresponding patterns (specified as keyword values in the class pattern).
This pattern succeeds if the subject is an instance of the nominated class, all positional patterns match the corresponding class-defined attributes, and any specified keyword attributes match their corresponding pattern.
Note: classes may define a property that returns self in order to match a pattern node against the instance being matched. Several builtin types are also matched that way, as described in the match statement documentation.
>>> print(ast.dump(ast.parse("""... match x:... case Point2D(0, 0):... ...... case Point3D(x=0, y=0, z=0):... ...... """),indent=4))Module( body=[ Match( subject=Name(id='x'), cases=[ match_case( pattern=MatchClass( cls=Name(id='Point2D'), patterns=[ MatchValue( value=Constant(value=0)), MatchValue( value=Constant(value=0))]), body=[ Expr( value=Constant(value=Ellipsis))]), match_case( pattern=MatchClass( cls=Name(id='Point3D'), kwd_attrs=[ 'x', 'y', 'z'], kwd_patterns=[ MatchValue( value=Constant(value=0)), MatchValue( value=Constant(value=0)), MatchValue( value=Constant(value=0))]), body=[ Expr( value=Constant(value=Ellipsis))])])])Added in version 3.10.
classast.MatchAs(pattern, name)
A match “as-pattern”, capture pattern or wildcard pattern. pattern contains the match pattern that the subject will be matched against. If the pattern is None, the node represents a capture pattern (i.e a bare name) and will always succeed.
The name attribute contains the name that will be bound if the pattern is successful. If name is None, pattern must also be None and the node represents the wildcard pattern.
>>> print(ast.dump(ast.parse("""... match x:... case [x] as y:... ...... case _:... ...... """),indent=4))Module( body=[ Match( subject=Name(id='x'), cases=[ match_case( pattern=MatchAs( pattern=MatchSequence( patterns=[ MatchAs(name='x')]), name='y'), body=[ Expr( value=Constant(value=Ellipsis))]), match_case( pattern=MatchAs(), body=[ Expr( value=Constant(value=Ellipsis))])])])Added in version 3.10.
classast.MatchOr(patterns)
A match “or-pattern”. An or-pattern matches each of its subpatterns in turn to the subject, until one succeeds. The or-pattern is then deemed to succeed. If none of the subpatterns succeed the or-pattern fails. The patterns attribute contains a list of match pattern nodes that will be matched against the subject.
>>> print(ast.dump(ast.parse("""... match x:... case [x] | (y):... ...... """),indent=4))Module( body=[ Match( subject=Name(id='x'), cases=[ match_case( pattern=MatchOr( patterns=[ MatchSequence( patterns=[ MatchAs(name='x')]), MatchAs(name='y')]), body=[ Expr( value=Constant(value=Ellipsis))])])])Added in version 3.10.
Type annotations
classast.TypeIgnore(lineno, tag)
A #type:ignore comment located at lineno. tag is the optional tag specified by the form #type:ignore<tag>.
>>> print(ast.dump(ast.parse('x = 1 # type: ignore',type_comments=True),indent=4))Module( body=[ Assign( targets=[ Name(id='x', ctx=Store())], value=Constant(value=1))], type_ignores=[ TypeIgnore(lineno=1, tag='')])>>> print(ast.dump(ast.parse('x: bool = 1 # type: ignore[assignment]',type_comments=True),indent=4))Module( body=[ AnnAssign( target=Name(id='x', ctx=Store()), annotation=Name(id='bool'), value=Constant(value=1), simple=1)], type_ignores=[ TypeIgnore(lineno=1, tag='[assignment]')])Note
TypeIgnore nodes are not generated when the type_comments parameter is set to False (default). See
for more details.
Added in version 3.8.
Type parameters
can exist on classes, functions, and type aliases.
classast.TypeVar(name, bound, default_value)
A
. name is the name of the type variable. bound is the bound or constraints, if any. If bound is a
, it represents constraints; otherwise it represents the bound. default_value is the default value; if the TypeVar has no default, this attribute will be set to None.
>>> print(ast.dump(ast.parse("type Alias[T: int = bool] = list[T]"),indent=4))Module( body=[ TypeAlias( name=Name(id='Alias', ctx=Store()), type_params=[ TypeVar( name='T', bound=Name(id='int'), default_value=Name(id='bool'))], value=Subscript( value=Name(id='list'), slice=Name(id='T')))])Added in version 3.12.
Changed in version 3.13: Added the default_value parameter.
classast.ParamSpec(name, default_value)
A
. name is the name of the parameter specification. default_value is the default value; if the ParamSpec has no default, this attribute will be set to None.
>>> print(ast.dump(ast.parse("type Alias[**P = [int, str]] = Callable[P, int]"),indent=4))Module( body=[ TypeAlias( name=Name(id='Alias', ctx=Store()), type_params=[ ParamSpec( name='P', default_value=List( elts=[ Name(id='int'), Name(id='str')]))], value=Subscript( value=Name(id='Callable'), slice=Tuple( elts=[ Name(id='P'), Name(id='int')])))])Added in version 3.12.
Changed in version 3.13: Added the default_value parameter.
classast.TypeVarTuple(name, default_value)
A
. name is the name of the type variable tuple. default_value is the default value; if the TypeVarTuple has no default, this attribute will be set to None.
>>> print(ast.dump(ast.parse("type Alias[*Ts = ()] = tuple[*Ts]"),indent=4))Module( body=[ TypeAlias( name=Name(id='Alias', ctx=Store()), type_params=[ TypeVarTuple(name='Ts', default_value=Tuple())], value=Subscript( value=Name(id='tuple'), slice=Tuple( elts=[ Starred( value=Name(id='Ts'))])))])Added in version 3.12.
Changed in version 3.13: Added the default_value parameter.
Function and class definitions
classast.FunctionDef(name, args, body, decorator_list, returns, type_comment, type_params)
A function definition.
name is a raw string of the function name.
args is an
node.
body is the list of nodes inside the function.
decorator_list is the list of decorators to be applied, stored outermost first (i.e. the first in the list will be applied last).
returns is the return annotation.
type_params is a list of
.
type_comment is an optional string with the type annotation as a comment.
Changed in version 3.12: Added type_params.
classast.Lambda(args, body)
lambda is a minimal function definition that can be used inside an expression. Unlike
, body holds a single node.
>>> print(ast.dump(ast.parse('lambda x,y: ...'),indent=4))Module( body=[ Expr( value=Lambda( args=arguments( args=[ arg(arg='x'), arg(arg='y')]), body=Constant(value=Ellipsis)))])classast.arguments(posonlyargs, args, vararg, kwonlyargs, kw_defaults, kwarg, defaults)
The arguments for a function.
posonlyargs, args and kwonlyargs are lists of
nodes.
vararg and kwarg are single
nodes, referring to the *args,**kwargs parameters.
kw_defaults is a list of default values for keyword-only arguments. If one is None, the corresponding argument is required.
defaults is a list of default values for arguments that can be passed positionally. If there are fewer defaults, they correspond to the last n arguments.
classast.arg(arg, annotation, type_comment)
A single argument in a list. arg is a raw string of the argument name; annotation is its annotation, such as a
node.
type_comment is an optional string with the type annotation as a comment
>>> print(ast.dump(ast.parse("""\... @decorator1... @decorator2... def f(a: 'annotation', b=1, c=2, *d, e, f=3, **g) -> 'return annotation':... pass... """),indent=4))Module( body=[ FunctionDef( name='f', args=arguments( args=[ arg( arg='a', annotation=Constant(value='annotation')), arg(arg='b'), arg(arg='c')], vararg=arg(arg='d'), kwonlyargs=[ arg(arg='e'), arg(arg='f')], kw_defaults=[ None, Constant(value=3)], kwarg=arg(arg='g'), defaults=[ Constant(value=1), Constant(value=2)]), body=[ Pass()], decorator_list=[ Name(id='decorator1'), Name(id='decorator2')], returns=Constant(value='return annotation'))])classast.Return(value)
A return statement.
>>> print(ast.dump(ast.parse('return 4'),indent=4))Module( body=[ Return( value=Constant(value=4))])classast.Yield(value)
classast.YieldFrom(value)
A yield or yieldfrom expression. Because these are expressions, they must be wrapped in an
node if the value sent back is not used.
>>> print(ast.dump(ast.parse('yield x'),indent=4))Module( body=[ Expr( value=Yield( value=Name(id='x')))])>>> print(ast.dump(ast.parse('yield from x'),indent=4))Module( body=[ Expr( value=YieldFrom( value=Name(id='x')))])classast.Global(names)
classast.Nonlocal(names)
global and nonlocal statements. names is a list of raw strings.
>>> print(ast.dump(ast.parse('global x,y,z'),indent=4))Module( body=[ Global( names=[ 'x', 'y', 'z'])])>>> print(ast.dump(ast.parse('nonlocal x,y,z'),indent=4))Module( body=[ Nonlocal( names=[ 'x', 'y', 'z'])])classast.ClassDef(name, bases, keywords, body, decorator_list, type_params)
A class definition.
name is a raw string for the class name
bases is a list of nodes for explicitly specified base classes.
keywords is a list of
nodes, principally for ‘metaclass’. Other keywords will be passed to the metaclass, as per
.
body is a list of nodes representing the code within the class definition.
decorator_list is a list of nodes, as in
.
type_params is a list of
.
>>> print(ast.dump(ast.parse("""\... @decorator1... @decorator2... class Foo(base1, base2, metaclass=meta):... pass... """),indent=4))Module( body=[ ClassDef( name='Foo', bases=[ Name(id='base1'), Name(id='base2')], keywords=[ keyword( arg='metaclass', value=Name(id='meta'))], body=[ Pass()], decorator_list=[ Name(id='decorator1'), Name(id='decorator2')])])Changed in version 3.12: Added type_params.
Async and await
classast.AsyncFunctionDef(name, args, body, decorator_list, returns, type_comment, type_params)
An asyncdef function definition. Has the same fields as
.
Changed in version 3.12: Added type_params.
classast.Await(value)
An await expression. value is what it waits for. Only valid in the body of an
.
>>> print(ast.dump(ast.parse("""\... async def f():... await other_func()... """),indent=4))Module( body=[ AsyncFunctionDef( name='f', args=arguments(), body=[ Expr( value=Await( value=Call( func=Name(id='other_func'))))])])classast.AsyncFor(target, iter, body, orelse, type_comment)
classast.AsyncWith(items, body, type_comment)
asyncfor loops and asyncwith context managers. They have the same fields as
and
, respectively. Only valid in the body of an
.
Note
When a string is parsed by
, operator nodes (subclasses of ast.operator, ast.unaryop, ast.cmpop, ast.boolop and ast.expr_context) on the returned tree will be singletons. Changes to one will be reflected in all other occurrences of the same value (for example,
).
ast helpers
Apart from the node classes, the ast module defines these utility functions and classes for traversing abstract syntax trees:
ast.parse(source, filename='<unknown>', mode='exec', *, type_comments=False, feature_version=None, optimize=-1, module=None)
Parse the source into an AST node. Equivalent to compile(source,filename,mode,flags=FLAGS_VALUE,optimize=optimize,module=module), where FLAGS_VALUE is ast.PyCF_ONLY_AST if optimize<=0 and ast.PyCF_OPTIMIZED_AST otherwise.
If type_comments=True is given, the parser is modified to check and return type comments as specified by
and
. This is equivalent to adding
to the flags passed to
. This will report syntax errors for misplaced type comments. Without this flag, type comments will be ignored, and the type_comment field on selected AST nodes will always be None. In addition, the locations of #type:ignore comments will be returned as the type_ignores attribute of
(otherwise it is always an empty list).
In addition, if mode is 'func_type', the input syntax is modified to correspond to
“signature type comments”, for example (str,int)->List[str].
Setting feature_version to a tuple (major,minor) will result in a “best-effort” attempt to parse using that Python version’s grammar. For example, setting feature_version=(3,9) will attempt to disallow parsing of
statements. Currently major must equal to 3. The lowest supported version is (3,7) (and this may increase in future Python versions); the highest is sys.version_info[0:2]. “Best-effort” attempt means there is no guarantee that the parse (or success of the parse) is the same as when run on the Python version corresponding to feature_version.
If source contains a null character (\0),
is raised.
Warning
Note that successfully parsing source code into an AST object doesn’t guarantee that the source code provided is valid Python code that can be executed as the compilation step can raise further
exceptions. For instance, the source return42 generates a valid AST node for a return statement, but it cannot be compiled alone (it needs to be inside a function node).
In particular, ast.parse() won’t do any scoping checks, which the compilation step does.
Warning
It is possible to crash the Python interpreter with a sufficiently large/complex string due to stack depth limitations in Python’s AST compiler.
Changed in version 3.8: Added type_comments, mode='func_type' and feature_version.
Changed in version 3.13: The minimum supported version for feature_version is now (3,7). The optimize argument was added.
Added in version 3.15: Added the module parameter.
ast.unparse(ast_obj)
Unparse an
object and generate a string with code that would produce an equivalent ast.AST object if parsed back with
.
Warning
The produced code string will not necessarily be equal to the original code that generated the
object (without any compiler optimizations, such as constant tuples/frozensets).
Warning
Trying to unparse a highly complex expression would result with
.
Added in version 3.9.
ast.literal_eval(node_or_string)
Evaluate an expression node or a string containing only a Python literal or container display. The string or node provided may only consist of the following Python literal structures: strings, bytes, numbers, tuples, lists, dicts, sets, booleans, None and Ellipsis.
This can be used for evaluating strings containing Python values without the need to parse the values oneself. It is not capable of evaluating arbitrarily complex expressions, for example involving operators or indexing.
This function had been documented as “safe” in the past without defining what that meant. That was misleading. This is specifically designed not to execute Python code, unlike the more general
. There is no namespace, no name lookups, or ability to call out. But it is not free from attack: A relatively small input can lead to memory exhaustion or to C stack exhaustion, crashing the process. There is also the possibility for excessive CPU consumption denial of service on some inputs. Calling it on untrusted data is thus not recommended.
Changed in version 3.2: Now allows bytes and set literals.
Changed in version 3.9: Now supports creating empty sets with 'set()'.
Changed in version 3.10: For string inputs, leading spaces and tabs are now stripped.
ast.get_docstring(node, clean=True)
Return the docstring of the given node (which must be a
,
,
, or
node), or None if it has no docstring. If clean is true, clean up the docstring’s indentation with
.
Changed in version 3.5:
is now supported.
ast.get_source_segment(source, node, *, padded=False)
Get source code segment of the source that generated node. If some location information (
,
,
, or
) is missing, return None.
If padded is True, the first line of a multi-line statement will be padded with spaces to match its original position.
Added in version 3.8.
ast.fix_missing_locations(node)
When you compile a node tree with
, the compiler expects
and
attributes for every node that supports them. This is rather tedious to fill in for generated nodes, so this helper adds these attributes recursively where not already set, by setting them to the values of the parent node. It works recursively starting at node.
ast.increment_lineno(node, n=1)
Increment the line number and end line number of each node in the tree starting at node by n. This is useful to “move code” to a different location in a file.
ast.copy_location(new_node, old_node)
Copy source location (
,
,
, and
) from old_node to new_node if possible, and return new_node.
ast.iter_fields(node)
Yield a tuple of (fieldname,value) for each field in node._fields that is present on node.
ast.iter_child_nodes(node)
Yield all direct child nodes of node, that is, all fields that are nodes and all items of fields that are lists of nodes.
ast.walk(node)
Recursively yield all descendant nodes in the tree starting at node (including node itself), in no specified order. This is useful if you only want to modify nodes in place and don’t care about the context.
classast.NodeVisitor
A node visitor base class that walks the abstract syntax tree and calls a visitor function for every node found. This function may return a value which is forwarded by the
method.
This class is meant to be subclassed, with the subclass adding visitor methods.
visit(node)
Visit a node. The default implementation calls the method called self.visit_classname where classname is the name of the node class, or
if that method doesn’t exist.
generic_visit(node)
This visitor calls
on all children of the node.
Note that child nodes of nodes that have a custom visitor method won’t be visited unless the visitor calls generic_visit() or visits them itself.
visit_Constant(node)
Handles all constant nodes.
Don’t use the NodeVisitor if you want to apply changes to nodes during traversal. For this a special visitor exists (
) that allows modifications.
Deprecated since version 3.8, removed in version 3.14: Methods visit_Num(), visit_Str(), visit_Bytes(), visit_NameConstant() and visit_Ellipsis() will not be called in Python 3.14+. Add the
method instead to handle all constant nodes.
classast.NodeTransformer
A
subclass that walks the abstract syntax tree and allows modification of nodes.
The NodeTransformer will walk the AST and use the return value of the visitor methods to replace or remove the old node. If the return value of the visitor method is None, the node will be removed from its location, otherwise it is replaced with the return value. The return value may be the original node in which case no replacement takes place.
Here is an example transformer that rewrites all occurrences of name lookups (foo) to data['foo']:
classRewriteName(NodeTransformer):defvisit_Name(self,node):returnSubscript(value=Name(id='data'),slice=Constant(value=node.id),ctx=node.ctx)Keep in mind that if the node you’re operating on has child nodes you must either transform the child nodes yourself or call the
method for the node first.
For nodes that were part of a collection of statements (that applies to all statement nodes), the visitor may also return a list of nodes rather than just a single node.
If NodeTransformer introduces new nodes (that weren’t part of original tree) without giving them location information (such as
),
should be called with the new sub-tree to recalculate the location information:
tree=ast.parse('foo',mode='eval')new_tree=fix_missing_locations(RewriteName().visit(tree))Usually you use the transformer like this:
node=YourTransformer().visit(node)ast.dump(node, annotate_fields=True, include_attributes=False, *, color=False, indent=None, show_empty=False)
Return a formatted dump of the tree in node. This is mainly useful for debugging purposes. If annotate_fields is true (by default), the returned string will show the names and the values for fields. If annotate_fields is false, the result string will be more compact by omitting unambiguous field names. Attributes such as line numbers and column offsets are not dumped by default. If this is wanted, include_attributes can be set to true.
If color is True, the returned string is syntax highlighted using ANSI escape sequences. If False (the default), colored output is always disabled.
If indent is a non-negative integer or string, then the tree will be pretty-printed with that indent level. An indent level of 0, negative, or "" will only insert newlines. None (the default) selects the single line representation. Using a positive integer indent indents that many spaces per level. If indent is a string (such as "\t"), that string is used to indent each level.
If show_empty is false (the default), optional empty lists and Load() values will be omitted from the output. Optional None values are always omitted.
>>> tree=ast.parse('print(None)','?','eval')>>> print(ast.dump(tree,indent=4))Expression( body=Call( func=Name(id='print'), args=[ Constant(value=None)]))>>> print(ast.dump(tree,indent=4,show_empty=True))Expression( body=Call( func=Name(id='print', ctx=Load()), args=[ Constant(value=None)], keywords=[]))Changed in version 3.9: Added the indent option.
Changed in version 3.13: Added the show_empty option.
Changed in version 3.15: Omit optional Load() values by default.
Changed in version 3.15: Added the color parameter.
ast.compare(a, b, /, *, compare_attributes=False)
Recursively compares two ASTs.
compare_attributes affects whether AST attributes are considered in the comparison. If compare_attributes is False (default), then attributes are ignored. Otherwise they must all be equal. This option is useful to check whether the ASTs are structurally equal but differ in whitespace or similar details. Attributes include line numbers and column offsets.
Added in version 3.14.
Compiler flags
The following flags may be passed to
in order to change effects on the compilation of a program:
ast.PyCF_ALLOW_TOP_LEVEL_AWAIT
Enables support for top-level await, asyncfor, asyncwith and async comprehensions.
Added in version 3.8.
ast.PyCF_ONLY_AST
Generates and returns an abstract syntax tree instead of returning a compiled code object.
ast.PyCF_OPTIMIZED_AST
The returned AST is optimized according to the optimize argument in
or
.
Added in version 3.13.
Enables support for
and
style type comments (#type:<type>, #type:ignore<stuff>).
Added in version 3.8.
Command-line usage
Added in version 3.9.
The ast module can be executed as a script from the command line. It is as simple as:
python-mast[-m<mode>][-a][infile]The following options are accepted:
-h,--help
Show the help message and exit.
-m<mode>
--mode<mode>
Specify what kind of code must be compiled, like the mode argument in
.
Don’t parse type comments.
-a,--include-attributes
Include attributes such as line numbers and column offsets.
-i<indent>
--indent<indent>
Indentation of nodes in AST (number of spaces).
--feature-version<version>
Python version in the format 3.x (for example, 3.10). Defaults to the current version of the interpreter.
Added in version 3.14.
-O<level>
--optimize<level>
Optimization level for parser. Defaults to no optimization.
Added in version 3.14.
--show-empty
Show empty lists and fields that are None. Defaults to not showing empty objects.
Added in version 3.14.
If infile is specified its contents are parsed to AST and dumped to stdout. Otherwise, the content is read from stdin.
See also
, an external documentation resource, has good details on working with Python ASTs.
annotates Python ASTs with the positions of tokens and text in the source code that generated them. This is helpful for tools that make source code transformations.
unifies the token-based and parse-tree-based views of python programs by inserting two-way links between tokens and ast nodes.
parses code as a Concrete Syntax Tree that looks like an ast tree and keeps all formatting details. It’s useful for building automated refactoring (codemod) applications and linters.
is a Python parser that supports error recovery and round-trip parsing for different Python versions (in multiple Python versions). Parso is also able to list multiple syntax errors in your Python file.