>>>
The default Python prompt of the interactive shell. Often seen for code examples which can be executed interactively in the interpreter.
...
Can refer to:
The default Python prompt of the interactive shell when entering the code for an indented code block, when within a pair of matching left and right delimiters (parentheses, square brackets, curly braces or triple quotes), or after specifying a decorator.
The
built-in constant.
2to3
A tool that tries to convert Python 2.x code to Python 3.x code by handling most of the incompatibilities which can be detected by parsing the source and traversing the parse tree.
2to3 is available in the standard library as
; a standalone entry point is provided as Tools/scripts/2to3. See
2to3 — Automated Python 2 to 3 code translation
.
abstract base class
Abstract base classes complement
by providing a way to define interfaces when other techniques like
would be clumsy or subtly wrong (for example with
). ABCs introduce virtual subclasses, which are classes that don’t inherit from a class but are still recognized by
and
; see the
module documentation. Python comes with many built-in ABCs for data structures (in the
module), numbers (in the
module), streams (in the
module), import finders and loaders (in the
module). You can create your own ABCs with the
module.
annotation
A label associated with a variable, a class attribute or a function parameter or return value, used by convention as a
.
Annotations of local variables cannot be accessed at runtime, but annotations of global variables, class attributes, and functions are stored in the __annotations__ special attribute of modules, classes, and functions, respectively.
See
,
,
and
, which describe this functionality. Also see
for best practices on working with annotations.
argument
A value passed to a
(or
) when calling the function. There are two kinds of argument:
keyword argument: an argument preceded by an identifier (e.g. name=) in a function call or passed as a value in a dictionary preceded by **. For example, 3 and 5 are both keyword arguments in the following calls to
:
complex(real=3,imag=5)complex(**{'real':3,'imag':5})
positional argument: an argument that is not a keyword argument. Positional arguments can appear at the beginning of an argument list and/or be passed as elements of an
preceded by *. For example, 3 and 5 are both positional arguments in the following calls:
complex(3,5)complex(*(3,5))
Arguments are assigned to the named local variables in a function body. See the
section for the rules governing this assignment. Syntactically, any expression can be used to represent an argument; the evaluated value is assigned to the local variable.
See also the
glossary entry, the FAQ question on
the difference between arguments and parameters
, and
.
asynchronous context manager
An object which controls the environment seen in an
statement by defining
and
methods. Introduced by
.
asynchronous generator
A function which returns an
asynchronous generator iterator
. It looks like a coroutine function defined with
except that it contains
expressions for producing a series of values usable in an
loop.
Usually refers to an asynchronous generator function, but may refer to an asynchronous generator iterator in some contexts. In cases where the intended meaning isn’t clear, using the full terms avoids ambiguity.
An asynchronous generator function may contain
expressions as well as
, and
statements.
asynchronous generator iterator
An object created by a
function.
This is an
which when called using the
method returns an awaitable object which will execute the body of the asynchronous generator function until the next
expression.
Each
temporarily suspends processing, remembering the location execution state (including local variables and pending try-statements). When the asynchronous generator iterator effectively resumes with another awaitable returned by
, it picks up where it left off. See
and
.
asynchronous iterable
An object, that can be used in an
statement. Must return an
from its
method. Introduced by
.
asynchronous iterator
An object that implements the
and
methods.
must return an
object.
resolves the awaitables returned by an asynchronous iterator’s
method until it raises a
exception. Introduced by
.
attribute
A value associated with an object which is usually referenced by name using dotted expressions. For example, if an object o has an attribute a it would be referenced as o.a.
It is possible to give an object an attribute whose name is not an identifier as defined by
, for example using
, if the object allows it. Such an attribute will not be accessible using a dotted expression, and would instead need to be retrieved with
.
awaitable
An object that can be used in an
expression. Can be a
or an object with an
method. See also
.
BDFL
Benevolent Dictator For Life, a.k.a.
, Python’s creator.
binary file
A
able to read and write
. Examples of binary files are files opened in binary mode ('rb', 'wb' or 'rb+'),
,
, and instances of
and
.
See also
for a file object able to read and write
objects.
borrowed reference
In Python’s C API, a borrowed reference is a reference to an object, where the code using the object does not own the reference. It becomes a dangling pointer if the object is destroyed. For example, a garbage collection can remove the last
to the object and so destroy it.
Calling
on the
is recommended to convert it to a
in-place, except when the object cannot be destroyed before the last usage of the borrowed reference. The
function can be used to create a new
.
bytes-like object
An object that supports the
and can export a C-
buffer. This includes all
,
, and
objects, as well as many common
objects. Bytes-like objects can be used for various operations that work with binary data; these include compression, saving to a binary file, and sending over a socket.
Some operations need the binary data to be mutable. The documentation often refers to these as “read-write bytes-like objects”. Example mutable buffer objects include
and a
of a
. Other operations require the binary data to be stored in immutable objects (“read-only bytes-like objects”); examples of these include
and a
of a
object.
bytecode
Python source code is compiled into bytecode, the internal representation of a Python program in the CPython interpreter. The bytecode is also cached in .pyc files so that executing the same file is faster the second time (recompilation from source to bytecode can be avoided). This “intermediate language” is said to run on a
that executes the machine code corresponding to each bytecode. Do note that bytecodes are not expected to work between different Python virtual machines, nor to be stable between Python releases.
A list of bytecode instructions can be found in the documentation for
.
callable
A callable is an object that can be called, possibly with a set of arguments (see
), with the following syntax:
callable(argument1,argument2,argumentN)A
, and by extension a
, is a callable. An instance of a class that implements the
method is also a callable.
callback
A subroutine function which is passed as an argument to be executed at some point in the future.
class
A template for creating user-defined objects. Class definitions normally contain method definitions which operate on instances of the class.
class variable
A variable defined in a class and intended to be modified only at class level (i.e., not in an instance of the class).
complex number
An extension of the familiar real number system in which all numbers are expressed as a sum of a real part and an imaginary part. Imaginary numbers are real multiples of the imaginary unit (the square root of -1), often written i in mathematics or j in engineering. Python has built-in support for complex numbers, which are written with this latter notation; the imaginary part is written with a j suffix, e.g., 3+1j. To get access to complex equivalents of the
module, use
. Use of complex numbers is a fairly advanced mathematical feature. If you’re not aware of a need for them, it’s almost certain you can safely ignore them.
context manager
An object which controls the environment seen in a
statement by defining
and
methods. See
.
context variable
A variable which can have different values depending on its context. This is similar to Thread-Local Storage in which each execution thread may have a different value for a variable. However, with context variables, there may be several contexts in one execution thread and the main usage for context variables is to keep track of variables in concurrent asynchronous tasks. See
.
contiguous
A buffer is considered contiguous exactly if it is either C-contiguous or Fortran contiguous. Zero-dimensional buffers are C and Fortran contiguous. In one-dimensional arrays, the items must be laid out in memory next to each other, in order of increasing indexes starting from zero. In multidimensional C-contiguous arrays, the last index varies the fastest when visiting items in order of memory address. However, in Fortran contiguous arrays, the first index varies the fastest.
coroutine
Coroutines are a more generalized form of subroutines. Subroutines are entered at one point and exited at another point. Coroutines can be entered, exited, and resumed at many different points. They can be implemented with the
statement. See also
.
coroutine function
A function which returns a
object. A coroutine function may be defined with the
statement, and may contain
,
, and
keywords. These were introduced by
.
CPython
The canonical implementation of the Python programming language, as distributed on
. The term “CPython” is used when necessary to distinguish this implementation from others such as Jython or IronPython.
decorator
A function returning another function, usually applied as a function transformation using the @wrapper syntax. Common examples for decorators are
and
.
The decorator syntax is merely syntactic sugar, the following two function definitions are semantically equivalent:
deff(arg):...f=staticmethod(f)@staticmethoddeff(arg):...The same concept exists for classes, but is less commonly used there. See the documentation for
and
for more about decorators.
descriptor
Any object which defines the methods
,
, or
. When a class attribute is a descriptor, its special binding behavior is triggered upon attribute lookup. Normally, using a.b to get, set or delete an attribute looks up the object named b in the class dictionary for a, but if b is a descriptor, the respective descriptor method gets called. Understanding descriptors is a key to a deep understanding of Python because they are the basis for many features including functions, methods, properties, class methods, static methods, and reference to super classes.
For more information about descriptors’ methods, see
or the
.
dictionary
An associative array, where arbitrary keys are mapped to values. The keys can be any object with
and
methods. Called a hash in Perl.
dictionary comprehension
A compact way to process all or part of the elements in an iterable and return a dictionary with the results. results={n:n**2forninrange(10)} generates a dictionary containing key n mapped to value n**2. See
Displays for lists, sets and dictionaries
.
dictionary view
The objects returned from
,
, and
are called dictionary views. They provide a dynamic view on the dictionary’s entries, which means that when the dictionary changes, the view reflects these changes. To force the dictionary view to become a full list use list(dictview). See
.
docstring
A string literal which appears as the first expression in a class, function or module. While ignored when the suite is executed, it is recognized by the compiler and put into the __doc__ attribute of the enclosing class, function or module. Since it is available via introspection, it is the canonical place for documentation of the object.
duck-typing
A programming style which does not look at an object’s type to determine if it has the right interface; instead, the method or attribute is simply called or used (“If it looks like a duck and quacks like a duck, it must be a duck.”) By emphasizing interfaces rather than specific types, well-designed code improves its flexibility by allowing polymorphic substitution. Duck-typing avoids tests using
or
. (Note, however, that duck-typing can be complemented with
.) Instead, it typically employs
tests or
programming.
EAFP
Easier to ask for forgiveness than permission. This common Python coding style assumes the existence of valid keys or attributes and catches exceptions if the assumption proves false. This clean and fast style is characterized by the presence of many
and
statements. The technique contrasts with the
style common to many other languages such as C.
expression
A piece of syntax which can be evaluated to some value. In other words, an expression is an accumulation of expression elements like literals, names, attribute access, operators or function calls which all return a value. In contrast to many other languages, not all language constructs are expressions. There are also
s which cannot be used as expressions, such as
. Assignments are also statements, not expressions.
extension module
A module written in C or C++, using Python’s C API to interact with the core and with user code.
f-string
String literals prefixed with 'f' or 'F' are commonly called “f-strings” which is short for
. See also
.
file object
An object exposing a file-oriented API (with methods such as read() or write()) to an underlying resource. Depending on the way it was created, a file object can mediate access to a real on-disk file or to another type of storage or communication device (for example standard input/output, in-memory buffers, sockets, pipes, etc.). File objects are also called file-like objects or streams.
There are actually three categories of file objects: raw
, buffered
and
. Their interfaces are defined in the
module. The canonical way to create a file object is by using the
function.
file-like object
A synonym for
.
filesystem encoding and error handler
Encoding and error handler used by Python to decode bytes from the operating system and encode Unicode to the operating system.
The filesystem encoding must guarantee to successfully decode all bytes below 128. If the file system encoding fails to provide this guarantee, API functions can raise
.
The
and
sys.getfilesystemencodeerrors()
functions can be used to get the filesystem encoding and error handler.
The
filesystem encoding and error handler
are configured at Python startup by the
function: see
and
members of
.
See also the
.
finder
An object that tries to find the
for a module that is being imported.
Since Python 3.3, there are two types of finder:
for use with
, and
for use with
.
See
,
and
for much more detail.
floor division
Mathematical division that rounds down to nearest integer. The floor division operator is //. For example, the expression 11//4 evaluates to 2 in contrast to the 2.75 returned by float true division. Note that (-11)//4 is -3 because that is -2.75 rounded downward. See
.
function
A series of statements which returns some value to a caller. It can also be passed zero or more
which may be used in the execution of the body. See also
,
, and the
section.
function annotation
An
of a function parameter or return value.
Function annotations are usually used for
: for example, this function is expected to take two
arguments and is also expected to have an
return value:
defsum_two_numbers(a:int,b:int)->int:returna+bFunction annotation syntax is explained in section
.
See
and
, which describe this functionality. Also see
for best practices on working with annotations.
__future__
A
, from__future__import<feature>, directs the compiler to compile the current module using syntax or semantics that will become standard in a future release of Python. The
module documents the possible values of feature. By importing this module and evaluating its variables, you can see when a new feature was first added to the language and when it will (or did) become the default:
>>> import__future__>>> __future__.division_Feature((2, 2, 0, 'alpha', 2), (3, 0, 0, 'alpha', 0), 8192)garbage collection
The process of freeing memory when it is not used anymore. Python performs garbage collection via reference counting and a cyclic garbage collector that is able to detect and break reference cycles. The garbage collector can be controlled using the
module.
generator
A function which returns a
. It looks like a normal function except that it contains
expressions for producing a series of values usable in a for-loop or that can be retrieved one at a time with the
function.
Usually refers to a generator function, but may refer to a generator iterator in some contexts. In cases where the intended meaning isn’t clear, using the full terms avoids ambiguity.
generator iterator
An object created by a
function.
Each
temporarily suspends processing, remembering the location execution state (including local variables and pending try-statements). When the generator iterator resumes, it picks up where it left off (in contrast to functions which start fresh on every invocation).
generator expression
An expression that returns an iterator. It looks like a normal expression followed by a for clause defining a loop variable, range, and an optional if clause. The combined expression generates values for an enclosing function:
>>> sum(i*iforiinrange(10))# sum of squares 0, 1, 4, ... 81285generic function
A function composed of multiple functions implementing the same operation for different types. Which implementation should be used during a call is determined by the dispatch algorithm.
See also the
glossary entry, the
decorator, and
.
generic type
A
that can be parameterized; typically a
such as
or
. Used for
and
.
For more details, see
,
,
,
, and the
module.
GIL
See
.
global interpreter lock
The mechanism used by the
interpreter to assure that only one thread executes Python
at a time. This simplifies the CPython implementation by making the object model (including critical built-in types such as
) implicitly safe against concurrent access. Locking the entire interpreter makes it easier for the interpreter to be multi-threaded, at the expense of much of the parallelism afforded by multi-processor machines.
However, some extension modules, either standard or third-party, are designed so as to release the GIL when doing computationally intensive tasks such as compression or hashing. Also, the GIL is always released when doing I/O.
Past efforts to create a “free-threaded” interpreter (one which locks shared data at a much finer granularity) have not been successful because performance suffered in the common single-processor case. It is believed that overcoming this performance issue would make the implementation much more complicated and therefore costlier to maintain.
hash-based pyc
A bytecode cache file that uses the hash rather than the last-modified time of the corresponding source file to determine its validity. See
.
hashable
An object is hashable if it has a hash value which never changes during its lifetime (it needs a
method), and can be compared to other objects (it needs an
method). Hashable objects which compare equal must have the same hash value.
Hashability makes an object usable as a dictionary key and a set member, because these data structures use the hash value internally.
Most of Python’s immutable built-in objects are hashable; mutable containers (such as lists or dictionaries) are not; immutable containers (such as tuples and frozensets) are only hashable if their elements are hashable. Objects which are instances of user-defined classes are hashable by default. They all compare unequal (except with themselves), and their hash value is derived from their
.
IDLE
An Integrated Development and Learning Environment for Python.
is a basic editor and interpreter environment which ships with the standard distribution of Python.
immutable
An object with a fixed value. Immutable objects include numbers, strings and tuples. Such an object cannot be altered. A new object has to be created if a different value has to be stored. They play an important role in places where a constant hash value is needed, for example as a key in a dictionary.
import path
A list of locations (or
) that are searched by the
for modules to import. During import, this list of locations usually comes from
, but for subpackages it may also come from the parent package’s __path__ attribute.
importing
The process by which Python code in one module is made available to Python code in another module.
importer
An object that both finds and loads a module; both a
and
object.
interactive
Python has an interactive interpreter which means you can enter statements and expressions at the interpreter prompt, immediately execute them and see their results. Just launch python with no arguments (possibly by selecting it from your computer’s main menu). It is a very powerful way to test out new ideas or inspect modules and packages (remember help(x)).
interpreted
Python is an interpreted language, as opposed to a compiled one, though the distinction can be blurry because of the presence of the bytecode compiler. This means that source files can be run directly without explicitly creating an executable which is then run. Interpreted languages typically have a shorter development/debug cycle than compiled ones, though their programs generally also run more slowly. See also
.
interpreter shutdown
When asked to shut down, the Python interpreter enters a special phase where it gradually releases all allocated resources, such as modules and various critical internal structures. It also makes several calls to the
. This can trigger the execution of code in user-defined destructors or weakref callbacks. Code executed during the shutdown phase can encounter various exceptions as the resources it relies on may not function anymore (common examples are library modules or the warnings machinery).
The main reason for interpreter shutdown is that the __main__ module or the script being run has finished executing.
iterable
An object capable of returning its members one at a time. Examples of iterables include all sequence types (such as
,
, and
) and some non-sequence types like
,
, and objects of any classes you define with an
method or with a
method that implements
semantics.
Iterables can be used in a
loop and in many other places where a sequence is needed (
,
, …). When an iterable object is passed as an argument to the built-in function
, it returns an iterator for the object. This iterator is good for one pass over the set of values. When using iterables, it is usually not necessary to call
or deal with iterator objects yourself. The
statement does that automatically for you, creating a temporary unnamed variable to hold the iterator for the duration of the loop. See also
,
, and
.
iterator
An object representing a stream of data. Repeated calls to the iterator’s
method (or passing it to the built-in function
) return successive items in the stream. When no more data are available a
exception is raised instead. At this point, the iterator object is exhausted and any further calls to its __next__() method just raise
again. Iterators are required to have an
method that returns the iterator object itself so every iterator is also iterable and may be used in most places where other iterables are accepted. One notable exception is code which attempts multiple iteration passes. A container object (such as a
) produces a fresh new iterator each time you pass it to the
function or use it in a
loop. Attempting this with an iterator will just return the same exhausted iterator object used in the previous iteration pass, making it appear like an empty container.
More information can be found in
.
CPython implementation detail: CPython does not consistently apply the requirement that an iterator define
.
key function
A key function or collation function is a callable that returns a value used for sorting or ordering. For example,
is used to produce a sort key that is aware of locale specific sort conventions.
A number of tools in Python accept key functions to control how elements are ordered or grouped. They include
,
,
,
,
,
,
, and
.
There are several ways to create a key function. For example. the
method can serve as a key function for case insensitive sorts. Alternatively, a key function can be built from a
expression such as lambdar:(r[0],r[2]). Also,
,
, and
are three key function constructors. See the
for examples of how to create and use key functions.
keyword argument
See
.
lambda
An anonymous inline function consisting of a single
which is evaluated when the function is called. The syntax to create a lambda function is lambda[parameters]:expression
LBYL
Look before you leap. This coding style explicitly tests for pre-conditions before making calls or lookups. This style contrasts with the
approach and is characterized by the presence of many
statements.
In a multi-threaded environment, the LBYL approach can risk introducing a race condition between “the looking” and “the leaping”. For example, the code, ifkeyinmapping:returnmapping[key] can fail if another thread removes key from mapping after the test, but before the lookup. This issue can be solved with locks or by using the EAFP approach.
list
A built-in Python
. Despite its name it is more akin to an array in other languages than to a linked list since access to elements is O(1).
list comprehension
A compact way to process all or part of the elements in a sequence and return a list with the results. result=['{:#04x}'.format(x)forxinrange(256)ifx%2==0] generates a list of strings containing even hex numbers (0x..) in the range from 0 to 255. The
clause is optional. If omitted, all elements in range(256) are processed.
loader
An object that loads a module. It must define a method named load_module(). A loader is typically returned by a
. See
for details and
for an
.
locale encoding
On Unix, it is the encoding of the LC_CTYPE locale. It can be set with
locale.setlocale(locale.LC_CTYPE, new_locale)
.
On Windows, it is the ANSI code page (ex: "cp1252").
On Android and VxWorks, Python uses "utf-8" as the locale encoding.
can be used to get the locale encoding.
See also the
filesystem encoding and error handler
.
magic method
An informal synonym for
.
mapping
A container object that supports arbitrary key lookups and implements the methods specified in the
or
collections.abc.MutableMapping
. Examples include
,
,
and
.
meta path finder
A
returned by a search of
. Meta path finders are related to, but different from
.
See
for the methods that meta path finders implement.
metaclass
The class of a class. Class definitions create a class name, a class dictionary, and a list of base classes. The metaclass is responsible for taking those three arguments and creating the class. Most object oriented programming languages provide a default implementation. What makes Python special is that it is possible to create custom metaclasses. Most users never need this tool, but when the need arises, metaclasses can provide powerful, elegant solutions. They have been used for logging attribute access, adding thread-safety, tracking object creation, implementing singletons, and many other tasks.
More information can be found in
.
method
A function which is defined inside a class body. If called as an attribute of an instance of that class, the method will get the instance object as its first
(which is usually called self). See
and
.
method resolution order
Method Resolution Order is the order in which base classes are searched for a member during lookup. See
The Python 2.3 Method Resolution Order
for details of the algorithm used by the Python interpreter since the 2.3 release.
module
An object that serves as an organizational unit of Python code. Modules have a namespace containing arbitrary Python objects. Modules are loaded into Python by the process of
.
See also
.
module spec
A namespace containing the import-related information used to load a module. An instance of
importlib.machinery.ModuleSpec
.
MRO
See
.
mutable
Mutable objects can change their value but keep their
. See also
.
named tuple
The term “named tuple” applies to any type or class that inherits from tuple and whose indexable elements are also accessible using named attributes. The type or class may have other features as well.
Several built-in types are named tuples, including the values returned by
and
. Another example is
:
>>> sys.float_info[1]# indexed access1024>>> sys.float_info.max_exp# named field access1024>>> isinstance(sys.float_info,tuple)# kind of tupleTrueSome named tuples are built-in types (such as the above examples). Alternatively, a named tuple can be created from a regular class definition that inherits from
and that defines named fields. Such a class can be written by hand, or it can be created by inheriting
, or with the factory function
. The latter techniques also add some extra methods that may not be found in hand-written or built-in named tuples.
namespace
The place where a variable is stored. Namespaces are implemented as dictionaries. There are the local, global and built-in namespaces as well as nested namespaces in objects (in methods). Namespaces support modularity by preventing naming conflicts. For instance, the functions
and
are distinguished by their namespaces. Namespaces also aid readability and maintainability by making it clear which module implements a function. For instance, writing
or
makes it clear that those functions are implemented by the
and
modules, respectively.
namespace package
A
which serves only as a container for subpackages. Namespace packages may have no physical representation, and specifically are not like a
because they have no __init__.py file.
See also
.
nested scope
The ability to refer to a variable in an enclosing definition. For instance, a function defined inside another function can refer to variables in the outer function. Note that nested scopes by default work only for reference and not for assignment. Local variables both read and write in the innermost scope. Likewise, global variables read and write to the global namespace. The
allows writing to outer scopes.
new-style class
Old name for the flavor of classes now used for all class objects. In earlier Python versions, only new-style classes could use Python’s newer, versatile features like
, descriptors, properties,
, class methods, and static methods.
object
Any data with state (attributes or value) and defined behavior (methods). Also the ultimate base class of any
.
package
A Python
which can contain submodules or recursively, subpackages. Technically, a package is a Python module with a __path__ attribute.
See also
and
.
parameter
A named entity in a
(or method) definition that specifies an
(or in some cases, arguments) that the function can accept. There are five kinds of parameter:
positional-or-keyword: specifies an argument that can be passed either
or as a
. This is the default kind of parameter, for example foo and bar in the following:
deffunc(foo,bar=None):...
positional-only: specifies an argument that can be supplied only by position. Positional-only parameters can be defined by including a / character in the parameter list of the function definition after them, for example posonly1 and posonly2 in the following:
deffunc(posonly1,posonly2,/,positional_or_keyword):...
keyword-only: specifies an argument that can be supplied only by keyword. Keyword-only parameters can be defined by including a single var-positional parameter or bare * in the parameter list of the function definition before them, for example kw_only1 and kw_only2 in the following:
deffunc(arg,*,kw_only1,kw_only2):...
var-positional: specifies that an arbitrary sequence of positional arguments can be provided (in addition to any positional arguments already accepted by other parameters). Such a parameter can be defined by prepending the parameter name with *, for example args in the following:
deffunc(*args,**kwargs):...
var-keyword: specifies that arbitrarily many keyword arguments can be provided (in addition to any keyword arguments already accepted by other parameters). Such a parameter can be defined by prepending the parameter name with **, for example kwargs in the example above.
Parameters can specify both optional and required arguments, as well as default values for some optional arguments.
See also the
glossary entry, the FAQ question on
the difference between arguments and parameters
, the
class, the
section, and
.
path entry
A single location on the
which the
consults to find modules for importing.
path entry finder
A
returned by a callable on
(i.e. a
) which knows how to locate modules given a
.
See
for the methods that path entry finders implement.
path entry hook
A callable on the
list which returns a
if it knows how to find modules on a specific
.
path based finder
One of the default
which searches an
for modules.
path-like object
An object representing a file system path. A path-like object is either a
or
object representing a path, or an object implementing the
protocol. An object that supports the
protocol can be converted to a
or
file system path by calling the
function;
and
can be used to guarantee a
or
result instead, respectively. Introduced by
.
PEP
Python Enhancement Proposal. A PEP is a design document providing information to the Python community, or describing a new feature for Python or its processes or environment. PEPs should provide a concise technical specification and a rationale for proposed features.
PEPs are intended to be the primary mechanisms for proposing major new features, for collecting community input on an issue, and for documenting the design decisions that have gone into Python. The PEP author is responsible for building consensus within the community and documenting dissenting opinions.
See
.
portion
A set of files in a single directory (possibly stored in a zip file) that contribute to a namespace package, as defined in
.
positional argument
See
.
provisional API
A provisional API is one which has been deliberately excluded from the standard library’s backwards compatibility guarantees. While major changes to such interfaces are not expected, as long as they are marked provisional, backwards incompatible changes (up to and including removal of the interface) may occur if deemed necessary by core developers. Such changes will not be made gratuitously – they will occur only if serious fundamental flaws are uncovered that were missed prior to the inclusion of the API.
Even for provisional APIs, backwards incompatible changes are seen as a “solution of last resort” - every attempt will still be made to find a backwards compatible resolution to any identified problems.
This process allows the standard library to continue to evolve over time, without locking in problematic design errors for extended periods of time. See
for more details.
provisional package
See
.
Python 3000
Nickname for the Python 3.x release line (coined long ago when the release of version 3 was something in the distant future.) This is also abbreviated “Py3k”.
Pythonic
An idea or piece of code which closely follows the most common idioms of the Python language, rather than implementing code using concepts common to other languages. For example, a common idiom in Python is to loop over all elements of an iterable using a
statement. Many other languages don’t have this type of construct, so people unfamiliar with Python sometimes use a numerical counter instead:
foriinrange(len(food)):print(food[i])As opposed to the cleaner, Pythonic method:
forpieceinfood:print(piece)qualified name
A dotted name showing the “path” from a module’s global scope to a class, function or method defined in that module, as defined in
. For top-level functions and classes, the qualified name is the same as the object’s name:
>>> classC:... classD:... defmeth(self):... pass...>>> C.__qualname__'C'>>> C.D.__qualname__'C.D'>>> C.D.meth.__qualname__'C.D.meth'When used to refer to modules, the fully qualified name means the entire dotted path to the module, including any parent packages, e.g. email.mime.text:
>>> importemail.mime.text>>> email.mime.text.__name__'email.mime.text'reference count
The number of references to an object. When the reference count of an object drops to zero, it is deallocated. Reference counting is generally not visible to Python code, but it is a key element of the
implementation. Programmers can call the
function to return the reference count for a particular object.
regular package
A traditional
, such as a directory containing an __init__.py file.
See also
.
__slots__
A declaration inside a class that saves memory by pre-declaring space for instance attributes and eliminating instance dictionaries. Though popular, the technique is somewhat tricky to get right and is best reserved for rare cases where there are large numbers of instances in a memory-critical application.
sequence
An
which supports efficient element access using integer indices via the
special method and defines a
method that returns the length of the sequence. Some built-in sequence types are
,
,
, and
. Note that
also supports
and __len__(), but is considered a mapping rather than a sequence because the lookups use arbitrary
keys rather than integers.
The
abstract base class defines a much richer interface that goes beyond just
and
, adding count(), index(),
, and
. Types that implement this expanded interface can be registered explicitly using
. For more documentation on sequence methods generally, see
.
set comprehension
A compact way to process all or part of the elements in an iterable and return a set with the results. results={cforcin'abracadabra'ifcnotin'abc'} generates the set of strings {'r','d'}. See
Displays for lists, sets and dictionaries
.
single dispatch
A form of
dispatch where the implementation is chosen based on the type of a single argument.
slice
An object usually containing a portion of a
. A slice is created using the subscript notation, [] with colons between numbers when several are given, such as in variable_name[1:3:5]. The bracket (subscript) notation uses
objects internally.
special method
A method that is called implicitly by Python to execute a certain operation on a type, such as addition. Such methods have names starting and ending with double underscores. Special methods are documented in
.
statement
A statement is part of a suite (a “block” of code). A statement is either an
or one of several constructs with a keyword, such as
,
or
.
static type checker
An external tool that reads Python code and analyzes it, looking for issues such as incorrect types. See also
and the
module.
strong reference
In Python’s C API, a strong reference is a reference to an object which is owned by the code holding the reference. The strong reference is taken by calling
when the reference is created and released with
when the reference is deleted.
The
function can be used to create a strong reference to an object. Usually, the
function must be called on the strong reference before exiting the scope of the strong reference, to avoid leaking one reference.
See also
.
text encoding
A string in Python is a sequence of Unicode code points (in range U+0000–U+10FFFF). To store or transfer a string, it needs to be serialized as a sequence of bytes.
Serializing a string into a sequence of bytes is known as “encoding”, and recreating the string from the sequence of bytes is known as “decoding”.
There are a variety of different text serialization
, which are collectively referred to as “text encodings”.
text file
A
able to read and write
objects. Often, a text file actually accesses a byte-oriented datastream and handles the
automatically. Examples of text files are files opened in text mode ('r' or 'w'),
,
, and instances of
.
See also
for a file object able to read and write
.
triple-quoted string
A string which is bound by three instances of either a quotation mark (”) or an apostrophe (‘). While they don’t provide any functionality not available with single-quoted strings, they are useful for a number of reasons. They allow you to include unescaped single and double quotes within a string and they can span multiple lines without the use of the continuation character, making them especially useful when writing docstrings.
type
The type of a Python object determines what kind of object it is; every object has a type. An object’s type is accessible as its
attribute or can be retrieved with type(obj).
type alias
A synonym for a type, created by assigning the type to an identifier.
Type aliases are useful for simplifying
. For example:
defremove_gray_shades(colors:list[tuple[int,int,int]])->list[tuple[int,int,int]]:passcould be made more readable like this:
Color=tuple[int,int,int]defremove_gray_shades(colors:list[Color])->list[Color]:passSee
and
, which describe this functionality.
type hint
An
that specifies the expected type for a variable, a class attribute, or a function parameter or return value.
Type hints are optional and are not enforced by Python but they are useful to
. They can also aid IDEs with code completion and refactoring.
Type hints of global variables, class attributes, and functions, but not local variables, can be accessed using
.
See
and
, which describe this functionality.
universal newlines
A manner of interpreting text streams in which all of the following are recognized as ending a line: the Unix end-of-line convention '\n', the Windows convention '\r\n', and the old Macintosh convention '\r'. See
and
, as well as
for an additional use.
variable annotation
An
of a variable or a class attribute.
When annotating a variable or a class attribute, assignment is optional:
classC:field:'annotation'Variable annotations are usually used for
: for example this variable is expected to take
values:
count:int=0Variable annotation syntax is explained in section
Annotated assignment statements
.
See
,
and
, which describe this functionality. Also see
for best practices on working with annotations.
virtual environment
A cooperatively isolated runtime environment that allows Python users and applications to install and upgrade Python distribution packages without interfering with the behaviour of other Python applications running on the same system.
See also
.
virtual machine
A computer defined entirely in software. Python’s virtual machine executes the
emitted by the bytecode compiler.
Zen of Python
Listing of Python design principles and philosophies that are helpful in understanding and using the language. The listing can be found by typing “importthis” at the interactive prompt.