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:mod:`!ast` --- Abstract syntax trees
=====================================
.. module:: ast
:synopsis: Abstract Syntax Tree classes and manipulation.
.. testsetup::
import ast
**Source code:** :source:`Lib/ast.py`
--------------
The :mod:`!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 :data:`ast.PyCF_ONLY_AST` as
a flag to the :func:`compile` built-in function, or using the :func:`parse`
helper provided in this module. The result will be a tree of objects whose
classes all inherit from :class:`ast.AST`. An abstract syntax tree can be
compiled into a Python code object using the built-in :func:`compile` function.
.. _abstract-grammar:
Abstract grammar
----------------
The abstract grammar is currently defined as follows:
.. literalinclude:: ../../Parser/Python.asdl
:language: asdl
.. _ast_nodes:
Node classes
------------
.. class:: AST
This is the abstract base of all AST node classes. The actual node classes are
derived from the :file:`Parser/Python.asdl` file, which is reproduced
:ref:`above <abstract-grammar>`. They are defined in the :mod:`!_ast` C
module and re-exported in :mod:`!ast`.
There is one class defined for each left-hand side symbol in the abstract
grammar (for example, :class:`!ast.stmt` or :class:`!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,
:class:`ast.BinOp` inherits from :class:`!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.
.. index:: single: ? (question mark); in AST grammar
.. index:: single: * (asterisk); in AST grammar
.. attribute:: _fields
Each concrete class has an attribute :attr:`!_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, :class:`ast.BinOp`
instances have an attribute :attr:`!left` of type :class:`!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 :func:`compile`.
.. attribute:: _field_types
The :attr:`!_field_types` attribute on each concrete class is a dictionary
mapping field names (as also listed in :attr:`_fields`) to their types.
.. doctest::
>>> ast.TypeVar._field_types
{'name': <class 'str'>, 'bound': ast.expr | None, 'default_value': ast.expr | None}
.. versionadded:: 3.13
.. attribute:: lineno
col_offset
end_lineno
end_col_offset
Instances of :class:`ast.expr` and :class:`ast.stmt` subclasses have
:attr:`lineno`, :attr:`col_offset`, :attr:`end_lineno`, and
:attr:`end_col_offset` attributes. The :attr:`lineno` and :attr:`end_lineno`
are the first and last line numbers of source text span (1-indexed so the
first line is line 1) and the :attr:`col_offset` and :attr:`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 constructors of AST node classes parse their arguments as follows:
* If there are positional arguments, there must be as many as there are items
in :attr:`!_fields`; they will be assigned to attributes with
the corresponding 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 :class:`ast.UnaryOp` 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 :class:`!ast.expr_context` is omitted, it defaults to
:class:`Load() <ast.Load>`. If any other field is omitted, a :exc:`DeprecationWarning` is raised
and the AST node will not have this field. In Python 3.15, this condition will
raise an error.
.. versionchanged:: 3.8
Class :class:`ast.Constant` is now used for all constants.
.. versionchanged:: 3.9
Simple indices are represented by their value, extended slices are
represented as tuples.
.. versionchanged:: 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 :class:`!ast.expr_context` default to
:class:`Load() <ast.Load>`. Previously, omitted attributes would not exist on constructed
nodes (accessing them raised :exc:`AttributeError`).
.. versionchanged:: 3.14
The :meth:`~object.__repr__` output of :class:`~ast.AST` nodes includes
the values of the node fields.
.. deprecated-removed:: 3.8 3.14
Previous versions of Python provided the AST classes :class:`!ast.Num`,
:class:`!ast.Str`, :class:`!ast.Bytes`, :class:`!ast.NameConstant` and
:class:`!ast.Ellipsis`, which were deprecated in Python 3.8. These classes
were removed in Python 3.14, and their functionality has been replaced with
:class:`ast.Constant`.
.. deprecated:: 3.9
Old classes :class:`!ast.Index` and :class:`!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-removed:: 3.13 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 :exc:`TypeError`.
.. deprecated-removed:: 3.15 3.20
In the :ref:`grammar above <abstract-grammar>`, 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 `Green Tree
Snakes <https://greentreesnakes.readthedocs.io/en/latest/>`__ project and
all its contributors.
.. _ast-root-nodes:
Root nodes
^^^^^^^^^^
.. class:: Module(body, type_ignores)
A Python module, as with :ref:`file input <file-input>`.
Node type generated by :func:`ast.parse` in the default ``"exec"`` *mode*.
``body`` is a :class:`list` of the module's :ref:`ast-statements`.
``type_ignores`` is a :class:`list` of the module's type ignore comments;
see :func:`ast.parse` for more details.
.. doctest::
>>> print(ast.dump(ast.parse('x = 1'), indent=4))
Module(
body=[
Assign(
targets=[
Name(id='x', ctx=Store())],
value=Constant(value=1))])
.. class:: Expression(body)
A single Python :ref:`expression input <expression-input>`.
Node type generated by :func:`ast.parse` when *mode* is ``"eval"``.
``body`` is a single node,
one of the :ref:`expression types <ast-expressions>`.
.. doctest::
>>> print(ast.dump(ast.parse('123', mode='eval'), indent=4))
Expression(
body=Constant(value=123))
.. class:: Interactive(body)
A single :ref:`interactive input <interactive>`, like in :ref:`tut-interac`.
Node type generated by :func:`ast.parse` when *mode* is ``"single"``.
``body`` is a :class:`list` of :ref:`statement nodes <ast-statements>`.
.. doctest::
>>> 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))])
.. class:: FunctionType(argtypes, returns)
A representation of an old-style type comments for functions,
as Python versions prior to 3.5 didn't support :pep:`484` annotations.
Node type generated by :func:`ast.parse` when *mode* is ``"func_type"``.
Such type comments would look like this::
def sum_two_number(a, b):
# type: (int, int) -> int
return a + b
``argtypes`` is a :class:`list` of :ref:`expression nodes <ast-expressions>`.
``returns`` is a single :ref:`expression node <ast-expressions>`.
.. doctest::
>>> 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')))
.. versionadded:: 3.8
Literals
^^^^^^^^
.. class:: 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 :class:`str`,
:class:`bytes`, :class:`int`, :class:`float`, :class:`complex`, and :class:`bool`,
and the constants :data:`None` and :data:`Ellipsis`.
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``.
.. doctest::
>>> 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'))
.. class:: 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 :class:`JoinedStr`.
* ``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`` :func:`ASCII <ascii>` formatting
* 114 (``ord('r')``): ``!r`` :func:`repr` formatting
* 115 (``ord('s')``): ``!s`` :func:`string <str>` formatting
* ``format_spec`` is a :class:`JoinedStr` 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.
.. class:: JoinedStr(values)
An f-string, comprising a series of :class:`FormattedValue` and :class:`Constant`
nodes.
.. doctest::
>>> 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')]))]))
.. class:: TemplateStr(values, /)
.. versionadded:: 3.14
Node representing a template string literal, comprising a series of
:class:`Interpolation` and :class:`Constant` nodes.
These nodes may be any order, and do not need to be interleaved.
.. doctest::
>>> 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')]))]))
.. class:: Interpolation(value, str, conversion, format_spec=None)
.. versionadded:: 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 :func:`ast.unparse`. 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`` :func:`ASCII <ascii>` conversion
* 114 (``ord('r')``): ``!r`` :func:`repr` conversion
* 115 (``ord('s')``): ``!s`` :func:`string <str>` conversion
This has the same meaning as ``FormattedValue.conversion``.
* ``format_spec`` is a :class:`JoinedStr` 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``.
.. class:: List(elts, ctx)
Tuple(elts, ctx)
A list or tuple. ``elts`` holds a list of nodes representing the elements.
``ctx`` is :class:`Store` if the container is an assignment target (i.e.
``(x,y)=something``), and :class:`Load` otherwise.
.. doctest::
>>> 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)]))
.. class:: Set(elts)
A set. ``elts`` holds a list of nodes representing the set's elements.
.. doctest::
>>> 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)]))
.. class:: 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 :code:`dictionary.keys()` and :code:`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``.
.. doctest::
>>> 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
^^^^^^^^^
.. class:: Name(id, ctx)
A variable name. ``id`` holds the name as a string, and ``ctx`` is one of
the following types.
.. class:: Load()
Store()
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.
.. doctest::
>>> 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())])])
.. class:: Starred(value, ctx)
A ``*var`` variable reference. ``value`` holds the variable, typically a
:class:`Name` node. This type must be used when building a :class:`Call`
node with ``*args``.
.. doctest::
>>> 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'))])
.. _ast-expressions:
Expressions
^^^^^^^^^^^
.. class:: 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 :class:`Constant`, a
:class:`Name`, a :class:`Lambda`, a :class:`Yield` or :class:`YieldFrom` node.
.. doctest::
>>> print(ast.dump(ast.parse('-a'), indent=4))
Module(
body=[
Expr(
value=UnaryOp(
op=USub(),
operand=Name(id='a')))])
.. class:: UnaryOp(op, operand)
A unary operation. ``op`` is the operator, and ``operand`` any expression
node.
.. class:: UAdd
USub
Not
Invert
Unary operator tokens. :class:`Not` is the ``not`` keyword, :class:`Invert`
is the ``~`` operator.
.. doctest::
>>> print(ast.dump(ast.parse('not x', mode='eval'), indent=4))
Expression(
body=UnaryOp(
op=Not(),
operand=Name(id='x')))
.. class:: BinOp(left, op, right)
A binary operation (like addition or division). ``op`` is the operator, and
``left`` and ``right`` are any expression nodes.
.. doctest::
>>> print(ast.dump(ast.parse('x + y', mode='eval'), indent=4))
Expression(
body=BinOp(
left=Name(id='x'),
op=Add(),
right=Name(id='y')))
.. class:: Add
Sub
Mult
Div
FloorDiv
Mod
Pow
LShift
RShift
BitOr
BitXor
BitAnd
MatMult
Binary operator tokens.
.. class:: BoolOp(op, values)
A boolean operation, 'or' or 'and'. ``op`` is :class:`Or` or :class:`And`.
``values`` are the values involved. Consecutive operations with the same
operator, such as ``a or b or c``, are collapsed into one node with several
values.
This doesn't include ``not``, which is a :class:`UnaryOp`.
.. doctest::
>>> print(ast.dump(ast.parse('x or y', mode='eval'), indent=4))
Expression(
body=BoolOp(
op=Or(),
values=[
Name(id='x'),
Name(id='y')]))
.. class:: And
Or
Boolean operator tokens.
.. class:: 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.
.. doctest::
>>> 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)]))
.. class:: Eq
NotEq
Lt
LtE
Gt
GtE
Is
IsNot
In
NotIn
Comparison operator tokens.
.. class:: Call(func, args, keywords)
A function call. ``func`` is the function, which will often be a
:class:`Name` or :class:`Attribute` object. Of the arguments:
* ``args`` holds a list of the arguments passed by position.
* ``keywords`` holds a list of :class:`.keyword` objects representing
arguments passed by keyword.
The ``args`` and ``keywords`` arguments are optional and default to empty lists.
.. doctest::
>>> 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'))]))
.. class:: 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.
.. class:: IfExp(test, body, orelse)
An expression such as ``a if b else c``. Each field holds a single node, so
in the following example, all three are :class:`Name` nodes.
.. doctest::
>>> 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')))
.. class:: Attribute(value, attr, ctx)
Attribute access, e.g. ``d.keys``. ``value`` is a node, typically a
:class:`Name`. ``attr`` is a bare string giving the name of the attribute,
and ``ctx`` is :class:`Load`, :class:`Store` or :class:`Del` according to how
the attribute is acted on.
.. doctest::
>>> print(ast.dump(ast.parse('snake.colour', mode='eval'), indent=4))
Expression(
body=Attribute(
value=Name(id='snake'),
attr='colour'))
.. class:: 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 :class:`Assign`
node in which the first argument can be multiple nodes, in this case both
``target`` and ``value`` must be single nodes.
.. doctest::
>>> print(ast.dump(ast.parse('(x := 4)', mode='eval'), indent=4))
Expression(
body=NamedExpr(
target=Name(id='x', ctx=Store()),
value=Constant(value=4)))
.. versionadded:: 3.8
Subscripting
~~~~~~~~~~~~
.. class:: 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 :class:`Tuple` and contain a :class:`Slice`.
``ctx`` is :class:`Load`, :class:`Store` or :class:`Del`
according to the action performed with the subscript.
.. doctest::
>>> 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)])))
.. class:: Slice(lower, upper, step)
Regular slicing (on the form ``lower:upper`` or ``lower:upper:step``).
Can occur only inside the *slice* field of :class:`Subscript`, either
directly or as an element of :class:`Tuple`.
.. doctest::
>>> 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
~~~~~~~~~~~~~~
.. class:: ListComp(elt, generators)
SetComp(elt, generators)
GeneratorExp(elt, generators)
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
``{**item for item in items}``, the expression to be expanded goes in
``key`` and ``value`` is ``None``.
``generators`` is a list of :class:`comprehension` nodes.
.. doctest::
>>> 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)]))
.. class:: comprehension(target, iter, ifs, is_async)
One ``for`` clause in a comprehension. ``target`` is the reference to use for
each element - typically a :class:`Name` or :class:`Tuple` 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
``async for`` instead of ``for``). The value is an integer (0 or 1).
.. doctest::
>>> 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 comprehension
Expression(
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 comprehension
Expression(
body=ListComp(
elt=Name(id='i'),
generators=[
comprehension(
target=Name(id='i', ctx=Store()),
iter=Name(id='soc'),
is_async=1)]))
.. _ast-statements:
Statements
^^^^^^^^^^
.. class:: 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 :class:`Tuple` or :class:`List`
within ``targets``.
.. attribute:: type_comment
``type_comment`` is an optional string with the type annotation as a comment.
.. doctest::
>>> print(ast.dump(ast.parse('a = b = 1'), indent=4)) # Multiple assignment
Module(
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)) # Unpacking
Module(
body=[
Assign(
targets=[
Tuple(
elts=[
Name(id='a', ctx=Store()),
Name(id='b', ctx=Store())],
ctx=Store())],
value=Name(id='c'))])
.. class:: AnnAssign(target, annotation, value, simple)
An assignment with a type annotation. ``target`` is a single node and can
be a :class:`Name`, an :class:`Attribute` or a :class:`Subscript`.
``annotation`` is the annotation, such as a :class:`Constant` or :class:`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
:class:`Name` node that does not appear between parentheses; all other
targets are considered complex. Only simple targets appear in
the :attr:`~object.__annotations__` dictionary of modules and classes.
.. doctest::
>>> 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 parenthesis
Module(
body=[
AnnAssign(
target=Name(id='a', ctx=Store()),
annotation=Name(id='int'),
value=Constant(value=1),