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"""

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 and allows modifications of it.

An abstract syntax tree can be generated by passing `ast.PyCF_ONLY_AST` as

a flag to the `compile()` builtin function or by using the `parse()`

function from this module. The result will be a tree of objects whose

classes all inherit from `ast.AST`.

A modified abstract syntax tree can be compiled into a Python code object

using the built-in `compile()` function.

Additionally various helper functions are provided that make working with

the trees simpler. The main intention of the helper functions and this

module in general is to provide an easy to use interface for libraries

that work tightly with the python syntax (template engines for example).

:license: Python License.

"""

from _ast import *

def 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, PyCF_ONLY_AST).

Pass type_comments=True to get back type comments where the syntax allows.

"""

flags = PyCF_ONLY_AST

if optimize > 0:

flags |= PyCF_OPTIMIZED_AST

if type_comments:

flags |= PyCF_TYPE_COMMENTS

if feature_version is None:

feature_version = -1

elif isinstance(feature_version, tuple):

major, minor = feature_version # Should be a 2-tuple.

if major != 3:

raise ValueError(f"Unsupported major version: {major}")

feature_version = minor

# Else it should be an int giving the minor version for 3.x.

return compile(source, filename, mode, flags,

_feature_version=feature_version, optimize=optimize,

module=module)

def literal_eval(node_or_string):

"""

Evaluate an expression node or a string containing only a Python

expression. The string or node provided may only consist of the following

Python literal structures: strings, bytes, numbers, tuples, lists, dicts,

sets, booleans, and None.

Caution: A complex expression can overflow the C stack and cause a crash.

"""

if isinstance(node_or_string, str):

node_or_string = parse(node_or_string.lstrip(" \t"), mode='eval').body

elif isinstance(node_or_string, Expression):

node_or_string = node_or_string.body

return _convert_literal(node_or_string)

def _convert_literal(node):

"""

Used by `literal_eval` to convert an AST node into a value.

"""

if isinstance(node, Constant):

return node.value

if isinstance(node, Dict) and len(node.keys) == len(node.values):

return dict(zip(

map(_convert_literal, node.keys),

map(_convert_literal, node.values),

))

if isinstance(node, Tuple):

return tuple(map(_convert_literal, node.elts))

if isinstance(node, List):

return list(map(_convert_literal, node.elts))

if isinstance(node, Set):

return set(map(_convert_literal, node.elts))

if (

isinstance(node, Call) and isinstance(node.func, Name)

and node.func.id == 'set' and node.args == node.keywords == []

return set()

if (

isinstance(node, UnaryOp)

and isinstance(node.op, (UAdd, USub))

and isinstance(node.operand, Constant)

and type(operand := node.operand.value) in (int, float, complex)

if isinstance(node.op, UAdd):

return + operand

else:

return - operand

if (

isinstance(node, BinOp)

and isinstance(node.op, (Add, Sub))

and isinstance(node.left, (Constant, UnaryOp))

and isinstance(node.right, Constant)

and type(left := _convert_literal(node.left)) in (int, float)

and type(right := _convert_literal(node.right)) is complex

if isinstance(node.op, Add):

return left + right

else:

return left - right

msg = "malformed node or string"

if lno := getattr(node, 'lineno', None):

msg += f' on line {lno}'

raise ValueError(msg + f': {node!r}')

def 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 color is 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. If indent is None (the default),

the tree is dumped on a single line.

If show_empty is False, then empty lists and fields that are None

will be omitted from the output for better readability.

"""

from _colorize import get_theme

t = get_theme(force_color=color, force_no_color=not color).ast

def _format(node, level=0):

if indent is not None:

level += 1

prefix = '\n' + indent * level

sep = ',\n' + indent * level

else:

prefix = ''

sep = ', '

if isinstance(node, AST):

cls = type(node)

args = []

args_buffer = []

allsimple = True

keywords = annotate_fields

for name in node._fields:

try:

value = getattr(node, name)

except AttributeError:

keywords = True

continue

if value is None and getattr(cls, name, ...) is None:

keywords = True

continue

if not show_empty:

if value == []:

field_type = cls._field_types.get(name, object)

if getattr(field_type, '__origin__', ...) is list:

if not keywords:

args_buffer.append(repr(value))

continue

elif isinstance(value, Load):

field_type = cls._field_types.get(name, object)

if field_type is expr_context:

if not keywords:

args_buffer.append(

f'{t.node}{type(value).__name__}'

f'{t.reset}()')

continue

if not keywords:

args.extend(args_buffer)

args_buffer = []

value, simple = _format(value, level)

allsimple = allsimple and simple

if keywords:

args.append(f'{t.field}{name}{t.reset}={value}')

else:

args.append(value)

if include_attributes and node._attributes:

for name in node._attributes:

try:

value = getattr(node, name)

except AttributeError:

continue

if value is None and getattr(cls, name, ...) is None:

continue

value, simple = _format(value, level)

allsimple = allsimple and simple

args.append(f'{t.attribute}{name}{t.reset}={value}')

cls_name = f'{t.node}{cls.__name__}{t.reset}'

if allsimple and len(args) <= 3:

return f'{cls_name}({", ".join(args)})', not args

return f'{cls_name}({prefix}{sep.join(args)})', False

elif isinstance(node, list):

if not node:

return '[]', True

return '[%s%s]' % (prefix, sep.join(_format(x, level)[0] for x in node)), False

if isinstance(node, bool) or node is None or node is Ellipsis:

return f'{t.keyword}{node!r}{t.reset}', True

if isinstance(node, (int, float, complex)):

return f'{t.number}{node!r}{t.reset}', True

if isinstance(node, (str, bytes)):

return f'{t.string}{node!r}{t.reset}', True

return repr(node), True

if not isinstance(node, AST):

raise TypeError('expected AST, got %r' % node.__class__.__name__)

if indent is not None and not isinstance(indent, str):

indent = ' ' * indent

return _format(node)[0]

def copy_location(new_node, old_node):

"""

Copy source location (`lineno`, `col_offset`, `end_lineno`, and `end_col_offset`

attributes) from *old_node* to *new_node* if possible, and return *new_node*.

"""

for attr in 'lineno', 'col_offset', 'end_lineno', 'end_col_offset':

if attr in old_node._attributes and attr in new_node._attributes:

value = getattr(old_node, attr, None)

# end_lineno and end_col_offset are optional attributes, and they

# should be copied whether the value is None or not.

if value is not None or (

hasattr(old_node, attr) and attr.startswith("end_")

setattr(new_node, attr, value)

return new_node

def fix_missing_locations(node):

"""

When you compile a node tree with compile(), the compiler expects lineno and

col_offset 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*.

"""

def _fix(node, lineno, col_offset, end_lineno, end_col_offset):

if 'lineno' in node._attributes:

if not hasattr(node, 'lineno'):

node.lineno = lineno

else:

lineno = node.lineno

if 'end_lineno' in node._attributes:

if getattr(node, 'end_lineno', None) is None:

node.end_lineno = end_lineno

else:

end_lineno = node.end_lineno

if 'col_offset' in node._attributes:

if not hasattr(node, 'col_offset'):

node.col_offset = col_offset

else:

col_offset = node.col_offset

if 'end_col_offset' in node._attributes:

if getattr(node, 'end_col_offset', None) is None:

node.end_col_offset = end_col_offset

else:

end_col_offset = node.end_col_offset

for child in iter_child_nodes(node):

_fix(child, lineno, col_offset, end_lineno, end_col_offset)

_fix(node, 1, 0, 1, 0)

return node

def 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.

"""

for child in walk(node):

# TypeIgnore is a special case where lineno is not an attribute

# but rather a field of the node itself.

if isinstance(child, TypeIgnore):

child.lineno = getattr(child, 'lineno', 0) + n

continue

if 'lineno' in child._attributes:

child.lineno = getattr(child, 'lineno', 0) + n

if (

"end_lineno" in child._attributes

and (end_lineno := getattr(child, "end_lineno", 0)) is not None

child.end_lineno = end_lineno + n

return node

def iter_fields(node):

"""

Yield a tuple of ``(fieldname, value)`` for each field in ``node._fields``

that is present on *node*.

"""

for field in node._fields:

try:

yield field, getattr(node, field)

except AttributeError:

pass

def 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.

"""

for name, field in iter_fields(node):

if isinstance(field, AST):

yield field

elif isinstance(field, list):

for item in field:

if isinstance(item, AST):

yield item

def get_docstring(node, clean=True):

"""

Return the docstring for the given node or None if no docstring can

be found. If the node provided does not have docstrings a TypeError

will be raised.

If *clean* is `True`, all tabs are expanded to spaces and any whitespace

that can be uniformly removed from the second line onwards is removed.

"""

if not isinstance(node, (AsyncFunctionDef, FunctionDef, ClassDef, Module)):

raise TypeError("%r can't have docstrings" % node.__class__.__name__)

if not(node.body and isinstance(node.body[0], Expr)):

return None

node = node.body[0].value

if isinstance(node, Constant) and isinstance(node.value, str):

text = node.value

else:

return None

if clean:

import inspect

text = inspect.cleandoc(text)

return text

_line_pattern = None

def _splitlines_no_ff(source, maxlines=None):

"""Split a string into lines ignoring form feed and other chars.

This mimics how the Python parser splits source code.

"""

global _line_pattern

if _line_pattern is None:

# lazily computed to speedup import time of `ast`

import re

_line_pattern = re.compile(r"(.*?(?:\r\n|\n|\r|$))")

lines = []

for lineno, match in enumerate(_line_pattern.finditer(source), 1):

if maxlines is not None and lineno > maxlines:

break

lines.append(match[0])

return lines

def _pad_whitespace(source):

r"""Replace all chars except '\f\t' in a line with spaces."""

result = ''

for c in source:

if c in '\f\t':

result += c

else:

result += ' '

return result

def get_source_segment(source, node, *, padded=False):

"""Get source code segment of the *source* that generated *node*.

If some location information (`lineno`, `end_lineno`, `col_offset`,

or `end_col_offset`) 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.

"""

try:

if node.end_lineno is None or node.end_col_offset is None:

return None

lineno = node.lineno - 1

end_lineno = node.end_lineno - 1

col_offset = node.col_offset

end_col_offset = node.end_col_offset

except AttributeError:

return None

lines = _splitlines_no_ff(source, maxlines=end_lineno+1)

if end_lineno == lineno:

return lines[lineno].encode()[col_offset:end_col_offset].decode()

if padded:

padding = _pad_whitespace(lines[lineno].encode()[:col_offset].decode())

else:

padding = ''

first = padding + lines[lineno].encode()[col_offset:].decode()

last = lines[end_lineno].encode()[:end_col_offset].decode()

lines = lines[lineno+1:end_lineno]

lines.insert(0, first)

lines.append(last)

return ''.join(lines)

def 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.

"""

from collections import deque

todo = deque([node])

while todo:

node = todo.popleft()

todo.extend(iter_child_nodes(node))

yield node

def compare(

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

might differ in whitespace or similar details.

"""

sentinel = object() # handle the possibility of a missing attribute/field

def _compare(a, b):

# Compare two fields on an AST object, which may themselves be

# AST objects, lists of AST objects, or primitive ASDL types

# like identifiers and constants.

if isinstance(a, AST):

return compare(

compare_attributes=compare_attributes,

)

elif isinstance(a, list):

# If a field is repeated, then both objects will represent

# the value as a list.

if len(a) != len(b):

return False

for a_item, b_item in zip(a, b):

if not _compare(a_item, b_item):

return False

else:

return True

else:

return type(a) is type(b) and a == b

def _compare_fields(a, b):

if a._fields != b._fields:

return False

for field in a._fields:

a_field = getattr(a, field, sentinel)

b_field = getattr(b, field, sentinel)

if a_field is sentinel and b_field is sentinel:

# both nodes are missing a field at runtime

continue

if a_field is sentinel or b_field is sentinel:

# one of the node is missing a field

return False

if not _compare(a_field, b_field):

return False

else:

return True

def _compare_attributes(a, b):

if a._attributes != b._attributes:

return False

# Attributes are always ints.

for attr in a._attributes:

a_attr = getattr(a, attr, sentinel)

b_attr = getattr(b, attr, sentinel)

if a_attr is sentinel and b_attr is sentinel:

# both nodes are missing an attribute at runtime

continue

if a_attr != b_attr:

return False

else:

return True

if type(a) is not type(b):

return False

if not _compare_fields(a, b):

return False

if compare_attributes and not _compare_attributes(a, b):

return False

return True

class NodeVisitor(object):

"""

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 `visit` method.

This class is meant to be subclassed, with the subclass adding visitor

methods.

Per default the visitor functions for the nodes are ``'visit_'`` +

class name of the node. So a `TryFinally` node visit function would

be `visit_TryFinally`. This behavior can be changed by overriding

the `visit` method. If no visitor function exists for a node

(return value `None`) the `generic_visit` visitor is used instead.

Don't use the `NodeVisitor` if you want to apply changes to nodes during

traversing. For this a special visitor exists (`NodeTransformer`) that

allows modifications.

"""

def visit(self, node):

"""Visit a node."""

method = 'visit_' + node.__class__.__name__

visitor = getattr(self, method, self.generic_visit)

return visitor(node)

def generic_visit(self, node):

"""Called if no explicit visitor function exists for a node."""

for field, value in iter_fields(node):

if isinstance(value, list):

for item in value:

if isinstance(item, AST):

self.visit(item)

elif isinstance(value, AST):

self.visit(value)

class NodeTransformer(NodeVisitor):

"""

A :class:`NodeVisitor` 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']``::

class RewriteName(NodeTransformer):

def visit_Name(self, node):

return Subscript(

value=Name(id='data', ctx=Load()),

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 :meth:`generic_visit`

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.

Usually you use the transformer like this::

node = YourTransformer().visit(node)

"""

def generic_visit(self, node):

for field, old_value in iter_fields(node):

if isinstance(old_value, list):

new_values = []

for value in old_value:

if isinstance(value, AST):

value = self.visit(value)

if value is None:

continue

elif not isinstance(value, AST):

new_values.extend(value)

continue

new_values.append(value)

old_value[:] = new_values

elif isinstance(old_value, AST):

new_node = self.visit(old_value)

if new_node is None:

delattr(node, field)

else:

setattr(node, field, new_node)

return node

class slice(AST):

"""Deprecated AST node class."""

class Index(slice):

"""Deprecated AST node class. Use the index value directly instead."""

def __new__(cls, value, **kwargs):

return value

class ExtSlice(slice):

"""Deprecated AST node class. Use ast.Tuple instead."""

def __new__(cls, dims=(), **kwargs):

return Tuple(list(dims), Load(), **kwargs)

# If the ast module is loaded more than once, only add deprecated methods once

if not hasattr(Tuple, 'dims'):

# The following code is for backward compatibility.

# It will be removed in future.

def _dims_getter(self):

"""Deprecated. Use elts instead."""

return self.elts

def _dims_setter(self, value):

self.elts = value

Tuple.dims = property(_dims_getter, _dims_setter)

class Suite(mod):

"""Deprecated AST node class. Unused in Python 3."""

class AugLoad(expr_context):

"""Deprecated AST node class. Unused in Python 3."""

class AugStore(expr_context):

"""Deprecated AST node class. Unused in Python 3."""

class Param(expr_context):

"""Deprecated AST node class. Unused in Python 3."""

def unparse(ast_obj):

global _Unparser

try:

unparser = _Unparser()

except NameError:

from _ast_unparse import Unparser as _Unparser

unparser = _Unparser()

return unparser.visit(ast_obj)

def main(args=None):

import argparse

import sys

parser = argparse.ArgumentParser(formatter_class=argparse.ArgumentDefaultsHelpFormatter)

parser.add_argument('infile', nargs='?', default='-',

help='the file to parse; defaults to `stdin`')

parser.add_argument('-m', '--mode', default='exec',

choices=('exec', 'single', 'eval', 'func_type'),

help='specify what kind of code must be parsed')

parser.add_argument('--no-type-comments', default=True, action='store_false',

help="don't add information about type comments")

parser.add_argument('-a', '--include-attributes', action='store_true',

help='include attributes such as line numbers and '

'column offsets')

parser.add_argument('-i', '--indent', type=int, default=3,

help='indentation of nodes (number of spaces)')

parser.add_argument('--feature-version',

type=str, default=None, metavar='VERSION',

help='Python version in the format `3.x` '

'(for example, `3.10`)')

parser.add_argument('-O', '--optimize',

type=int, default=-1, metavar='LEVEL',

help='optimization level for parser')

parser.add_argument('--show-empty', default=False, action='store_true',

help='show empty lists and fields in dump output')

args = parser.parse_args(args)

if args.infile == '-':

name = '<stdin>'

source = sys.stdin.buffer.read()

else:

name = args.infile

with open(args.infile, 'rb') as infile:

source = infile.read()

# Process feature_version

feature_version = None

if args.feature_version:

try:

major, minor = map(int, args.feature_version.split('.', 1))

except ValueError:

parser.error('Invalid format for --feature-version; '

'expected format 3.x (for example, 3.10)')

feature_version = (major, minor)

tree = parse(source, name, args.mode, type_comments=args.no_type_comments,

feature_version=feature_version, optimize=args.optimize)

from _colorize import can_colorize

print(dump(tree, include_attributes=args.include_attributes,

color=can_colorize(file=sys.stdout),

indent=args.indent, show_empty=args.show_empty))

if __name__ == '__main__':

main()

cpython/Lib/ast.py at 3.15 · python/cpython · GitHub

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