cpython/Lib/ast.py

"""
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).

:copyright: Copyright 2008 by Armin Ronacher.
:license: Python License.
"""
from _ast import *


def parse(source, filename='<unknown>', mode='exec', *,
          type_comments=False, feature_version=None, optimize=-1):
    """
    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)


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')
    if isinstance(node_or_string, Expression):
        node_or_string = node_or_string.body
    def _raise_malformed_node(node):
        msg = "malformed node or string"
        if lno := getattr(node, 'lineno', None):
            msg += f' on line {lno}'
        raise ValueError(msg + f': {node!r}')
    def _convert_num(node):
        if not isinstance(node, Constant) or type(node.value) not in (int, float, complex):
            _raise_malformed_node(node)
        return node.value
    def _convert_signed_num(node):
        if isinstance(node, UnaryOp) and isinstance(node.op, (UAdd, USub)):
            operand = _convert_num(node.operand)
            if isinstance(node.op, UAdd):
                return + operand
            else:
                return - operand
        return _convert_num(node)
    def _convert(node):
        if isinstance(node, Constant):
            return node.value
        elif isinstance(node, Tuple):
            return tuple(map(_convert, node.elts))
        elif isinstance(node, List):
            return list(map(_convert, node.elts))
        elif isinstance(node, Set):
            return set(map(_convert, node.elts))
        elif (isinstance(node, Call) and isinstance(node.func, Name) and
              node.func.id == 'set' and node.args == node.keywords == []):
            return set()
        elif isinstance(node, Dict):
            if len(node.keys) != len(node.values):
                _raise_malformed_node(node)
            return dict(zip(map(_convert, node.keys),
                            map(_convert, node.values)))
        elif isinstance(node, BinOp) and isinstance(node.op, (Add, Sub)):
            left = _convert_signed_num(node.left)
            right = _convert_num(node.right)
            if isinstance(left, (int, float)) and isinstance(right, complex):
                if isinstance(node.op, Add):
                    return left + right
                else:
                    return left - right
        return _convert_signed_num(node)
    return _convert(node_or_string)


def dump(
    node, annotate_fields=True, include_attributes=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 indent is a non-negative
    integer or string, then the tree will be pretty-printed with that indent
    level. None (the default) selects the single line representation.
    If show_empty is False, then empty lists and fields that are None
    will be omitted from the output for better readability.
    """
    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(repr(value))
                            continue
                    if not keywords:
                        args.extend(args_buffer)
                        args_buffer = []
                value, simple = _format(value, level)
                allsimple = allsimple and simple
                if keywords:
                    args.append('%s=%s' % (name, 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('%s=%s' % (name, value))
            if allsimple and len(args) <= 3:
                return '%s(%s)' % (node.__class__.__name__, ', '.join(args)), not args
            return '%s(%s%s)' % (node.__class__.__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
        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(
    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
    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(
                a,
                b,
                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(color=True)
    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 (default -1)')
    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)
    print(dump(tree, include_attributes=args.include_attributes,
               indent=args.indent, show_empty=args.show_empty))

if __name__ == '__main__':
    main()