Add the "ast" module, containing helpers to ease use of the "_ast" classes.

2 files changed, 400 insertions, 9 deletions

diff --git a/Lib/ast.py b/Lib/ast.py
new file mode 100644
index 0000000..cc4a4b8
--- /dev/null
+++ b/Lib/ast.py
@@ -0,0 +1,300 @@
+# -*- coding: utf-8 -*-
+"""
+    ast
+    ~~~
+
+    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(expr, filename='<unknown>', mode='exec'):
+    """
+    Parse an expression into an AST node.
+    Equivalent to compile(expr, filename, mode, PyCF_ONLY_AST).
+    """
+    return compile(expr, filename, mode, PyCF_ONLY_AST)
+
+
+def literal_eval(node_or_string):
+    """
+    Safely evaluate an expression node or a string containing a Python
+    expression.  The string or node provided may only consist of the following
+    Python literal structures: strings, numbers, tuples, lists, dicts, booleans,
+    and None.
+    """
+    _safe_names = {'None': None, 'True': True, 'False': False}
+    if isinstance(node_or_string, basestring):
+        node_or_string = parse(node_or_string, mode='eval')
+    if isinstance(node_or_string, Expression):
+        node_or_string = node_or_string.body
+    def _convert(node):
+        if isinstance(node, Str):
+            return node.s
+        elif isinstance(node, Num):
+            return node.n
+        elif isinstance(node, Tuple):
+            return tuple(map(_convert, node.elts))
+        elif isinstance(node, List):
+            return list(map(_convert, node.elts))
+        elif isinstance(node, Dict):
+            return dict((_convert(k), _convert(v)) for k, v
+                        in zip(node.keys, node.values))
+        elif isinstance(node, Name):
+            if node.id in _safe_names:
+                return _safe_names[node.id]
+        raise ValueError('malformed string')
+    return _convert(node_or_string)
+
+
+def dump(node, annotate_fields=True, include_attributes=False):
+    """
+    Return a formatted dump of the tree in *node*.  This is mainly useful for
+    debugging purposes.  The returned string will show the names and the values
+    for fields.  This makes the code impossible to evaluate, so if evaluation is
+    wanted *annotate_fields* must be set to False.  Attributes such as line
+    numbers and column offsets are dumped by default.  If this is wanted,
+    *include_attributes* can be set to True.
+    """
+    def _format(node):
+        if isinstance(node, AST):
+            fields = [(a, _format(b)) for a, b in iter_fields(node)]
+            rv = '%s(%s' % (node.__class__.__name__, ', '.join(
+                ('%s=%s' % field for field in fields)
+                if annotate_fields else
+                (b for a, b in fields)
+            ))
+            if include_attributes and node._attributes:
+                rv += fields and ', ' or ' '
+                rv += ', '.join('%s=%s' % (a, _format(getattr(node, a)))
+                                for a in node._attributes)
+            return rv + ')'
+        elif isinstance(node, list):
+            return '[%s]' % ', '.join(_format(x) for x in node)
+        return repr(node)
+    if not isinstance(node, AST):
+        raise TypeError('expected AST, got %r' % node.__class__.__name__)
+    return _format(node)
+
+
+def copy_location(new_node, old_node):
+    """
+    Copy source location (`lineno` and `col_offset` attributes) from
+    *old_node* to *new_node* if possible, and return *new_node*.
+    """
+    for attr in 'lineno', 'col_offset':
+        if attr in old_node._attributes and attr in new_node._attributes \
+           and hasattr(old_node, attr):
+            setattr(new_node, attr, getattr(old_node, attr))
+    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):
+        if 'lineno' in node._attributes:
+            if not hasattr(node, 'lineno'):
+                node.lineno = lineno
+            else:
+                lineno = node.lineno
+        if 'col_offset' in node._attributes:
+            if not hasattr(node, 'col_offset'):
+                node.col_offset = col_offset
+            else:
+                col_offset = node.col_offset
+        for child in iter_child_nodes(node):
+            _fix(child, lineno, col_offset)
+    _fix(node, 1, 0)
+    return node
+
+
+def increment_lineno(node, n=1):
+    """
+    Increment the 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.
+    """
+    if 'lineno' in node._attributes:
+        node.lineno = getattr(node, 'lineno', 0) + n
+    for child in walk(node):
+        if 'lineno' in child._attributes:
+            child.lineno = getattr(child, 'lineno', 0) + 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 not isinstance(node, (FunctionDef, ClassDef, Module)):
+        raise TypeError("%r can't have docstrings" % node.__class__.__name__)
+    if node.body and isinstance(node.body[0], Expr) and \
+       isinstance(node.body[0].value, Str):
+        if clean:
+            import inspect
+            return inspect.cleandoc(node.body[0].value.s)
+        return node.body[0].value.s
+
+
+def walk(node):
+    """
+    Recursively yield all child nodes of *node*, 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
+
+
+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 copy_location(Subscript(
+                   value=Name(id='data', ctx=Load()),
+                   slice=Index(value=Str(s=node.id)),
+                   ctx=node.ctx
+               ), node)
+
+    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):
+            old_value = getattr(node, field, None)
+            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
diff --git a/Lib/test/test_ast.py b/Lib/test/test_ast.py
index 9d2bd66..00a5aae 100644
--- a/Lib/test/test_ast.py
+++ b/Lib/test/test_ast.py
@@ -1,6 +1,6 @@
 import sys, itertools, unittest
 from test import test_support
-import _ast
+import ast
 
 def to_tuple(t):
     if t is None or isinstance(t, (basestring, int, long, complex)):
@@ -123,9 +123,9 @@ eval_tests = [
 class AST_Tests(unittest.TestCase):
 
     def _assert_order(self, ast_node, parent_pos):
-        if not isinstance(ast_node, _ast.AST) or ast_node._fields is None:
+        if not isinstance(ast_node, ast.AST) or ast_node._fields is None:
             return
-        if isinstance(ast_node, (_ast.expr, _ast.stmt, _ast.excepthandler)):
+        if isinstance(ast_node, (ast.expr, ast.stmt, ast.excepthandler)):
             node_pos = (ast_node.lineno, ast_node.col_offset)
             self.assert_(node_pos >= parent_pos)
             parent_pos = (ast_node.lineno, ast_node.col_offset)
@@ -142,29 +142,29 @@ class AST_Tests(unittest.TestCase):
                                     (single_tests, single_results, "single"),
                                     (eval_tests, eval_results, "eval")):
             for i, o in itertools.izip(input, output):
-                ast_tree = compile(i, "?", kind, _ast.PyCF_ONLY_AST)
+                ast_tree = compile(i, "?", kind, ast.PyCF_ONLY_AST)
                 self.assertEquals(to_tuple(ast_tree), o)
                 self._assert_order(ast_tree, (0, 0))
 
     def test_nodeclasses(self):
-        x = _ast.BinOp(1, 2, 3, lineno=0)
+        x = ast.BinOp(1, 2, 3, lineno=0)
         self.assertEquals(x.left, 1)
         self.assertEquals(x.op, 2)
         self.assertEquals(x.right, 3)
         self.assertEquals(x.lineno, 0)
 
         # node raises exception when not given enough arguments
-        self.assertRaises(TypeError, _ast.BinOp, 1, 2)
+        self.assertRaises(TypeError, ast.BinOp, 1, 2)
 
         # can set attributes through kwargs too
-        x = _ast.BinOp(left=1, op=2, right=3, lineno=0)
+        x = ast.BinOp(left=1, op=2, right=3, lineno=0)
         self.assertEquals(x.left, 1)
         self.assertEquals(x.op, 2)
         self.assertEquals(x.right, 3)
         self.assertEquals(x.lineno, 0)
 
         # this used to fail because Sub._fields was None
-        x = _ast.Sub()
+        x = ast.Sub()
 
     def test_pickling(self):
         import pickle
@@ -181,8 +181,99 @@ class AST_Tests(unittest.TestCase):
                     ast2 = mod.loads(mod.dumps(ast, protocol))
                     self.assertEquals(to_tuple(ast2), to_tuple(ast))
 
+
+class ASTHelpers_Test(unittest.TestCase):
+
+    def test_parse(self):
+        a = ast.parse('foo(1 + 1)')
+        b = compile('foo(1 + 1)', '<unknown>', 'exec', ast.PyCF_ONLY_AST)
+        self.assertEqual(ast.dump(a), ast.dump(b))
+
+    def test_dump(self):
+        node = ast.parse('spam(eggs, "and cheese")')
+        self.assertEqual(ast.dump(node),
+            "Module(body=[Expr(value=Call(func=Name(id='spam', ctx=Load()), "
+            "args=[Name(id='eggs', ctx=Load()), Str(s='and cheese')], "
+            "keywords=[], starargs=None, kwargs=None))])"
+        )
+        self.assertEqual(ast.dump(node, annotate_fields=False),
+            "Module([Expr(Call(Name('spam', Load()), [Name('eggs', Load()), "
+            "Str('and cheese')], [], None, None))])"
+        )
+        self.assertEqual(ast.dump(node, include_attributes=True),
+            "Module(body=[Expr(value=Call(func=Name(id='spam', ctx=Load(), "
+            "lineno=1, col_offset=0), args=[Name(id='eggs', ctx=Load(), "
+            "lineno=1, col_offset=5), Str(s='and cheese', lineno=1, "
+            "col_offset=11)], keywords=[], starargs=None, kwargs=None, "
+            "lineno=1, col_offset=0), lineno=1, col_offset=0)])"
+        )
+
+    def test_copy_location(self):
+        src = ast.parse('1 + 1', mode='eval')
+        src.body.right = ast.copy_location(ast.Num(2), src.body.right)
+        self.assertEqual(ast.dump(src, include_attributes=True),
+            'Expression(body=BinOp(left=Num(n=1, lineno=1, col_offset=0), '
+            'op=Add(), right=Num(n=2, lineno=1, col_offset=4), lineno=1, '
+            'col_offset=0))'
+        )
+
+    def test_fix_missing_locations(self):
+        src = ast.parse('write("spam")')
+        src.body.append(ast.Expr(ast.Call(ast.Name('spam', ast.Load()),
+                                          [ast.Str('eggs')], [], None, None)))
+        self.assertEqual(src, ast.fix_missing_locations(src))
+        self.assertEqual(ast.dump(src, include_attributes=True),
+            "Module(body=[Expr(value=Call(func=Name(id='write', ctx=Load(), "
+            "lineno=1, col_offset=0), args=[Str(s='spam', lineno=1, "
+            "col_offset=6)], keywords=[], starargs=None, kwargs=None, "
+            "lineno=1, col_offset=0), lineno=1, col_offset=0), "
+            "Expr(value=Call(func=Name(id='spam', ctx=Load(), lineno=1, "
+            "col_offset=0), args=[Str(s='eggs', lineno=1, col_offset=0)], "
+            "keywords=[], starargs=None, kwargs=None, lineno=1, "
+            "col_offset=0), lineno=1, col_offset=0)])"
+        )
+
+    def test_increment_lineno(self):
+        src = ast.parse('1 + 1', mode='eval')
+        self.assertEqual(ast.increment_lineno(src, n=3), src)
+        self.assertEqual(ast.dump(src, include_attributes=True),
+            'Expression(body=BinOp(left=Num(n=1, lineno=4, col_offset=0), '
+            'op=Add(), right=Num(n=1, lineno=4, col_offset=4), lineno=4, '
+            'col_offset=0))'
+        )
+
+    def test_iter_fields(self):
+        node = ast.parse('foo()', mode='eval')
+        d = dict(ast.iter_fields(node.body))
+        self.assertEqual(d.pop('func').id, 'foo')
+        self.assertEqual(d, {'keywords': [], 'kwargs': None,
+                             'args': [], 'starargs': None})
+
+    def test_iter_child_nodes(self):
+        node = ast.parse("spam(23, 42, eggs='leek')", mode='eval')
+        self.assertEqual(len(list(ast.iter_child_nodes(node.body))), 4)
+        iterator = ast.iter_child_nodes(node.body)
+        self.assertEqual(next(iterator).id, 'spam')
+        self.assertEqual(next(iterator).n, 23)
+        self.assertEqual(next(iterator).n, 42)
+        self.assertEqual(ast.dump(next(iterator)),
+            "keyword(arg='eggs', value=Str(s='leek'))"
+        )
+
+    def test_get_docstring(self):
+        node = ast.parse('def foo():\n  """line one\n  line two"""')
+        self.assertEqual(ast.get_docstring(node.body[0]),
+                         'line one\nline two')
+
+    def test_literal_eval(self):
+        self.assertEqual(ast.literal_eval('[1, 2, 3]'), [1, 2, 3])
+        self.assertEqual(ast.literal_eval('{"foo": 42}'), {"foo": 42})
+        self.assertEqual(ast.literal_eval('(True, False, None)'), (True, False, None))
+        self.assertRaises(ValueError, ast.literal_eval, 'foo()')
+
+
 def test_main():
-    test_support.run_unittest(AST_Tests)
+    test_support.run_unittest(AST_Tests, ASTHelpers_Test)
 
 def main():
     if __name__ != '__main__':