1 # -*- coding: utf-8 -*- 2 """ 3 ast 4 ~~~ 5 6 The `ast` module helps Python applications to process trees of the Python 7 abstract syntax grammar. The abstract syntax itself might change with 8 each Python release; this module helps to find out programmatically what 9 the current grammar looks like and allows modifications of it. 10 11 An abstract syntax tree can be generated by passing `ast.PyCF_ONLY_AST` as 12 a flag to the `compile()` builtin function or by using the `parse()` 13 function from this module. The result will be a tree of objects whose 14 classes all inherit from `ast.AST`. 15 16 A modified abstract syntax tree can be compiled into a Python code object 17 using the built-in `compile()` function. 18 19 Additionally various helper functions are provided that make working with 20 the trees simpler. The main intention of the helper functions and this 21 module in general is to provide an easy to use interface for libraries 22 that work tightly with the python syntax (template engines for example). 23 24 25 :copyright: Copyright 2008 by Armin Ronacher. 26 :license: Python License. 27 """ 28 from _ast import * 29 from _ast import __version__ 30 31 32 def parse(source, filename='<unknown>', mode='exec'): 33 """ 34 Parse the source into an AST node. 35 Equivalent to compile(source, filename, mode, PyCF_ONLY_AST). 36 """ 37 return compile(source, filename, mode, PyCF_ONLY_AST) 38 39 40 def literal_eval(node_or_string): 41 """ 42 Safely evaluate an expression node or a string containing a Python 43 expression. The string or node provided may only consist of the following 44 Python literal structures: strings, numbers, tuples, lists, dicts, booleans, 45 and None. 46 """ 47 _safe_names = {'None': None, 'True': True, 'False': False} 48 if isinstance(node_or_string, basestring): 49 node_or_string = parse(node_or_string, mode='eval') 50 if isinstance(node_or_string, Expression): 51 node_or_string = node_or_string.body 52 def _convert(node): 53 if isinstance(node, Str): 54 return node.s 55 elif isinstance(node, Num): 56 return node.n 57 elif isinstance(node, Tuple): 58 return tuple(map(_convert, node.elts)) 59 elif isinstance(node, List): 60 return list(map(_convert, node.elts)) 61 elif isinstance(node, Dict): 62 return dict((_convert(k), _convert(v)) for k, v 63 in zip(node.keys, node.values)) 64 elif isinstance(node, Name): 65 if node.id in _safe_names: 66 return _safe_names[node.id] 67 elif isinstance(node, BinOp) and \ 68 isinstance(node.op, (Add, Sub)) and \ 69 isinstance(node.right, Num) and \ 70 isinstance(node.right.n, complex) and \ 71 isinstance(node.left, Num) and \ 72 isinstance(node.left.n, (int, long, float)): 73 left = node.left.n 74 right = node.right.n 75 if isinstance(node.op, Add): 76 return left + right 77 else: 78 return left - right 79 raise ValueError('malformed string') 80 return _convert(node_or_string) 81 82 83 def dump(node, annotate_fields=True, include_attributes=False): 84 """ 85 Return a formatted dump of the tree in *node*. This is mainly useful for 86 debugging purposes. The returned string will show the names and the values 87 for fields. This makes the code impossible to evaluate, so if evaluation is 88 wanted *annotate_fields* must be set to False. Attributes such as line 89 numbers and column offsets are not dumped by default. If this is wanted, 90 *include_attributes* can be set to True. 91 """ 92 def _format(node): 93 if isinstance(node, AST): 94 fields = [(a, _format(b)) for a, b in iter_fields(node)] 95 rv = '%s(%s' % (node.__class__.__name__, ', '.join( 96 ('%s=%s' % field for field in fields) 97 if annotate_fields else 98 (b for a, b in fields) 99 )) 100 if include_attributes and node._attributes: 101 rv += fields and ', ' or ' ' 102 rv += ', '.join('%s=%s' % (a, _format(getattr(node, a))) 103 for a in node._attributes) 104 return rv + ')' 105 elif isinstance(node, list): 106 return '[%s]' % ', '.join(_format(x) for x in node) 107 return repr(node) 108 if not isinstance(node, AST): 109 raise TypeError('expected AST, got %r' % node.__class__.__name__) 110 return _format(node) 111 112 113 def copy_location(new_node, old_node): 114 """ 115 Copy source location (`lineno` and `col_offset` attributes) from 116 *old_node* to *new_node* if possible, and return *new_node*. 117 """ 118 for attr in 'lineno', 'col_offset': 119 if attr in old_node._attributes and attr in new_node._attributes \ 120 and hasattr(old_node, attr): 121 setattr(new_node, attr, getattr(old_node, attr)) 122 return new_node 123 124 125 def fix_missing_locations(node): 126 """ 127 When you compile a node tree with compile(), the compiler expects lineno and 128 col_offset attributes for every node that supports them. This is rather 129 tedious to fill in for generated nodes, so this helper adds these attributes 130 recursively where not already set, by setting them to the values of the 131 parent node. It works recursively starting at *node*. 132 """ 133 def _fix(node, lineno, col_offset): 134 if 'lineno' in node._attributes: 135 if not hasattr(node, 'lineno'): 136 node.lineno = lineno 137 else: 138 lineno = node.lineno 139 if 'col_offset' in node._attributes: 140 if not hasattr(node, 'col_offset'): 141 node.col_offset = col_offset 142 else: 143 col_offset = node.col_offset 144 for child in iter_child_nodes(node): 145 _fix(child, lineno, col_offset) 146 _fix(node, 1, 0) 147 return node 148 149 150 def increment_lineno(node, n=1): 151 """ 152 Increment the line number of each node in the tree starting at *node* by *n*. 153 This is useful to "move code" to a different location in a file. 154 """ 155 for child in walk(node): 156 if 'lineno' in child._attributes: 157 child.lineno = getattr(child, 'lineno', 0) + n 158 return node 159 160 161 def iter_fields(node): 162 """ 163 Yield a tuple of ``(fieldname, value)`` for each field in ``node._fields`` 164 that is present on *node*. 165 """ 166 for field in node._fields: 167 try: 168 yield field, getattr(node, field) 169 except AttributeError: 170 pass 171 172 173 def iter_child_nodes(node): 174 """ 175 Yield all direct child nodes of *node*, that is, all fields that are nodes 176 and all items of fields that are lists of nodes. 177 """ 178 for name, field in iter_fields(node): 179 if isinstance(field, AST): 180 yield field 181 elif isinstance(field, list): 182 for item in field: 183 if isinstance(item, AST): 184 yield item 185 186 187 def get_docstring(node, clean=True): 188 """ 189 Return the docstring for the given node or None if no docstring can 190 be found. If the node provided does not have docstrings a TypeError 191 will be raised. 192 """ 193 if not isinstance(node, (FunctionDef, ClassDef, Module)): 194 raise TypeError("%r can't have docstrings" % node.__class__.__name__) 195 if node.body and isinstance(node.body[0], Expr) and \ 196 isinstance(node.body[0].value, Str): 197 if clean: 198 import inspect 199 return inspect.cleandoc(node.body[0].value.s) 200 return node.body[0].value.s 201 202 203 def walk(node): 204 """ 205 Recursively yield all descendant nodes in the tree starting at *node* 206 (including *node* itself), in no specified order. This is useful if you 207 only want to modify nodes in place and don't care about the context. 208 """ 209 from collections import deque 210 todo = deque([node]) 211 while todo: 212 node = todo.popleft() 213 todo.extend(iter_child_nodes(node)) 214 yield node 215 216 217 class NodeVisitor(object): 218 """ 219 A node visitor base class that walks the abstract syntax tree and calls a 220 visitor function for every node found. This function may return a value 221 which is forwarded by the `visit` method. 222 223 This class is meant to be subclassed, with the subclass adding visitor 224 methods. 225 226 Per default the visitor functions for the nodes are ``'visit_'`` + 227 class name of the node. So a `TryFinally` node visit function would 228 be `visit_TryFinally`. This behavior can be changed by overriding 229 the `visit` method. If no visitor function exists for a node 230 (return value `None`) the `generic_visit` visitor is used instead. 231 232 Don't use the `NodeVisitor` if you want to apply changes to nodes during 233 traversing. For this a special visitor exists (`NodeTransformer`) that 234 allows modifications. 235 """ 236 237 def visit(self, node): 238 """Visit a node.""" 239 method = 'visit_' + node.__class__.__name__ 240 visitor = getattr(self, method, self.generic_visit) 241 return visitor(node) 242 243 def generic_visit(self, node): 244 """Called if no explicit visitor function exists for a node.""" 245 for field, value in iter_fields(node): 246 if isinstance(value, list): 247 for item in value: 248 if isinstance(item, AST): 249 self.visit(item) 250 elif isinstance(value, AST): 251 self.visit(value) 252 253 254 class NodeTransformer(NodeVisitor): 255 """ 256 A :class:`NodeVisitor` subclass that walks the abstract syntax tree and 257 allows modification of nodes. 258 259 The `NodeTransformer` will walk the AST and use the return value of the 260 visitor methods to replace or remove the old node. If the return value of 261 the visitor method is ``None``, the node will be removed from its location, 262 otherwise it is replaced with the return value. The return value may be the 263 original node in which case no replacement takes place. 264 265 Here is an example transformer that rewrites all occurrences of name lookups 266 (``foo``) to ``data['foo']``:: 267 268 class RewriteName(NodeTransformer): 269 270 def visit_Name(self, node): 271 return copy_location(Subscript( 272 value=Name(id='data', ctx=Load()), 273 slice=Index(value=Str(s=node.id)), 274 ctx=node.ctx 275 ), node) 276 277 Keep in mind that if the node you're operating on has child nodes you must 278 either transform the child nodes yourself or call the :meth:`generic_visit` 279 method for the node first. 280 281 For nodes that were part of a collection of statements (that applies to all 282 statement nodes), the visitor may also return a list of nodes rather than 283 just a single node. 284 285 Usually you use the transformer like this:: 286 287 node = YourTransformer().visit(node) 288 """ 289 290 def generic_visit(self, node): 291 for field, old_value in iter_fields(node): 292 old_value = getattr(node, field, None) 293 if isinstance(old_value, list): 294 new_values = [] 295 for value in old_value: 296 if isinstance(value, AST): 297 value = self.visit(value) 298 if value is None: 299 continue 300 elif not isinstance(value, AST): 301 new_values.extend(value) 302 continue 303 new_values.append(value) 304 old_value[:] = new_values 305 elif isinstance(old_value, AST): 306 new_node = self.visit(old_value) 307 if new_node is None: 308 delattr(node, field) 309 else: 310 setattr(node, field, new_node) 311 return node 312
