python/Lib/ast.py at master · pylee/python · GitHub

History

313 lines (269 loc) · 11.6 KB

Raw

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

201

202

203

204

205

206

207

208

209

210

211

212

213

214

215

216

217

218

219

220

221

222

223

224

225

226

227

228

229

230

231

232

233

234

235

236

237

238

239

240

241

242

243

244

245

246

247

248

249

250

251

252

253

254

255

256

257

258

259

260

261

262

263

264

265

266

267

268

269

270

271

272

273

274

275

276

277

278

279

280

281

282

283

284

285

286

287

288

289

290

291

292

293

294

295

296

297

298

299

300

301

302

303

304

305

306

307

308

309

310

311

312

313

# -*- 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).

:license: Python License.

"""

from _ast import *

from _ast import __version__

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]

elif isinstance(node, BinOp) and \

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

isinstance(node.right, Num) and \

isinstance(node.right.n, complex) and \

isinstance(node.left, Num) and \

isinstance(node.left.n, (int, long, float)):

left = node.left.n

right = node.right.n

if isinstance(node.op, Add):

return left + right

else:

return left - right

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 not 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

python/Lib/ast.py at master · pylee/python · GitHub

Expand file tree

Breadcrumbs

ast.py

Latest commit

History

Breadcrumbs

ast.py

File metadata and controls