/usr/lib/python3/dist-packages/contextlib2.py is in python3-contextlib2 0.5.5-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 | """contextlib2 - backports and enhancements to the contextlib module"""
import sys
import warnings
from collections import deque
from functools import wraps
__all__ = ["contextmanager", "closing", "ContextDecorator", "ExitStack",
"redirect_stdout", "redirect_stderr", "suppress"]
# Backwards compatibility
__all__ += ["ContextStack"]
class ContextDecorator(object):
"A base class or mixin that enables context managers to work as decorators."
def refresh_cm(self):
"""Returns the context manager used to actually wrap the call to the
decorated function.
The default implementation just returns *self*.
Overriding this method allows otherwise one-shot context managers
like _GeneratorContextManager to support use as decorators via
implicit recreation.
DEPRECATED: refresh_cm was never added to the standard library's
ContextDecorator API
"""
warnings.warn("refresh_cm was never added to the standard library",
DeprecationWarning)
return self._recreate_cm()
def _recreate_cm(self):
"""Return a recreated instance of self.
Allows an otherwise one-shot context manager like
_GeneratorContextManager to support use as
a decorator via implicit recreation.
This is a private interface just for _GeneratorContextManager.
See issue #11647 for details.
"""
return self
def __call__(self, func):
@wraps(func)
def inner(*args, **kwds):
with self._recreate_cm():
return func(*args, **kwds)
return inner
class _GeneratorContextManager(ContextDecorator):
"""Helper for @contextmanager decorator."""
def __init__(self, func, args, kwds):
self.gen = func(*args, **kwds)
self.func, self.args, self.kwds = func, args, kwds
# Issue 19330: ensure context manager instances have good docstrings
doc = getattr(func, "__doc__", None)
if doc is None:
doc = type(self).__doc__
self.__doc__ = doc
# Unfortunately, this still doesn't provide good help output when
# inspecting the created context manager instances, since pydoc
# currently bypasses the instance docstring and shows the docstring
# for the class instead.
# See http://bugs.python.org/issue19404 for more details.
def _recreate_cm(self):
# _GCM instances are one-shot context managers, so the
# CM must be recreated each time a decorated function is
# called
return self.__class__(self.func, self.args, self.kwds)
def __enter__(self):
try:
return next(self.gen)
except StopIteration:
raise RuntimeError("generator didn't yield")
def __exit__(self, type, value, traceback):
if type is None:
try:
next(self.gen)
except StopIteration:
return
else:
raise RuntimeError("generator didn't stop")
else:
if value is None:
# Need to force instantiation so we can reliably
# tell if we get the same exception back
value = type()
try:
self.gen.throw(type, value, traceback)
raise RuntimeError("generator didn't stop after throw()")
except StopIteration as exc:
# Suppress StopIteration *unless* it's the same exception that
# was passed to throw(). This prevents a StopIteration
# raised inside the "with" statement from being suppressed.
return exc is not value
except RuntimeError as exc:
# Don't re-raise the passed in exception
if exc is value:
return False
# Likewise, avoid suppressing if a StopIteration exception
# was passed to throw() and later wrapped into a RuntimeError
# (see PEP 479).
if _HAVE_EXCEPTION_CHAINING and exc.__cause__ is value:
return False
raise
except:
# only re-raise if it's *not* the exception that was
# passed to throw(), because __exit__() must not raise
# an exception unless __exit__() itself failed. But throw()
# has to raise the exception to signal propagation, so this
# fixes the impedance mismatch between the throw() protocol
# and the __exit__() protocol.
#
if sys.exc_info()[1] is not value:
raise
def contextmanager(func):
"""@contextmanager decorator.
Typical usage:
@contextmanager
def some_generator(<arguments>):
<setup>
try:
yield <value>
finally:
<cleanup>
This makes this:
with some_generator(<arguments>) as <variable>:
<body>
equivalent to this:
<setup>
try:
<variable> = <value>
<body>
finally:
<cleanup>
"""
@wraps(func)
def helper(*args, **kwds):
return _GeneratorContextManager(func, args, kwds)
return helper
class closing(object):
"""Context to automatically close something at the end of a block.
Code like this:
with closing(<module>.open(<arguments>)) as f:
<block>
is equivalent to this:
f = <module>.open(<arguments>)
try:
<block>
finally:
f.close()
"""
def __init__(self, thing):
self.thing = thing
def __enter__(self):
return self.thing
def __exit__(self, *exc_info):
self.thing.close()
class _RedirectStream(object):
_stream = None
def __init__(self, new_target):
self._new_target = new_target
# We use a list of old targets to make this CM re-entrant
self._old_targets = []
def __enter__(self):
self._old_targets.append(getattr(sys, self._stream))
setattr(sys, self._stream, self._new_target)
return self._new_target
def __exit__(self, exctype, excinst, exctb):
setattr(sys, self._stream, self._old_targets.pop())
class redirect_stdout(_RedirectStream):
"""Context manager for temporarily redirecting stdout to another file.
# How to send help() to stderr
with redirect_stdout(sys.stderr):
help(dir)
# How to write help() to a file
with open('help.txt', 'w') as f:
with redirect_stdout(f):
help(pow)
"""
_stream = "stdout"
class redirect_stderr(_RedirectStream):
"""Context manager for temporarily redirecting stderr to another file."""
_stream = "stderr"
class suppress(object):
"""Context manager to suppress specified exceptions
After the exception is suppressed, execution proceeds with the next
statement following the with statement.
with suppress(FileNotFoundError):
os.remove(somefile)
# Execution still resumes here if the file was already removed
"""
def __init__(self, *exceptions):
self._exceptions = exceptions
def __enter__(self):
pass
def __exit__(self, exctype, excinst, exctb):
# Unlike isinstance and issubclass, CPython exception handling
# currently only looks at the concrete type hierarchy (ignoring
# the instance and subclass checking hooks). While Guido considers
# that a bug rather than a feature, it's a fairly hard one to fix
# due to various internal implementation details. suppress provides
# the simpler issubclass based semantics, rather than trying to
# exactly reproduce the limitations of the CPython interpreter.
#
# See http://bugs.python.org/issue12029 for more details
return exctype is not None and issubclass(exctype, self._exceptions)
# Context manipulation is Python 3 only
_HAVE_EXCEPTION_CHAINING = sys.version_info[0] >= 3
if _HAVE_EXCEPTION_CHAINING:
def _make_context_fixer(frame_exc):
def _fix_exception_context(new_exc, old_exc):
# Context may not be correct, so find the end of the chain
while 1:
exc_context = new_exc.__context__
if exc_context is old_exc:
# Context is already set correctly (see issue 20317)
return
if exc_context is None or exc_context is frame_exc:
break
new_exc = exc_context
# Change the end of the chain to point to the exception
# we expect it to reference
new_exc.__context__ = old_exc
return _fix_exception_context
def _reraise_with_existing_context(exc_details):
try:
# bare "raise exc_details[1]" replaces our carefully
# set-up context
fixed_ctx = exc_details[1].__context__
raise exc_details[1]
except BaseException:
exc_details[1].__context__ = fixed_ctx
raise
else:
# No exception context in Python 2
def _make_context_fixer(frame_exc):
return lambda new_exc, old_exc: None
# Use 3 argument raise in Python 2,
# but use exec to avoid SyntaxError in Python 3
def _reraise_with_existing_context(exc_details):
exc_type, exc_value, exc_tb = exc_details
exec ("raise exc_type, exc_value, exc_tb")
# Handle old-style classes if they exist
try:
from types import InstanceType
except ImportError:
# Python 3 doesn't have old-style classes
_get_type = type
else:
# Need to handle old-style context managers on Python 2
def _get_type(obj):
obj_type = type(obj)
if obj_type is InstanceType:
return obj.__class__ # Old-style class
return obj_type # New-style class
# Inspired by discussions on http://bugs.python.org/issue13585
class ExitStack(object):
"""Context manager for dynamic management of a stack of exit callbacks
For example:
with ExitStack() as stack:
files = [stack.enter_context(open(fname)) for fname in filenames]
# All opened files will automatically be closed at the end of
# the with statement, even if attempts to open files later
# in the list raise an exception
"""
def __init__(self):
self._exit_callbacks = deque()
def pop_all(self):
"""Preserve the context stack by transferring it to a new instance"""
new_stack = type(self)()
new_stack._exit_callbacks = self._exit_callbacks
self._exit_callbacks = deque()
return new_stack
def _push_cm_exit(self, cm, cm_exit):
"""Helper to correctly register callbacks to __exit__ methods"""
def _exit_wrapper(*exc_details):
return cm_exit(cm, *exc_details)
_exit_wrapper.__self__ = cm
self.push(_exit_wrapper)
def push(self, exit):
"""Registers a callback with the standard __exit__ method signature
Can suppress exceptions the same way __exit__ methods can.
Also accepts any object with an __exit__ method (registering a call
to the method instead of the object itself)
"""
# We use an unbound method rather than a bound method to follow
# the standard lookup behaviour for special methods
_cb_type = _get_type(exit)
try:
exit_method = _cb_type.__exit__
except AttributeError:
# Not a context manager, so assume its a callable
self._exit_callbacks.append(exit)
else:
self._push_cm_exit(exit, exit_method)
return exit # Allow use as a decorator
def callback(self, callback, *args, **kwds):
"""Registers an arbitrary callback and arguments.
Cannot suppress exceptions.
"""
def _exit_wrapper(exc_type, exc, tb):
callback(*args, **kwds)
# We changed the signature, so using @wraps is not appropriate, but
# setting __wrapped__ may still help with introspection
_exit_wrapper.__wrapped__ = callback
self.push(_exit_wrapper)
return callback # Allow use as a decorator
def enter_context(self, cm):
"""Enters the supplied context manager
If successful, also pushes its __exit__ method as a callback and
returns the result of the __enter__ method.
"""
# We look up the special methods on the type to match the with statement
_cm_type = _get_type(cm)
_exit = _cm_type.__exit__
result = _cm_type.__enter__(cm)
self._push_cm_exit(cm, _exit)
return result
def close(self):
"""Immediately unwind the context stack"""
self.__exit__(None, None, None)
def __enter__(self):
return self
def __exit__(self, *exc_details):
received_exc = exc_details[0] is not None
# We manipulate the exception state so it behaves as though
# we were actually nesting multiple with statements
frame_exc = sys.exc_info()[1]
_fix_exception_context = _make_context_fixer(frame_exc)
# Callbacks are invoked in LIFO order to match the behaviour of
# nested context managers
suppressed_exc = False
pending_raise = False
while self._exit_callbacks:
cb = self._exit_callbacks.pop()
try:
if cb(*exc_details):
suppressed_exc = True
pending_raise = False
exc_details = (None, None, None)
except:
new_exc_details = sys.exc_info()
# simulate the stack of exceptions by setting the context
_fix_exception_context(new_exc_details[1], exc_details[1])
pending_raise = True
exc_details = new_exc_details
if pending_raise:
_reraise_with_existing_context(exc_details)
return received_exc and suppressed_exc
# Preserve backwards compatibility
class ContextStack(ExitStack):
"""Backwards compatibility alias for ExitStack"""
def __init__(self):
warnings.warn("ContextStack has been renamed to ExitStack",
DeprecationWarning)
super(ContextStack, self).__init__()
def register_exit(self, callback):
return self.push(callback)
def register(self, callback, *args, **kwds):
return self.callback(callback, *args, **kwds)
def preserve(self):
return self.pop_all()
|