diff options
| author | cinap_lenrek <cinap_lenrek@localhost> | 2011-05-03 11:25:13 +0000 |
|---|---|---|
| committer | cinap_lenrek <cinap_lenrek@localhost> | 2011-05-03 11:25:13 +0000 |
| commit | 458120dd40db6b4df55a4e96b650e16798ef06a0 (patch) | |
| tree | 8f82685be24fef97e715c6f5ca4c68d34d5074ee /sys/lib/python/contextlib.py | |
| parent | 3a742c699f6806c1145aea5149bf15de15a0afd7 (diff) | |
add hg and python
Diffstat (limited to 'sys/lib/python/contextlib.py')
| -rw-r--r-- | sys/lib/python/contextlib.py | 154 |
1 files changed, 154 insertions, 0 deletions
diff --git a/sys/lib/python/contextlib.py b/sys/lib/python/contextlib.py new file mode 100644 index 000000000..a807c42ce --- /dev/null +++ b/sys/lib/python/contextlib.py @@ -0,0 +1,154 @@ +"""Utilities for with-statement contexts. See PEP 343.""" + +import sys + +__all__ = ["contextmanager", "nested", "closing"] + +class GeneratorContextManager(object): + """Helper for @contextmanager decorator.""" + + def __init__(self, gen): + self.gen = gen + + def __enter__(self): + try: + return self.gen.next() + except StopIteration: + raise RuntimeError("generator didn't yield") + + def __exit__(self, type, value, traceback): + if type is None: + try: + self.gen.next() + except StopIteration: + return + else: + raise RuntimeError("generator didn't stop") + else: + try: + self.gen.throw(type, value, traceback) + raise RuntimeError("generator didn't stop after throw()") + except StopIteration, exc: + # Suppress the exception *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: + # 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> + + """ + def helper(*args, **kwds): + return GeneratorContextManager(func(*args, **kwds)) + try: + helper.__name__ = func.__name__ + helper.__doc__ = func.__doc__ + helper.__dict__ = func.__dict__ + except: + pass + return helper + + +@contextmanager +def nested(*managers): + """Support multiple context managers in a single with-statement. + + Code like this: + + with nested(A, B, C) as (X, Y, Z): + <body> + + is equivalent to this: + + with A as X: + with B as Y: + with C as Z: + <body> + + """ + exits = [] + vars = [] + exc = (None, None, None) + try: + try: + for mgr in managers: + exit = mgr.__exit__ + enter = mgr.__enter__ + vars.append(enter()) + exits.append(exit) + yield vars + except: + exc = sys.exc_info() + finally: + while exits: + exit = exits.pop() + try: + if exit(*exc): + exc = (None, None, None) + except: + exc = sys.exc_info() + if exc != (None, None, None): + # Don't rely on sys.exc_info() still containing + # the right information. Another exception may + # have been raised and caught by an exit method + raise exc[0], exc[1], exc[2] + + +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() |