On 20May2015 16:20, Daniel Gonçalves <daniel.ba...@gmail.com> wrote:
When you decorate a function with contextmanager that didn't yield you got an
AttributeError instead of a proper RuntimeError "generator didn't yield". For
example:
@contextlib.contextmanager
def foo():
... pass
...
with foo():
... do_something()
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python2.7/contextlib.py", line 17, in __enter__
return self.gen.next()
AttributeError: 'NoneType' object has no attribute 'next'
The proper exception should be a RuntimerError with the "generator didn't
yield" message. At least for Python version 2.7.6.
Unfortunately no.
Your function foo() is _not_ a generator because it does not have a yield
statement. Therefore it is a normal funcion which returns None (because it also
lacks a return statement).
contextlib.contextmanager works by _calling_ the inner foo(). It expected to
get a generator back. But your foo() returns None, _not_ a generator.
hence the error message: contextlib.contextmanager tries to use the return
value with next(), which of course fails with exactly the exception one might
expect.
To get "generator didn't yield" you need to actually have a generator. Eg:
@contextlib.contextmanager
def foo():
if false:
yield
Untested, though.
Cheers,
Cameron Simpson <c...@zip.com.au>
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