@contextlib question

[Peter Otten]

Neal Becker wrote:

> http://www.python.org/doc/2.5.2/lib/module-contextlib.html has this
> example: from contextlib import contextmanager
> 
> @contextmanager
> def tag(name):
>     print "<%s>" % name
>     yield
>     print "</%s>" % name
> 
> contexlib.contextmanager doc string (2.5.1) says:
>     Typical usage:
>     
>         @contextmanager
>         def some_generator(<arguments>):
>             <setup>
>             try:
>                 yield <value>
>             finally:
>                 <cleanup>
>     
>  Should I use the 'try', and 'finally' as in the 2nd example, or should I
>  use the first example?  Does it matter?
> 

These examples are basically the same. try...finally does what it always
does -- ensure that the cleanup code is executed even if an exception
occurs in the try block. So

with some_generator(...):
    1/0

will execute <cleanup> whereas

with tag("yadda"):
    1/0

will print <yadda> but not </yadda>. (Both will raise the ZeroDivisionError)

Peter