On 30/07/18 21:15, Rudy Matela wrote:
> Hello,
>
> Do you think it would be nice to allow with statements inside genexps or
> list comprehensions? The functions __enter__ and __exit__ would be
> automatically called as iterables are traversed. I am thinking of
> drafting a PEP about this. Examples:
>
>
> This
>
> g = (f.read() for fn in filenames with open(fn) as f)
>
> would be equivalent to the following use of a generator function:
>
> def __gen():
> for fn in filenames:
> with open(fn) as f:
> yield f.read()
> g = __gen()
To sail around Oscar's concern, this should rather be
def __gen():
for fn in filenames:
with open(fn) as f:
_v = f.read()
yield _v
But in this case I think it'd be clearer to make it an expression rather
than a generator expression term:
g = (f.read() with open(fn) as f for fn in filenames)
where
_ = f.read() with open(fn) as f
is equivalent to
with open(fn) as f:
_ = f.read()
Currently possibly (if silly) alternative:
from functools import wraps
class with_one_use:
def __init__(self, context):
self.__context = context
def __getattr__(self, name):
exc1 = False
obj = self.__context.__enter__()
try:
temp = getattr(obj, name)
except:
exc1 = True
if not self.__context.__exit__(*sys.exc_info()):
raise
else:
if callable(temp):
@wraps(temp)
def f(*args, **kwargs):
exc2 = False
try:
return temp(*args, **kwargs)
except:
exc2 = True
if not self.__context.__exit__(*sys.exc_info()):
raise
finally:
if not exc2:
self.__context.__exit__(None, None, None)
exc1 = True
return f
else:
return temp
finally:
if not exc1:
self.__context.__exit__(None, None, None)
g = (with_one_use(open(fn)).read() for fn in filenames)
-- Thomas
>
>
> This
>
> list = [f.read() for fn in filenames with open(fn) as f]
>
> would be equivalent to the following:
>
> list = []
> for fn in filenames:
> with open(fn) as f:
> list.append(f.read())
>
> --
> Rudy
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