Python execute code only if for loop did not begin iteration (with generator)?
generator, python, python-2.7
Solution
I can't think of a better way than updating a boolean inside the for loop.
any_results = False
for x in g:
any_results = True
print x
if not any_results:
print 'Done'
Problem
The `else` block in a `for`/`else` clause gets executed if the iteration finishes but is not interrupted by `break`, so I read. Is there a language construct which would let me write something which executes only if the `for` loop did not begin iteration? If I was using a `tuple` or `list`, I would do something like this: ``` if seq: for x in seq: # something else: # something else ``` But when I use a generator, I don't get the behavior I want: ``` >>> g = (x for x in range(2)) >>> for x in g: ... print x ... else: ... print "done" ... 0 1 done # I don't want "done" here >>> g = (x for x in range(2) if x > 1) >>> if g: ... for x in g: ... print x ... else: ... print "done" ... >>> # I was expecting "done" here ``` How can I do this without exhausting creating a `tuple` or a `list` from the generator, while also using a `for` loop? I could use `next()` in a `while` loop and try to catch `StopIteration`, but I'd like to see if there's a nice way to do it with `for`.