Issue 1328959: Empty Generator doesn't evaluate as False (original) (raw)
Issue1328959
Created on 2005-10-17 20:26 by docwhat, last changed 2022-04-11 14:56 by admin. This issue is now closed.
| Messages (2) | ||
|---|---|---|
| msg26614 - (view) | Author: Christian Höltje (docwhat) | Date: 2005-10-17 20:26 |
| The following code doesn't work correctly if the function "generator()" doesn't have any values. if generator(): print "This should only happen when the generator runs yield" print " but it is always true, even if the generator is empty" else: print "this is the expected path when the generator is empty" The workaround is: try: generator().next() print "this is the true case" except StopIteration: print "this is the false case" This means that generators are not transparent and they don't behave as expected (like a list or tuple). I've been bitten by this enough that I am unhappy. :-( | ||
| msg26615 - (view) | Author: Raymond Hettinger (rhettinger) *  |
Date: 2005-10-17 20:58 |
| Logged In: YES user_id=80475 Your unhappiness is predicated on an invalid set of assumptions. For most generators, it is not possible to know in advance whether the iterator will raise StopIteration on the next call. Also, Guido has pronounced that generators (like most objects) will always evaluate to True. |
| History | |||
|---|---|---|---|
| Date | User | Action | Args |
| 2022-04-11 14:56:13 | admin | set | github: 42496 |
| 2005-10-17 20:26:20 | docwhat | create |