I've made it a policy in my own code to always surround explicit calls to next() with try ... except StopIteration ... guards.
Otherwise if you don't guard the call and you get an unexpected exception from the next(), within a call chain that includes a for-loop over another generator, then that other for-loop will terminate without any error messages and the cause of its termination can be very difficult to track down.
Just to clarify here, the only time code raising a StopIteration will cause a for-loop to exit silently is if the StopIteration is raised in an __iter__ method, e.g.:
>>> def g(): ... raise StopIteration ... >>> class C(object): ... def __iter__(self): ... for i in range(3): ... yield i ... g() ... >>> for i in C(): ... print i ... 0 >>>
A StopIteration raised within the body of a for-loop will not cause it to terminate silently; the StopIteration exception will be propagated upward:
>>> def g(): ... raise StopIteration ... >>> def f(n): ... for i in range(n): ... print i ... g() ... >>> f(3) 0 Traceback (most recent call last): File "<interactive input>", line 1, in ? File "<interactive input>", line 4, in f File "<interactive input>", line 2, in g StopIteration >>>
Steve -- http://mail.python.org/mailman/listinfo/python-list
