Terry J. Reedy added the comment:
Here is a test that now fails.
------------
from collections import deque
d = deque((0,))
old = []
try:
while True:
n = d.popleft()
old.append((n, len(d)))
if n < 5:
d.extend((n+1, n+2))
except IndexError:
pass
d = deque((0,))
new = []
for n in iter(d.popleft, exception=IndexError):
new.append((n, len(d)))
if n < 5:
d.extend((n+1, n+2))
assert new == old
--------
Here is Python code, partly from my python-ideas comments, that makes the test
pass. This version allows stopping on both a sentinel value and an exception
(or tuple thereof, I believe).
-------
__sentinel = object()
class callable_iterator:
class stop_exception: pass
def __init__(self, func, sentinel, exception):
self.func = func
self.sentinel = sentinel
if exception is not None:
self.stop_exception = exception
def __iter__(self):
return self
def __next__(self):
try:
x = self.func()
except self.stop_exception:
raise StopIteration from None
if x == self.sentinel:
raise StopIteration
else:
return x
def iter(it_func, sentinel=__sentinel, exception=None):
if sentinel == __sentinel and exception == None:
pass # do as at present
else:
return callable_iterator(it_func, sentinel, exception)
----------
stage: test needed -> needs patch
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Python tracker <[email protected]>
<http://bugs.python.org/issue20663>
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