On 4/1/2010 7:20 PM, Andrew Svetlov wrote:
using of copy.copy for simple iterators is forbidden
import copy
copy.copy(iter([1, 2, 3]))
Traceback (most recent call last):
File "<stdin>", line 1, in<module>
File "/home/andrew/projects/py3k/Lib/copy.py", line 96, in copy
return _reconstruct(x, rv, 0)
File "/home/andrew/projects/py3k/Lib/copy.py", line 284, in _reconstruct
y = callable(*args)
File "/home/andrew/projects/py3k/Lib/copyreg.py", line 88, in __newobj__
return cls.__new__(cls, *args)
TypeError: object.__new__(list_iterator) is not safe, use
list_iterator.__new__()
The same happens for the iterators of other builtin classes: tuples,
sets, and dicts (that I tried). In the other hand,
>>> copy.copy(iter(range(1,3,1))) # 3.1
Traceback (most recent call last):
...
TypeError: rangeiter() requires 3 int arguments
and similar for filter and map.
I do not know whether the former group is detected by rule or explicit
hard-coded list, but I suspect the latter.
That behavior is safe and clean.
But it's possible to copy iterator objects returned by itertools functions:
i = itertools.chain([1, 2], [3, 4, 5])
i.__next__()
1
j = copy.copy(i)
This works because itertools.chain() is legal
j.__next__()
Traceback (most recent call last):
File "<stdin>", line 1, in<module>
StopIteration
Because itertools.chain() is empty.
i.__next__()
2
Looks like itertools object should be protected from usage like that.
I suspect only those for which itertools.xxx() works rather than raising
an exception.
Folks, what are you think about?
Why privilige the itertools module? A possible rule would be to not copy
anything with both .__iter__ and .__next__.
Terry Jan Reedy
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