On 04/08/2012 20:20, Franck Ditter wrote:
Two similar iterable objects but with a different behavior :
$$$ i = range(2,5)
$$$ for x in i : print(x,end=' ')
2 3 4
$$$ for x in i : print(x,end=' ') # i is not exhausted
2 3 4
--------- Compare with :
$$$ i = filter(lambda c : c.isdigit(), 'a1b2c3')
$$$ for x in i : print(x,end=' ')
1 2 3
$$$ for x in i : print(x,end=' ') # i is exhausted
$$$
IMHO, this should not happen in Py3k.
What is the rationale of this (bad ?) design, which forces the programmer
to memorize which one is exhaustable and which one is not ?...
'range' returns a 'range' object:
>>> i = range(2,5)
>>> i
range(2, 5)
The 'for' loop passes it to 'iter' to get an iterator:
>>> iter(i)
<range_iterator object at 0x0135DB30>
More importantly:
>>> iter(i) is i
False
In other words, when asked for an iterator, the 'range' object always
creates a new one.
On the other hand, 'filter' returns a 'filter' object:
>>> i = filter(lambda c : c.isdigit(), 'a1b2c3')
>>> i
<filter object at 0x01360B30>
The 'for' loop passes it to 'iter' to get an iterator:
>>> iter(i)
<filter object at 0x01360B30>
More importantly:
>>> iter(i) is i
True
In other words, the 'filter' object returns _itself_ as the iterator.
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