Vedran Furac( wrote: > Hi! > > In [69]: a = 'a b c' > In [70]: b = 'a b, c d' > > In [74]: [i for i in a.split() if i not in b.split()] > Out[74]: ['b'] > > Everything ok. > > In [77]: b.split() == [i for i in b.split()] > Out[77]: True > > As expected. Now, put this in the first list comprehension: > > In [80]: [i for i in a.split() if i not in [i for i in b.split()] ] > Out[80]: ['d'] > > Hmmmm... why is that?
>>> a = "abc" >>> b = "a b, c d".split() >>> b ['a', 'b,', 'c', 'd'] >>> [i for i in a if i not in b] ['b'] As expected, so far, but now comes the critical step: >>> [i for i in a if i not in [i for i in b]] ['d'] The problem is that list comprehensions do not introduce a new namespace. So the inner and the outer list comp share the same i. You can either rename the inner i >>> [i for i in a if i not in [k for k in b]] ['b'] or use a generator expression which does give a new namespace: >>> list(x for x in "abc") ['a', 'b', 'c'] >>> x Traceback (most recent call last): File "<stdin>", line 1, in <module> NameError: name 'x' is not defined >>> [i for i in a if i not in (i for i in b)] ['b'] Peter -- http://mail.python.org/mailman/listinfo/python-list
