On 6/30/10 8:50 PM, Mladen Gogala wrote:
x="quick brown fox jumps over a lazy dog"
y=''.join(list(x).reverse())
Traceback (most recent call last):
File "<stdin>", line 1, in<module>
TypeError
Why is TypeError being thrown? The reason for throwing the type error is
the fact that the internal expression evaluates to None and cannot,
therefore, be joined:
The "reverse" method, like "sort" and a couple others, are in-place
operations. Meaning, they do not return a new list but modify the
existing list. All methods that are "in-place" modifications return None
to indicate this. This way you can't make a mistake and think its
returning a sorted / reversed copy but it isn't.
However, you can easily get what you want by using the 'reversed'
function (and similarly, the 'sorted' function), a la:
>>> y = ''.join(reversed(list(x)))
The 'reversed' and 'sorted' functions are generators that lazilly
convert an iterable as needed.
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... Stephen Hansen
... Also: Ixokai
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