daedae11 wrote:
The build-in function reversed() in Python2.5 returns a iterator. But I don't
know how to use the iterator.
Please give me a simple example about how to use bulid-in function reversed()
to reverse a list.
You use the iterator the same way you would any other iterator:
* in for loops:
for obj in reversed(my_list):
print(obj)
* pass it to functions which expect an iterator:
a = reduce(function, reversed(my_list))
b = map(func, reversed(my_string))
* create a new sequence:
my_list = list(reversed(my_list))
Note that the advantage of reversed is that it is lazy (it returns an
iterator). If you just want a copy of a list in reverse order, you can use
slicing:
my_list[::-1]
(also works on strings and tuples).
If you want to reverse the list in place, instead of making a copy:
my_list.reverse() # must be a list, not strings or tuples
reversed() is more general: it can work on any finite iterable object, not
just lists.
--
Steven
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