Shi Mu wrote:
> In the follwoing code,
> Why the result is "'defenestrate', 'window', 'defenestrate', " before
> the original list instead of 'defenestrate', 'window', ?
>
>
>>>>a = ['defenestrate', 'cat', 'window', 'defenestrate']
>>>>for x in a[:]:
>
> ... if len(x) > 4: a.insert(0, x)
> ...
>
>>>>a
>
> ['defenestrate', 'window', 'defenestrate', 'defenestrate', 'cat',
> 'window', 'defenestrate']
>
The loop cycles over a *copy* of the list (that's what a[:] is, though
list(a) would also work), and adds any items it finds whose length is
greater that 4 at the start of the list, which starts out with four
elements in it.
So it adds "defenestrate" the first time through the loop, nothing the
second ("cat" is only three characters long), "window" the third and
"defenestrate" the fourth.
You can do a lot of this kind of playing at the interactive prompt,
which will answer your questions much more quickly!
For example, run the code with a could of print statements inserted:
>>> a = ['one111', 'two', 'three', 'four']
>>> for x in a[:]:
... print "x:", x
... if len(x) > 4: a.insert(0, x)
... print a
...
x: one111
['one111', 'one111', 'two', 'three', 'four']
x: two
['one111', 'one111', 'two', 'three', 'four']
x: three
['three', 'one111', 'one111', 'two', 'three', 'four']
x: four
['three', 'one111', 'one111', 'two', 'three', 'four']
>>>
regards
Steve
> On 10/25/05, Fredrik Lundh <[EMAIL PROTECTED]> wrote:
>
>>Shi Mu wrote:
>>
[about list comprehensions, explained by Fredrik]
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