cell and row

[Steve Holden]

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 <fredrik at pythonware.com> wrote:
> 
>>Shi Mu wrote:
>>
[about list comprehensions, explained by Fredrik]
-- 
Steve Holden       +44 150 684 7255  +1 800 494 3119
Holden Web LLC                     www.holdenweb.com
PyCon TX 2006                  www.python.org/pycon/