os.walk walks too much
grey at despair.dmiyu.org
Fri Feb 27 23:32:25 CET 2004
On 2004-02-27, Marcello Pietrobon <teiffel at attglobal.net> wrote:
> Can I ask you one more thing ?
Sure. However I am a Python neophyte who happens to have a few years
experience so take everything I say with a large heaping of salt. :)
> It is surprizing to me that in
Ah, took me a minote to see what you were saying.
> for x in real[:]
> dirs[:] creates a copy of dirs
Well, creating a copy is the shorthand. What both of these are doing is
"output the values from the array x from y to z." Since y and z are not
specified you get the whole array (or string, or directory or any other
> dirs[:] =  - empty the original list
This is "assign the range of x to y the list given". A better way to see
it would be to do this:
= [1, 2, 3, 4]
[1, 2, 3, 4]
>>> foo[1:2] = [3, 2, 5]
[1, 3, 2, 5, 3, 4]
Hmmm, ok, even I'm scratching my head at that since I expected 1, 3, 2, 5
4. Erm, but you get the idea. :)
> dirs =  - empty a copy of the original list
This is because here you're assigning the name to a new object.
So in order...
for x in real[:] - iterate over the results of the slice of real from y to z.
foo = dirs[:] - Assign foo to the results of the slice of dirs from y to z.
dirs[:] =  - Assign the the area of dirs defined by slice y to z with an
dirs =  - Assign the name dirs to a new, empty array.
Where most people get hung up is the different between strings, which are
immutable, and lists/dictionaries, etc. which are mutable. :)
> I understand ( I think ) the concept of slicing, but this is stil
> surprizing to me. Like to say that when I do
> for x in real[:]
> this is not using slicing
Yes, it is. Take foo from above...
foo points to object 1075943980.
foo still points to object 1075943980.
However this is a different object, 1075943308.
So in the above example it is using a slice. real[:] is returning a slice
and it is that object which x is iterating over. Just because that slice
doesn't have a name assigned to it doesn't mean it doesn't exist. :)
> dirs[:] = 
> is using slicing
Well, it is using it in a different manner. Above you're using slicing to
tell Python what to return. Here you're using slicing to tell Python what to
> Maybe I just making a big mess in my mind.
> It looks like assignments in Python and C++ are pretty different
Never touched C++ so I cannot say. :)
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