List Manipulation

[Bruno Desthuilliers]

Roman a écrit :

<ot>
Roman, please stop top-posting and learn to quote.
</ot>

> Bruno Desthuilliers wrote:
> 
>>Roman wrote:
>>(please dont top-post - corrected)
>>
>>>
>>>My intention is to create matrix based on parsed csv file. So, I
>>>would like to have a list of columns (which are also lists).
>>
>>csv = [
>>   ['L0C0', 'L0C1', 'L0C2'],
>>   ['L1C0', 'L1C1', 'L1C2'],
>>   ['L2C0', 'L2C1', 'L2C2'],
>> ]
>>
>>matrix = [[[] for l in range(len(csv))] for c in range(len(csv[0]))]
>>
>>for numline, line in enumerate(csv):
>>    for numcol, col in enumerate(line):
>>        matrix[numcol][numline] = col
>>
>>assert matrix == [
>>   ['L0C0', 'L1C0', 'L2C0'],
>>   ['L0C1', 'L1C1', 'L2C1'],
>>   ['L0C2', 'L1C2', 'L2C2']
>> ]
>>


 > Thanks for spending so much time  with me.  I had since made the
 > following change.
 >
 > matrix = [[[] for l in range(len(list(reader)[:10]))] for c in
 > range(len(list(reader)[7]))]

Technically; this won't work. The first call to list(reader) will 
consume reader.

It's also somewhat dumb (len(list(reader)[:10]) is always 10) and 
inefficient (you're calling list(reader) twice, when you could call it 
just once).

Instead of trying anything at random, read the fine manual and try to 
understand the example I gave you.

 > for numline, line in enumerate(reader):
 >    for numcol, col in enumerate(line):
 >        matrix[numcol][numline] = col
 >
 > print matrix
 >
 > I don't get mistakes anymore.  However, still nothing gets printed

If you don't print anything, nothing will be printed.