CODEWITHSUNDEEP
pythonlistsave
Frank White
Frank White

Reputation: 321

Looping over a list of lists and saving different files

I have a list in python with 4 elements that are all themselves lists of lines ( text)

I want to save those elements in numbered filenames.

for n in textblock:
    for line in textblock[n]:
        with open('file_{0}.dat'.format(n),'w') as ffile:
            ffile.write(textblock[n[line]])
            ffile.close()

I get the error message :

 for line in textblock[n]:
     TypeError: list indices must be integers, not list

Any hint what i can do to fix it ?

Upvotes: 2

Views: 1051

Answers (4)

Padraic Cunningham
Padraic Cunningham

Reputation: 180391

If you want to write lists of lists use the csv module:

import csv

for ind, lsts in enumerate(textblock):
    with open('file_{0}.dat'.format(ind),'w') as ffile:
        wr = csv.writer(file)
        wr.writerows(lsts)

Upvotes: 0

Matt Davidson
Matt Davidson

Reputation: 738

Let's clarify your data structure. It sounds like this:

outer_list = [ ["STRING1", "STRING2", ...],
               ["STRING1", "STRING2", ...],
               ["STRING1", "STRING2", ...],
               ["STRING1", "STRING2", ...]
             ]

So let's use python's iterable for loop structure to traverse the outer list.

for inner_list in outer_list:

But we want to write the contents of each inner_list to a file, using the position of the inner_list in the outer_list. Let's use the built in enumerate() function to get the position.

for n, inner_list in enumerate(outer_list, 1):
    # write inner list to file

Let's examine writing the inner_list to a file.

with open('file_{0}.dat'.format(n),'w') as ffile: # this is fine, well done.
    ffile.write(inner_list)

All together that would be:

for n, inner_list in enumerate(outer_list, 1):
    with open('file_{0}.dat'.format(n),'w') as ffile:
        ffile.write(inner_list)
        # no need to close the file, the with syntax does this for you.

EDIT: There is one more step needed here, as pointed out by @mhawke

The write() method requires it to be passed a string. We can convert our inner_list to a string quite easily. My preferred method would be to use the join() method. We can specify that we join each string in inner_list with a new line character, so that it will print nicely, i.e.

'\n'.join(inner_list)

Therefore our final solution would be:

for n, inner_list in enumerate(outer_list, 1):
    with open('file_{0}.dat'.format(n),'w') as ffile:
        ffile.write('\n'.join(inner_list))

Upvotes: 1

khelwood
khelwood

Reputation: 59095

If you are iterating through your textblock with for n in textblock:, then n will take the value of each item in textblock (so n is a list). Then if you try and get textblock[n], then you are trying to use the list n as an index.

You can just have:

for x in textblock:
    for line in x:
        # do stuff with the line

Don't try and close ffile -- it is closed automatically by the with block.

If you want to use the index in the file name, I think what you want is something like this:

for i, lines in enumerate(textblock):
    with open('file_{0}.dat'.format(i),'w') as ffile:
        for line in lines:
            ffile.write(line)

enumerate will give you the index and the items as you iterate through the list.

Upvotes: 1

itzMEonTV
itzMEonTV

Reputation: 20339

You can use enumerate

for n,m in enumerate(textblock, 1):
    with open('file_{0}.dat'.format(n),'w') as ffile:
        for line in m:
            ffile.write(line)

Note

  • with open will take care of close().
  • for i in [1,2,3] gives 1,2,3 in each iteration.No need of [1,2,3][i]

Upvotes: 1

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