I have three list A,B and C. I want to write the contents of the list to the file like this: A[1] B[1] C[1]
A[2] B[2] C[2] . . .
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Do you know for sure that these lists will have same number of elements? You probably want to serialize or save objects as CSV?Perpetualcoder– Perpetualcoder2011-03-04 19:19:18 +00:00Commented Mar 4, 2011 at 19:19
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I agree with @Daniel, some code snippet will help. I also think that @wheaties answered the question.Sam– Sam2011-03-04 19:24:05 +00:00Commented Mar 4, 2011 at 19:24
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4 Answers
Take a look at using zip. With zip you get a list of tuples, the tuples being the ith item of each list. As a bonus, the list of tuples is truncated to the shortest list of the three:
myComboList = zip(A, B, C)
Then you can always write the things in the order you'd like them without fear that one list may be shorter/longer than any of the others.
1 Comment
jack
It works but now how can I print it without ['u, because in a list,([u' added before the element. Can I use a for loop on this zip list?
I assume that the lengths of all lists are the same,
assert len(A) == len(B) == len(C)
for a, b, c in zip(A, B, C):
print a, b, c # replace with file write
Comments
If your lists are long, itertools.izip() will probably be your friend. File object .writelines() can consume the list, or you can insert a yield construct in between to do the formatting.
def format(seq):
for l in seq:
yield "%s %s %s" % l
f.writelines(format(itertools.izip(A, B, C)))
Taking idea of itertools.izip() from Bittrance ,
plus the fact that a built-in function format() already exists :
import itertools
A = ['arez','hgjkhg','jhdfg','uhireug']
B = ['aaa','bbb','cccc','ddd']
C = ['XXXX','YYYY','ZZZZ','WWWWW']
with open('zorgl.txt','w') as f:
f.writelines("[{0}] [{1}] [{2}]\n".format(*tu)
for tu in itertools.izip(A, B, C))
result in the file
[arez] [aaa] [XXXX]
[hgjkhg] [bbb] [YYYY]
[jhdfg] [cccc] [ZZZZ]
[uhireug] [ddd] [WWWWW]
And a revelation happened to me:
I had never realized that writelines() writes a sequence of strings, which can be an iterable, while write() writes only one string
Until now I was doing this kind of thing:
f.write('\n'.join(sequentia))
to write in a file.
But '\n'.join(sequentia) is an object that is created before being written in one time. I believe.
Comparatively, writelines() can receive an iterable, then the writing of lines can be done one line at a time. This allows to write progressively a big quantity of data in a file, while it could be harder to write the total amount of data in only one chunk at one time.
Am I right ?
The only little defect of writelines() is that it writes the strings as they are, without adding a newline.
So writelines(sequentz) writes the same as write(''.join(sequentz)) . Only write('\n'.join(sequentz)) adds a newline between elements
