Formatting data using python

Question

I would like to parse the data with 'tab delimited' and would like to replace certain string in the data.

input file: vi foo.txt:

Bob lives in%3a Boston
Sam lives    in Houston
Jay       lives in Ruston
Bill        lives in           Atlanta

This is what I came up with: vi foo.py:

import re

fin = open("foo.txt")
fout =  open("bar.txt", "w")
for line in fin.readlines():
    fout.write('\t'.join(line.split())+'\n') # parse data with tab delimited

for line in fin.readlines():
    fout.write(re.sub('%3a',':',line)) # substitute string with regex

vi bar.txt:

Bob lives   in%3a   Boston
Sam lives   in  Houston
Jay lives   in  Ruston
Bill    lives   in  Atlanta

Why is %3a still in output rather than ':'?

Thanks,

Rio

I dont know what you are looking to do with 2 loops, but you need to reset the file pointer before the second loop with a fin.seek(0) , then you will see 8 lines instead of 4 - the first set would have %3a, and second would have a : — karthikr
– karthikr, Commented Sep 14, 2014 at 17:43

tktk · Accepted Answer · 2014-09-14 17:43:59Z

3

readlines() is an iterator. Once you consume it - it's no more. You are consuming it on the first call to for line in fin.readlines():. On the second call - there's nothing to iterate over anymore, so this line: fout.write(re.sub('%3a',':',line)) is never called.

Even if it did - it would have created two copies of the input data in the output - one tab delimited but with %3a, and one not tab delimited but without %3a.

What you want to do is this:

for line in fin.readlines():
    fout.write('\t'.join(re.sub('%3a',':',line).split())+'\n')

answered Sep 14, 2014 at 17:43

tktk

11.8k8 gold badges61 silver badges75 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

stanleyxu2005 Over a year ago

I did not see he's called readlines() twice. Your answer is correct. And by the way, re is too heavy for a simple string replacing in his case.

Rio Over a year ago

Thanks! How can I achieve it with 2 for loops as I tried before? I want the code to be more readable and I have many strings to substitute.

tktk Over a year ago

@stanleyxu2005 This might be true, but it's not the epitome of the issues with his code.

tktk Over a year ago

@Rio I don't tink that more loops are more readable - on the contrary. However, if you do want to implement more than one loop - you need each loop to take as input the output of the loops before that.

Rio Over a year ago

If I have multiple patterns to be replaced e.g. %3a as :, %3f as ? how can I achieve it? Thanks

Collectives™ on Stack Overflow

Formatting data using python

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related