python iterating strings

Question

I am writing the content of "article" to a text file.

Source file:

lol hi
lol hello
lol text
lol test

Python:

for line in all_lines:
    if line.startswith('lol '):
        mystring = line.replace('lol ', '').lower().rstrip()

article = 'this is my saved file\n' + mystring + '\nthe end'

This is what gets saved to the txt file:

this is my saved file
test
the end

This is what I want saved to the txt file:

this is the saved file
hi
hello
test
text
the end

Simeon Visser · Accepted Answer · 2012-07-13 15:18:54Z

5

You are replacing the string each time. You will want to store the results of each lol line and then add them all to mystring:

mystring = []
for line in all_lines:
    if line.startswith('lol '):
        mystring.append(line.replace('lol ', '', 1).lower().rstrip() + '\n')

article = 'this is my saved file\n'+''.join(mystring)+'\nthe end'

In the above code, I've turned mystring into list which is then turned into a string at the end using the join method. Note that I've added a newline (\n) character to each line as you want that character in your output (and rstrip() removes it). Alternatively, you can write:

line.replace('lol ', '', 1).lower().rstrip(' ')

which lets rstrip() only strip spaces and not all other forms of whitespace.

Edit: An alternative approach is to write:

mystring.append(line.replace('lol ', '').lower().rstrip())

and:

article = 'this is my saved file\n'+'\n'.join(mystring)+'\nthe end'

edited Jul 13, 2012 at 15:18

answered Jul 13, 2012 at 15:12

Simeon Visser

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5 Comments

DSM Over a year ago

replace is a little dangerous here; replace('lol ','', 1) would prevent the possibility of an unintentional second replacement.

mgilson Over a year ago

@SimeonVisser -- I deleted my comment because it was incorrect. But I'm glad you added that alternative. (it's more clear to me anyway).

Simeon Visser Over a year ago

@mgilson: Why is it incorrect? Each line (except the last) will get a \n using join() and the last line will get it as well from '\nthe end'. Of course, it is not platform-independent code...

mgilson Over a year ago

@SimeonVisser -- your answer is completely correct. It was my comment which was wrong. (hence my deleting it).

jamylak Over a year ago

You could do this with one generator:

'this is my saved file\n' + ''.join(line.replace('lol ', '').lower() for line in all_lines if line.startswith('lol ')) + 'the end'

Hugh Bothwell · Accepted Answer · 2012-07-13 15:16:26Z

0

... or as a one-liner,

mystring = ''.join(line[4:].lower() for line in all_lines if line.startswith('lol '))

answered Jul 13, 2012 at 15:16

Hugh Bothwell

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Comments

jamylak · Accepted Answer · 2012-07-13 15:16:36Z

0

You could take this different approach:

with open('test.txt') as fin, open('out.txt', 'w') as fout:
    fout.write('this is my saved file\n')
    for line in fin:
        if line.startswith('lol '):
            fout.write(line.replace('lol ', '').lower())
    fout.write('the end')

answered Jul 13, 2012 at 15:16

jamylak

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