How do I replace part of a large string in Python?

Question

I have a file with multiple lines, each having a long sequence of characters (no spaces).

For example in one line:

qwerrqweqweasdqweqwe*replacethistext*asdasdasd

qwerrqweqweasdqweqwe*withthistext*asdasdasd

The specific string I am looking for can happen any where in a certain line.

How would I accomplish this?

Thanks

how large is a large string? if we are talking about huge files, for example, then you will probably want to read the file in chunks, but your replacement algoritm will have to check if it is chunking inside a replace text. — ashwoods
– ashwoods, Commented May 18, 2011 at 2:13

Acorn · Accepted Answer · 2011-05-18 02:07:48Z

7

>>> s = 'qwerrqweqweasdqweqwe*replacethistext*asdasdasd'
>>> s.replace('*replacethistext*', '*withthistext*')
'qwerrqweqweasdqweqwe*withthistext*asdasdasd'

answered May 18, 2011 at 2:07

Acorn

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Borealid · Accepted Answer · 2011-05-18 02:05:32Z

1

import string
for line in file:
    print string.replace(line, "replacethistext", "withthistext")

answered May 18, 2011 at 2:05

Borealid

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2 Comments

Rafe Kettler Over a year ago

Ewww.... why wouldn't you use the method? You really should almost never have to import string.

John La Rooy Over a year ago

Only use this if you need to be backward compatible with Python1.x!

Rafe Kettler · Accepted Answer · 2011-05-18 02:06:14Z

1

line = "qwerrqweqweasdqweqwe*replacethistext*asdasdasd"
line = line.replace("*replacethistext*", "*withthistext*")

You can do this with any string. If you need substitutions with regexp, use re.sub(). Note that neither happens in place, so you'll have to assign the result to a variable (in this case, the original string).

With file IO and everything:

with open(filename, 'r+') as f:
    newlines = [] 
    for line in f:
        newlines.append(line.replace(old, new))
    # Do something with the new, edited lines, like write them to the file

answered May 18, 2011 at 2:06

Rafe Kettler

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Evan Cortens · Accepted Answer · 2011-05-18 02:06:26Z

1

fp = open(filename, 'r')
outfp = open(outfilename, 'w')
for line in fp:
    outfp.write(line.replace('*replacethistext*', '*withthistext*'))
fp.close()
outfp.close()

answered May 18, 2011 at 2:06

Evan Cortens

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