Python:how to replace string by index

Question

I am writing a program like unix tr, which can replace string of input. My strategy is to find all indexes of source strings at first, and then replace them by target strings. I don't know how to replace string by index, so I just use the slice. However, if the length of target string doesn't equal to the source string, this program will be wrong. I want to know what's the way to replace string by index.

def tr(srcstr,dststr,string):
    indexes = list(find_all(string,srcstr)) #find all src indexes as list
    for index in indexes:
        string = string[:index]+dststr+string[index+len(srcstr):]
    print string

tr('aa','mm','aabbccaa')
the result of this will be right: mmbbccmm
but if tr('aa','ooo','aabbccaa'), the output will be wrong:

ooobbcoooa

Manish · Accepted Answer · 2012-03-02 07:35:32Z

3

Python strings are immutable (as far as I can remember), so you can't just go in and insert stuff.

Luckily Python already has a replace() function.

>>> s = "hello, world!"
>>> s1 = s.replace("l", "k")
>>> print s1
hekko, workd!

edited Mar 2, 2012 at 7:35

answered Mar 2, 2012 at 7:30

Manish

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1 Comment

Taymon Over a year ago

@remy Has your question been answered? If so, you can accept an answer using the green check mark.

Eli Stevens · Accepted Answer · 2012-03-02 07:26:35Z

0

Are you aware of the str.replace method? I think it will do what you're wanting:

http://docs.python.org/library/string.html#string.replace

And when you find that you're wanting to support more than simple string replacement, check out the re module:

http://docs.python.org/library/re.html

answered Mar 2, 2012 at 7:26

Eli Stevens

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Comments

Fred · Accepted Answer · 2012-03-02 08:03:23Z

0

def tr(srctr, deststr, string):
    string = string.split(srctr)
    return ''.join([deststr if i == '' else i for i in string ])

print tr('aa', 'ooo', 'aabbccaa') # ooobbccooo

answered Mar 2, 2012 at 8:03

Fred

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