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Python: using re.sub to replace multiple substrings multiple times

I am trying to fix text that has some very common scanning errors (I mistake for myself and vice versa). Basically I would like the replacement string to re.sub

depend on the number of times "I" is encountered, something like this:

re.sub("(\w+)(I+)(\w*)", "\g<1>l+\g<3>", "I am stiII here.")

What's the best way to achieve this?

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4 answers


Pass the function as a replacement string as described in. Your function can identify the error and create a better lookup based on that.

def replacement(match):
    if "I" in match.group(2):
        return match.group(1) + "l" * len(match.group(2)) + match.group(3)
    # Add additional cases here and as ORs in your regex

re.sub(r"(\w+)(II+)(\w*)", replacement, "I am stiII here.")
>>> I am still here.


(note that I changed your regex so that the repeated Is appears in the same group.)

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You can use lookaround instead I

, followed by or preceded by another I

:



print re.sub("(?<=I)I|I(?=I)", "l", "I am stiII here.")
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It seems to me that you can do something like:

def replace_L(match):
    return match.group(0).replace(match.group(1),'l'*len(match.group(1)))

string_I_want=re.sub(r'\w+(I+)\w*',replace_L,'I am stiII here.')
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Based on the answer suggested by DNS, I built something more sophisticated to catch all cases (or at least most of them), being careful not to add too many bugs:

def Irepl(matchobj):
    # Catch acronyms
    if matchobj.group(0).isupper():
        return matchobj.group(0)
    else:
        # Replace Group2 with 'l's
        return matchobj.group(1) + 'l'*len(matchobj.group(2)) + matchobj.group(3)


# Impossible to know if first letter is correct or not (possibly a name)
I_FOR_l_PATTERN = "([a-zA-HJ-Z]+?)(I+)(\w*)"
for line in lines:
    tmp_line = line.replace("l'", "I'").replace("'I", "'l").replace(" l ", " I ")
    tmp_line = re.sub("^l ", "I ", tmp_line)

    cor_line = re.sub(I_FOR_l_PATTERN, Irepl, tmp_line)

    # Loop to catch all errors in a word (iIIegaI for example)
    while cor_line != tmp_line:
        tmp_line = cor_line
        cor_line = re.sub(I_FOR_l_PATTERN, Irepl, tmp_line)

Hope this helps someone else!

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