How to replace multiple words of a string using regex in python?

Question

I have a dictionary like:

dic = { "xl": "xlarg", "l": "larg",'m':'medium'}

and I'd like to use re.sub or similar methods find any string (including a single letter) which are in dic.keys and replace it with the key's value.

def multiple_replace(dict, text):
     # Create a regular expression  from the dictionary keys
     regex = re.compile("(%s)" % "|".join(map(re.escape, dict.keys())))
    
     # For each match, look-up corresponding value in dictionary
     return regex.sub(lambda mo: dict[mo.string[mo.start():mo.end()]], text)

it works well for single letters in the string eg it changes size m to size medium but also it changes letters in words, eg changes monday to mediumonday

Thanks

Answer 1

You can use re.compile and the sub method to find the matching substrings and replace them. The idea here is that you join all of the keys into a single pattern by using an OR statement | . For each match you then use the matched substring to do a lookup on the replacement dict.

Along with this you can use a lookbehind and a lookahead regex. For the lookbehind, you want it to not be a word (?<!\\w) . For the lookahead, you want it to also not be word (?!\\w) .

Putting this altogether, we have: r"(?<!\\w)(xl|l|m)(?!\\w)"

Here's an example:

def replace_substrings(s, d):
    p = "|".join(d.keys())
    p = r"(?<!\w)(" + p + r")(?!\w)"
    return re.compile(p).sub(lambda m: d[m.group(0)], s)
...


dic = {"xl": "xlarg", "l": "larg",'m':'medium'}
inputs = [
    "size m",
    "monday",
    "xl sell",
    "m size m l xl",
]

for input in inputs:
    print(replace_substrings(input, dic))

This will output:

size medium
monday
xlarg sell
medium size medium larg xlarg