Using re.sub and replacing string WITH a regular expression using variables in Python

Question

Suppose I have a string

the_string = "the brown fox"

And I wan't to replace the spaces with a number of characters, for example, 5 dash marks

new_string = "the-----brown-----fox"

but this will be a variable, so i cant just do:

the_string = 'the brown fox'
new_string = re.sub(r'\s', '-----', the_string)

I need something like the following:

the_string = 'the brown fox'
num_dashes = 5
new_string = re.sub(r'\s', r'-{num_dashes}', the_string)

Is something like this possible?

Is there some reason you do not want to use str.replace(old, new[, count])? You could write new_string = the_string.replace(' ', '-' * num_dashes). — Noctis Skytower
– Noctis Skytower, Commented Aug 18, 2015 at 20:35
In this case that would work just fine. Does str.replace work with a regex? For example if I need to replace one or more spaces. Could be one, could be multiple. — Eddie
– Eddie, Commented Aug 19, 2015 at 5:58
Then you are correct. You would want to use the re module for a variable number of whitespace characters. The str.replace method does not work with regular expressions. — Noctis Skytower
– Noctis Skytower, Commented Aug 19, 2015 at 13:02

user156213 · Accepted Answer · 2015-08-18 19:44:00Z

3

Yes, you can do this:

the_string = 'the brown fox'
num_dashes = 5
re.sub(r'\s', '-'*num_dashes, the_string)

answered Aug 18, 2015 at 19:44

user156213

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vks · Accepted Answer · 2015-08-18 19:43:09Z

2

def repl(matchobj):
    if matchobj.group():
        #do something
        #return whatever you want to replace

my_str = "the brown fox"

pattern = r"\s+"
print re.sub(pattern, repl, my_str)

You can define a function in re.sub

answered Aug 18, 2015 at 19:43

vks

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1 Comment

Anwarvic Over a year ago

That's genius, THANKS A LOT

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