I want to replace just the first occurrence of a regular expression in a string. Is there a convenient way to do this?
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2 Answers
re.sub() has a count parameter that indicates how many substitutions to perform. You can just set that to 1:
>>> s = "foo foo foofoo foo"
>>> re.sub("foo", "bar", s, 1)
'bar foo foofoo foo'
>>> s = "baz baz foo baz foo baz"
>>> re.sub("foo", "bar", s, 1)
'baz baz bar baz foo baz'
Edit: And a version with a compiled SRE object:
>>> s = "baz baz foo baz foo baz"
>>> r = re.compile("foo")
>>> r.sub("bar", s, 1)
'baz baz bar baz foo baz'
Comments
Specify the count argument in re.sub(pattern, repl, string[, count, flags])
The optional argument count is the maximum number of pattern occurrences to be replaced; count must be a non-negative integer. If omitted or zero, all occurrences will be replaced.
