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Comments on Python re.sub() how to include and slice the match in the substitution?
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Python re.sub() how to include and slice the match in the substitution?
I recently started learning regular expressions and I'm trying to use Python's re module, specifically the re.sub() function, to convert a subset of Markdown syntax to HTML whenever it appears in a string. However, I haven't been able to figure out how to slice the source string so that the Markdown syntax is removed.
For example, the string This is a *test* string. should get converted to This is a <i>test</i> string., but it keeps the asteriks like so: This is a <i>*test*</i> string.
This is my code (the regex checks for backslashes in case the syntax is escaped and is non-greedy in case of multiple matches):
testString = re.sub(r'(?<!\\)\*.*?\*(?!\\)', r'<i>\g<0></i>', testString)
I've tried splitting up the substitution and using string splicing like this r'<i>' + r'\g<0>'[1:-1] + r'</i>', but that just returns an italicized 'g'.
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To answer your immediate question, use a capture group.
re.sub(r'(?<!\\)\*(.*?)\*(?!\\)', r'<i>\g<1></i>', testString)
With that out of the way, text parsing for a language is probably best served by an existing library.
For instance, r'(?<!\\)\*(.*?)\*(?!\\)'
is probably meant to be r'(?<!\\)\*(.*?)(?!\\)\*',
but r'This is a *test\* string*' will still mess up what you think it should do.
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