Question

I am trying to learn regular expressions by writing something akin to latex2html in Python. But I am having a hard time figuring out how to match latex equations — things of the form $ … $ where … can be any expression in LaTeX, while allowing for escape sequences at the same time.

In other words, the problem case is $\$$. I want the regular expression to match on $\$$, rather than just $\$.

Answer 1

You can use negative lookbehind to make sure you don’t match \$. something like:

\\$.*?(?<!\\\\)\\$

E.g.

print re.findall("\\$.*?(?<!\\\\)\\$", "$x= \$12$ and $x=12$")

will find two matches: $x= \$12$ and $x=12$