多行正则表达式替换

Question

I want to transform a text like:

$$
foo
bar
$$

to

<% tex
foo
bar
%>

and $\\alpha$ to <% tex \\alpha %> .

For the single line replace, I did this:

re.sub(r"\$(.*)\$", r"<% tex \1 %>", text)

...and it works fine.

Now, I added the multiline flag to catch the multiline one:

re.sub(r"(?i)\$\$(.*)\$\$", r"<% tex \1 %>", text)

...but it returns:

<% tex  %>
foo
bar
<% tex  %>

Why? I'm sure it's something trivial, but I can't imagine what.

Answer 1

I'd suggest using the re.M (multiline) flag, and gobbling up everything not a dollar sign in your capture.

>>> import re
>>> t = """$$
foo
bar
$$"""
>>> re.sub(r"\$\$([^\$]+)\$\$", r"<% tex \1 %>", t, re.M)
'<% tex \nfoo\nbar\n %>'

Answer 2

With python 2.7.12 I have verified that this will work:

>>> import re
>>> t = """$$
... foo
... bar
... $$"""
>>> re.sub(r"\$\$(.*?)\$\$", r"<% tex \1 %>", t, flags=re.DOTALL)
'<% tex \nfoo\nbar\n %>'

As for the DOTALL flag, according to the official document:

re.S

re.DOTALL

Make the '.' special character matches any character at all, including a newline; without this flag, '.' will match anything except a newline.