Question

How I can extract {{template|{{template2}}|other params}} from this string if we just know “template”:

{{template0}}
{{template|{{template2}}|other params}}
{{template3}}

Answer 1

This should do what you want:

>>> match = re.search(r'^{{template\b.*$', your_string, re.M)
>>> match.group()
'{{template|{{template2}}|other params}}'

It uses a word boundary (\b) after ‘template’ so it will not match ‘template0’ or ‘template3’. The re.M option is used so ^ and $ will match the beginnings and ends of lines, instead of the beginning and end of the string.

Edit: Try the following regex for the newline case from your comment:

r'^{{template\b(?:[^}]\n+|\n+[^{]|.)*$'

This should work whether you put the newline before or after the |.

Edit 2: It is very important with regex questions that you specify what the input can look like up front. Here is another version that works with the text from your latest comment:

r'^{{template\b(?:[^}\n]\n+|\n+[^{\n]|.)*}}$'

Now it will handle multiple newlines correctly, and I added the }} at the end in case your match is the last bracketed group before lines with other formats.