Question

I am trying to write a regular expression that will match all cases of

[[any text or char her]]

in a series of text.

Eg:

My name is [[Sean]]
There is a [[new and cool]] thing here.

This all works fine using my regex.

data = "this is my tes string [[ that does some matching ]] then returns."
p = re.compile("\[\[(.*)\]\]")
data = p.sub('STAR', data)

The problem is when I have multiple instances of the match occuring :[[hello]] and [[bye]]

Eg:

data = "this is my new string it contains [[hello]] and [[bye]] and nothing else"
p = re.compile("\[\[(.*)\]\]")
data = p.sub('STAR', data)

This will match the opening bracket of hello and the closing bracket of bye. I want it to replace them both.

Answer 1

.* is greedy and matches as much text as it can, including ]] and [[, so it plows on through your “tag” boundaries.

A quick solution is to make the star lazy by adding a ?:

p = re.compile(r"\[\[(.*?)\]\]")

A better (more robust and explicit but slightly slower) solution is to make it clear that we cannot match across tag boundaries:

p = re.compile(r"\[\[((?:(?!\]\]).)*)\]\]")

Explanation:

\[\[        # Match [[
(           # Match and capture...
 (?:        # ...the following regex:
  (?!\]\])  # (only if we're not at the start of the sequence ]]
  .         # any character
 )*         # Repeat any number of times
)           # End of capturing group
\]\]        # Match ]]