Extract all substrings between two markers

Question

I have a string:

mystr = "&marker1\nThe String that I want /\n&marker1\nAnother string that I want /\n"

What I want is a list of substrings between the markers start="&maker1" and end="/\n". Thus, the expected result is:

whatIwant = ["The String that I want", "Another string that I want"]

I've read the answers here:

And tried this but not successfully,

>>> import re >>> mystr = "&marker1\nThe String that I want /\n&marker1\nAnother string that I want /\n" >>> whatIwant = re.search("&marker1(.*)/\n", mystr) >>> whatIwant.group(1) Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'NoneType' object has no attribute 'group'

What could I do to resolve this? Also, I have a very long string

>>> len(myactualstring) 7792818

Daweo · Accepted Answer · 2020-06-12 10:56:01Z

What could I do to resolve this? I would do:

import re mystr = "&marker1\nThe String that I want /\n&marker1\nAnother string that I want /\n" found = re.findall(r"\&marker1\n(.*?)/\n", mystr) print(found)

Output:

['The String that I want ', 'Another string that I want ']

Note that:

& has special meaning in re patterns, if you want literal & you need to escape it (\&)
. does match anything except newlines
findall is better suited choiced if you just want list of matched substrings, rather than search
*? is non-greedy, in this case .* would work too, because . do not match newline, but in other cases you might ending matching more than you wish
I used so-called raw-string (r-prefixed) to make escaping easier

Read module re documentation for discussion of raw-string usage and implicit list of characters with special meaning.

Is there a limit on the string length which can be process by regular expressions module?

Tim Biegeleisen · Accepted Answer · 2020-06-12 10:47:01Z

Consider this option using re.findall:

mystr = "&marker1\nThe String that I want /\n&marker1\nAnother string that I want /\n" matches = re.findall(r'&marker1\n(.*?)\s*/\n', mystr) print(matches)

This prints:

['The String that I want', 'Another string that I want']

Here is an explanation of the regex pattern:

&marker1 match a marker \n newline (.*?) match AND capture all content until reaching the first \s* optional whitespace, followed by /\n / and newline

Note that re.findall will only capture what appears in the (...) capture group, which is what you are trying to extract.

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