Regular Expressions 101

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"
(http(s)?:\/\/.)?(www\.)?[-a-zA-Z0-9@:%._\+~#=]{2,256}\.[a-z]{2,6}\b([-a-zA-Z0-9@:%_\+.~#?&//=]*)
"
gm
1st Capturing Group
(http(s)?:\/\/.)?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
http
matches the characters http literally (case sensitive)
2nd Capturing Group
(s)?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
s matches the character s with index 11510 (7316 or 1638) literally (case sensitive)
: matches the character : with index 5810 (3A16 or 728) literally (case sensitive)
\/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
\/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
. matches any character (except for line terminators)
3rd Capturing Group
(www\.)?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
www
matches the characters www literally (case sensitive)
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
Match a single character present in the list below
[-a-zA-Z0-9@:%._\+~#=]
{2,256} matches the previous token between 2 and 256 times, as many times as possible, giving back as needed (greedy)
- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
a-z matches a single character in the range between a (index 97) and z (index 122) (case sensitive)
A-Z matches a single character in the range between A (index 65) and Z (index 90) (case sensitive)
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
@:%._
matches a single character in the list @:%._ (case sensitive)
\+ matches the character + with index 4310 (2B16 or 538) literally (case sensitive)
~#=
matches a single character in the list ~#= (case sensitive)
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
Match a single character present in the list below
[a-z]
{2,6} matches the previous token between 2 and 6 times, as many times as possible, giving back as needed (greedy)
a-z matches a single character in the range between a (index 97) and z (index 122) (case sensitive)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
4th Capturing Group
([-a-zA-Z0-9@:%_\+.~#?&//=]*)
Match a single character present in the list below
[-a-zA-Z0-9@:%_\+.~#?&//=]
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
a-z matches a single character in the range between a (index 97) and z (index 122) (case sensitive)
A-Z matches a single character in the range between A (index 65) and Z (index 90) (case sensitive)
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
@:%_
matches a single character in the list @:%_ (case sensitive)
\+ matches the character + with index 4310 (2B16 or 538) literally (case sensitive)
.~#?&//=
matches a single character in the list .~#?&/= (case sensitive)
Global pattern flags
g modifier: global. All matches (don't return after first match)
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
Your regular expression does not match the subject string.

Regular Expression
No Match

r"
"
gm

Test String