Regular Expressions 101

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'''
(\w+)([ ](\1))+
'''
msg
1st Capturing Group
(\w+)
\w
matches any word character (equivalent to [a-zA-Z0-9_])
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
2nd Capturing Group
([ ](\1))+
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you're not interested in the data
Match a single character present in the list below
[ ]
matches the character with index 3210 (2016 or 408) literally (case sensitive)
3rd Capturing Group
(\1)
\1 matches the same text as most recently matched by the 1st capturing group
Global pattern flags
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
s modifier: single line. Dot matches newline characters
g modifier: global. All matches (don't return after first match)
Your regular expression does not match the subject string.

Regular Expression
No Match

r'''
'''
msg

Test String

Substitution

Processing...