0

I don't understand the result of this python regular expression "re.match("([abc])+", "abc")". Can anybody explain how this regex works step by step?

import re
m = re.match("([abc])+", "abc")
print(m.groupdict())
print(m.groups())
print(m.group(1))

{} ('c',) c

I expected the result of m.group(1) will be "a".

iregex
  • 1
  • 1
    What's you actual intent? It's a little odd to be `+`-repeating a group. Typically that is done after the character class and inside of the group, not outside. – Reinderien Aug 14 '23 at 04:15

1 Answers1

-2

The regular expression "([abc])+" is attempting to match and capture consecutive occurrences of characters 'a', 'b', or 'c' in the string "abc". Let's break down how the regex works step by step:

"([abc])+":

([abc]): This is a capturing group that matches a single character that is either 'a', 'b', or 'c'. +: This quantifier specifies that the capturing group should match one or more occurrences of the characters 'a', 'b', or 'c'. "abc": The input string you're trying to match.

Here's how the matching process unfolds:

The regex engine starts by trying to match the pattern "([abc])+" against the string "abc".

The capturing group ([abc]) matches the first character 'a'.

The quantifier + then tries to match more characters. It matches the next character 'b'.

The quantifier + continues and matches the final character 'c'.

The regex engine has successfully matched the entire string "abc" against the pattern "([abc])+".

As a result, the captured group contents are as follows:

m.groupdict(): This method returns a dictionary of named capturing groups. Since there are no named groups in the regex, an empty dictionary is returned: {}. m.groups(): This method returns a tuple containing all the captured groups, including nested groups. In this case, it returns ('c',) because the last matched character 'c' is captured. m.group(1): This method returns the contents of the first capturing group. Since the capturing group captured three characters 'a', 'b', and 'c', the last captured character 'c' is returned. The result of m.group(1) is 'c', not 'a', because the capturing group captures each occurrence of characters 'a', 'b', or 'c' and the last one captured is 'c'.

If you want to capture the entire matched substring "abc" as a single group, you can modify the regex like this: "([abc]+)". This will capture the entire sequence of consecutive characters 'a', 'b', and 'c'.

eashwar natarajan
  • 45
  • 6