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In Python I can do
import re
re.match("m", "mark")
and I get the expected result:
<_sre.SRE_Match object; span=(0, 1), match='m'>
But it only works if the pattern is at the start of the string:
re.match("m", "amark")
gives None. There is noting about that pattern which requires it to be at the start of the string - no ^ or similar. Indeed it works as expected on regex101.
Does Python have some special behaviour - and how do I disable it please?
852
Basically (0+1)* mathes any sequence of ones and zeroes. So, in your example (0+1)*1(0+1)* should match any sequence that has 1. It would not match 000 , but it would match 010 , 1 , 111 etc. (0+1) means 0 OR 1. 1* means any number of ones.
You make it non-greedy by using ". *?" When using the latter construct, the regex engine will, at every step it matches text into the "." attempt to match whatever make come after the ". *?" . This means that if for instance nothing comes after the ".
Practical Data Science using Python , '*' or '+' are called repeating character classes. If you repeat a character class by using the '?' , '*' or '+' operators, you will repeat the entire character class, and not just the character that it matched. The regex '[0-9]+' can match '579' as well as '333'.
From the docs on re.match:
If zero or more characters at the beginning of
stringmatch the regular expressionpattern, return a corresponding match object.
Use re.search to search the entire string.
The docs even grant this issue its own chapter, outlining the differences between the two: search() vs. match()
78
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