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Regex {} question

Looking at this code https://code.sololearn.com/433/#py I don't understand, why changing line 3 to r"9{0,3}$" will not match "8" Since it's between 0 and 3 and "8" has zero "9" then it should match, right? What am I missing?

9/19/2020 6:11:22 AM

Nassim Abed

7 Answers

New Answer

+1

Nassim Abed don't you think an empty string will match 0 9's. You can also check by doing the below. import re pattern = r"89{0,3}$" if re.match(pattern, "8"): print("Match 1") if re.match(pattern, "899"): print("Match 2") if re.match(pattern, "8999"): print("Match 3")

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Your regex is explicitly looking for the number 9. Any other character will not match. Zero 9 is not 8

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How could you match 8 when the pattern is to just match 0 to 3 nines in the string.

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Ok then what exactly will match zero 9's?

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Use a range [1-8]{1,3} This will match any number between 1 and 8. You can change the range ( ex: change 1 to 0 to match numbers from 0 to 8) and the quantifiers to fit your needs.

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Thanks for the workaround. Workarounds aside, what is the syntax for matching zero repetitions? I am struggling to understand how Python deals with the logic of it. It seems so far that null is not zero, which is clear enough, but still doesn't answer the question: how to modify this code, what will match zero 9's without changing r"9{0,3}$"??

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:) Thank you Avinesh.