[Solved] Number divided by 4 by python regex

Question

You are misunderstanding what [...] does. They are character classes; if 1 character in that class matches, the text matches:

>>> import re
>>> re.search(r'[32]', '3')
<_sre.SRE_Match object; span=(0, 1), match="3">
>>> re.search(r'[32]', '2')
<_sre.SRE_Match object; span=(0, 1), match="2">

Don’t use a character class when you only want to match literal text.

The following would only match your specific 2-digit patterns:

r = re.compile('^([048]$)|(-?[0-9]*(12|16|20|24|28|32|36|40|44|48|52|56|60|64|68|72|76|80|84|88|92|96)$)')

This works as expected:

>>> r = re.compile('^([048]$)|(-?[0-9]*(12|16|20|24|28|32|36|40|44|48|52|56|60|64|68|72|76|80|84|88|92|96)$)')
>>> r.search("32")
<_sre.SRE_Match object; span=(0, 2), match="32">
>>> r.search("33")
>>> r.search("33") is None
True

You are not matching numbers ending in 00 however (like 100, 200, etc.), which are also divisible by 4.

Note that the expression can be reduced further; the digits 0, 4 and 8 only follow even numbers while the digits 2 and 6 always follow odd numbers:

r = re.compile('^-?(?:[048]|[0-9]*(?:[02468][048]|[13579][26]))$')

I moved the - sign check out to apply to all numbers.

Accepted Answer