RegEx validation of decimal numbers with comma or dot

Question

How to validate such number input with one RegEx. Strings are not allowed. Two decimal positions after dot or comma.

Example:

123.34
1.2

Answer 1

pat = re.compile('^\d+([\.,]\d\d)?$')
re.match(pat, '1212')
<_sre.SRE_Match object at 0x91014a0>
re.match(pat, '1212,1231')
None
re.match(pat, '1212,12')
<_sre.SRE_Match object at 0x91015a0>