what is the regular expression for identifying decimal number

Question

I have tried writing a code for identifying decimal number in python using regular expression as indicated in the below code.

It is working fine for many case but still failing to identify below inputs

import re
string = input()
r = re.compile(r"([+\-.]?\d*\.\d+)\b")
if(r.match(string)):
    print(True)
else: 
    print(False)

234.2344 ->for this input giving expected results

+.3456468 ->for this input giving expected results

5.34.0 -> for this input it should print False

4+345.0 -> for this input it should print False

You should add `^` at the start and `$` at the end. Without it, as long as the string **contains** a valid decimal pattern it will accept. You want to force it to capture the whole string — Tomerikoo, Jul 14 '19 at 16:02
@Tomerikoo: I have tried but it is not showing matching the decimal numbers. see below link https://regexr.com/4he9t — San, Jul 14 '19 at 16:59

Emma · Answer 1 · 2019-07-14T16:11:17.683

These expressions might likely validate integer and decimal numbers:

^[+-]?(?:\d+(?:\.\d+)?|\.\d+)$

or

^[+-]?(?:\d+(?:\.\d*)?|\.\d+)$

if for instance 1. would be valid.

DEMO 1

DEMO 2

Test

import re

regex = r"^[+-]?(?:\d+(?:\.\d+)?|\.\d+)$"

test_str = ("0.00000\n"
    "0.00\n"
    "-100\n"
    "+100\n"
    "-100.1\n"
    "+100.1\n"
    ".000\n"
    ".1\n"
    "3.\n"
    "4.")

print(re.findall(regex, test_str, re.MULTILINE))

Output

['0.00000', '0.00', '-100', '+100', '-100.1', '+100.1', '.000', '.1']

RegEx Circuit

jex.im visualizes regular expressions:

The expression is explained on the top right panel of this demo if you wish to explore/simplify/modify it.

score 1 · Answer 2 · answered Jul 14 '19 at 16:06

1

You can use

^[+-]?(?:\.\d+|\d+(?:\.\d+)?)$

Python demo|Regex Demo

answered Jul 14 '19 at 16:06

Code Maniac

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score 0 · Answer 3 · answered Jul 14 '19 at 16:05

Use beginning ^ and end anchors $ if you don't want it to match the first decimal-like part:

import re
decimal_re = re.compile(r'^\D?[+-]?\d*\.?\d+$')

cases = [
    '234.2344',
    '+.3456468',
    '5.34.0',
    '4+345.0',
    '1.5555',
    '.123123',
    '456.',
    '4.4.5.5'
]
for c in cases:
    print(decimal_re.match(c))

output:

<re.Match object; span=(0, 8), match='234.2344'>
<re.Match object; span=(0, 9), match='+.3456468'>
None
None
<re.Match object; span=(0, 6), match='1.5555'>
<re.Match object; span=(0, 7), match='.123123'>
None
None