I'm learning regex and I would like to use a regular expression in Python to define only integers - whole numbers but not decimals.
I could make one that only allows numbers by using \d, but it also allows decimal numbers, which I don't want:
price = TextField(_('Price'), [
validators.Regexp('\d', message=_('This is not an integer number, please see the example and try again')),
validators.Optional()])
How can I change the code to only allow integers?
Regexp work on the character base, and \d means a single digit 0...9 and not a decimal number.
A regular expression that matches only integers with a sign could be for example
^[-+]?[0-9]+$
meaning
^ - start of string[-+]? - an optional (this is what ? means) minus or plus sign[0-9]+ - one or more digits (the plus means "one or more" and [0-9] is another way to say \d)$ - end of stringNote: having the sign considered part of the number is ok only if you need to parse just the number. For more general parsers handling expressions it's better to leave the sign out of the number: source streams like 3-2 could otherwise end up being parsed as a sequence of two integers instead of an integer, an operator and another integer. My experience is that negative numbers are better handled by constant folding of the unary negation operator at an higher level.
\d means any decimal digit, so if you are using Python 3 it will match more than just 0..9. e.g. re.match("\d", "\u0665") will match (and also int("\u0665") gives 5).
+ sign (not so common when parsing but indeed somewhat common when formatting). I've also added a note on why it's however a bad idea to consider the sign part of the number when parsing if you're aiming at a more complex parsers able to handle expressions.You need to anchor the regex at the start and end of the string:
^[0-9]+$
Explanation:
^ # Start of string
[0-9]+ # one or more digits 0-9
$ # End of string
I prefer ^[-+]?([1-9]\d*|0)$ because ^[-+]?[0-9]+$ allows the string starting with 0.
RE_INT = re.compile(r'^[-+]?([1-9]\d*|0)$')
class TestRE(unittest.TestCase):
def test_int(self):
self.assertFalse(RE_INT.match('+'))
self.assertFalse(RE_INT.match('-'))
self.assertTrue(RE_INT.match('1'))
self.assertTrue(RE_INT.match('+1'))
self.assertTrue(RE_INT.match('-1'))
self.assertTrue(RE_INT.match('0'))
self.assertTrue(RE_INT.match('+0'))
self.assertTrue(RE_INT.match('-0'))
self.assertTrue(RE_INT.match('11'))
self.assertFalse(RE_INT.match('00'))
self.assertFalse(RE_INT.match('01'))
self.assertTrue(RE_INT.match('+11'))
self.assertFalse(RE_INT.match('+00'))
self.assertFalse(RE_INT.match('+01'))
self.assertTrue(RE_INT.match('-11'))
self.assertFalse(RE_INT.match('-00'))
self.assertFalse(RE_INT.match('-01'))
self.assertTrue(RE_INT.match('1234567890'))
self.assertTrue(RE_INT.match('+1234567890'))
self.assertTrue(RE_INT.match('-1234567890'))
You are apparently using Django.
You are probably better off just using models.IntegerField() instead of models.TextField(). Not only will it do the check for you, but it will give you the error message translated in several langs, and it will cast the value from it's type in the database to the type in your Python code transparently.
import re
num="12.345678"
y = re.findall('\.[0-9.]+',num)
print(y)
Answer= ['.345678']
After that, you can convert string to float.
An old question.
Usually [+-]?[0-9]+ is sufficient, meaning on can have a plus or minus, then one must have at least one character zero to nine, then you may have more characters zero through nine.
Except when its not. Are these numbers?
\d. Oddly, int("4٥6") == 456^[+-]?[0-9]+$Once your regex is over about ten characters, switch to using an online system to create and check it. I recommend Regex101 but there are a million of them.
