[python] Python regex for integer?

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?

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.

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 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