one 0.1.0

Not all nor any. Just the one.

Not all nor any: just the one.

one is a simple function to check if there is a unique value that evaluates to True in an iterable, and return it.

Examples:

>>> from one import one
>>> one((True, False, False))
True
>>> one((True, False, True))
False
>>> one((0, 0, 'a'))
'a'
>>> one((0, False, None))
False
>>> one((True, True))
False
>>> one(('', 1))
1

Install

pip install one

Use cases

A very frequent case is when you have values that must exclude each others.

class ShopStore(models.Model):
    address = models.CharField(max_length=200, null=True, blank=True)
    is_online = models.BooleanField(default=False)

    def clean(self):
        if not one((self.address, self.is_online)):
            raise models.ValidationError(u'A shop must be online or physical, but not both')

Attention!

send me your examples!