unittest.mock: asserting partial match for method argument

import mock

class AnyStringWith(str):
    def __eq__(self, other):
        return self in other

...
result = database.Query('complicated sql with an id: %s' % id)
database.Query.assert_called_once_with(AnyStringWith(id))
...

Preemptively requires a matching string

def arg_should_contain(x):
    def wrapper(arg):
        assert str(x) in arg, "'%s' does not contain '%s'" % (arg, x)
    return wrapper

...
database.Query = arg_should_contain(id)
result = database.Query('complicated sql with an id: %s' % id)

UPDATE

Using libraries like callee, you don't need to implement AnyStringWith.

from callee import Contains

database.Query.assert_called_once_with(Contains(id))

https://callee.readthedocs.io/en/latest/reference/operators.html#callee.operators.Contains

You can just use unittest.mock.ANY :)

from unittest.mock import Mock, ANY

def foo(some_string):
    print(some_string)

foo = Mock()
foo("bla")
foo.assert_called_with(ANY)

As described here - https://docs.python.org/3/library/unittest.mock.html#any