defaultdict with a parameter to the class constructor

Question

[Python 3.1]

I want defaultdict(int), except I'd like the default value to be 1 rather than 0.

1. Is there any neat way to do that?
2. Should I do that?

Answer 1

>>> def f():
        return 1
>>> a = defaultdict(f)
>>> a[1]
1

Here is an other implementation using lambda expression (from kindall):

>>> a = defaultdict(lambda: 1)

Answer 2

defaultdict(lambda: 1)

eg

>>> from collections import defaultdict
>>> a = defaultdict(lambda: 1)
>>> a["foo"] += 1
>>> a["foo"]
2

Answer 3

From the docs:

The function int() which always returns zero is just a special case of constant functions. A faster and more flexible way to create constant functions is to use itertools.repeat() which can supply any constant value (not just zero):

>>> def constant_factory(value):
...     return itertools.repeat(value).next
>>> d = defaultdict(constant_factory('<missing>'))
>>> d.update(name='John', action='ran')
>>> '%(name)s %(action)s to %(object)s' % d
'John ran to <missing>'