How to add or increment a dictionary entry?

I'm currently re-engaging with Python after a long absence and loving it. However, I find myself coming across a pattern over and over. I keep thinking that there must be a better way to express what I want and that I'm probably doing it the wrong way.

The code that I'm writing is in the following form:

# foo is a dictionary
if foo.has_key(bar):
  foo[bar] += 1
else:
  foo[bar] = 1

I'm writing this a lot in my programs. My first reaction is to push it out to a helper function, but so often the python libraries supply things like this already.

Is there some simple little syntax trick that I'm missing? Or is this the way that it should be done?

Use a defaultdict:

from collections import defaultdict

foo = defaultdict(int)
foo[bar] += 1

In Python >= 2.7, you also have a separate Counter class for these purposes. For Python 2.5 and 2.6, you can use its backported version.

The dict's get() method takes an optional second parameter that can be used to provide a default value if the requested key is not found:

foo[bar] = foo.get(bar, 0) + 1