Best way to handle a keyerror in a dict

collections.defaultdict could help to build a pythonic code:

count = collections.defaultdict(int) # => default value is 0
...
count[event] += 1 # will end to 1 on first hit and will increment later

The most appropriate data structure for what you want to do is collections.Counter, where missing keys have an implicit value of 0:

from collections import Counter
events = Counter()
for e in "foo", "bar", "foo", "tar":
    events[e] += 1

You can use dict.get if you want to use dict

mydict[key] = mydict.get(key, 0) + 1

Or you can handle KeyError

try:
    mydict[key] += 1
except KeyError:
    mydict[key] = 1

Or you can use defaultdict

from collections import defaultdict
mydict = defaultdict(int)
mydict[key] += 1

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