Preventing KeyError in Python dictionaries • AnuRock

In my post on coding minimalism, I talked about leveraging data structures and defaults built into a language’s standard library to avoid error-prone boilerplate code.

This post is a quick reminder that Python comes with something called defaultdict that will help you avoid errors resulting from trying to access non-existent keys in a dictionary.

my_dict = dict({
    "one": 1,
    "three": 3
})

print(my_dict["two"]) # KeyError: 'two'
# To avoid KeyError, use either:
print(my_dict.get("two")) # None
# or:
print(my_dict.get("two", 0)) # 0

A more elegant solution:

from collections import defaultdict

my_dict = defaultdict(int) # default value type supplied as argument
my_dict["one"] = 1
my_dict["three"] = 3
print(my_dict["two"]) # 0