How does collections.defaultdict work?

Question

I\'ve read the examples in python docs, but still can\'t figure out what this method means. Can somebody help? Here are two examples from the python docs

>         


        

Answer 1

Without defaultdict, you can probably assign new values to unseen keys but you cannot modify it. For example:

import collections
d = collections.defaultdict(int)
for i in range(10):
  d[i] += i
print(d)
# Output: defaultdict(, {0: 0, 1: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8, 9: 9})

import collections
d = {}
for i in range(10):
  d[i] += i
print(d)
# Output: Traceback (most recent call last): File "python", line 4, in  KeyError: 0