in
tests for the existence of a key in a dict
:
d = {"key1": 10, "key2": 23}
if "key1" in d:
print("this will execute")
if "nonexistent key" in d:
print("this will not")
Use dict.get()
to provide a default value when the key does not exist:
d = {}
for i in range(10):
d[i] = d.get(i, 0) + 1
To provide a default value for every key, either use dict.setdefault()
on each assignment:
d = {}
for i in range(10):
d[i] = d.setdefault(i, 0) + 1
or use defaultdict
from the collections
module:
from collections import defaultdict
d = defaultdict(int)
for i in range(10):
d[i] += 1