# 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 inrange(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 inrange(10):
d[i]= d.setdefault(i,0)+1# or use defaultdict from the collections module:from collections import defaultdict
d = defaultdict(int)for i inrange(10):
d[i]+=1