Check if a given key already exists in a dictionary

Question

I wanted to test if a key exists in a dictionary before updating the value for the key. I wrote the following code:

if 'key1' in dict.keys():   print "blah" else:   print "boo" 

I think this is not the best way to accomplish this task. Is there a better way to test for a key in the dictionary?

Answer 1

in is the intended way to test 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") 

If you wanted a default, you can always use dict.get():

d = dict()  for i in range(100):     key = i % 10     d[key] = d.get(key, 0) + 1 

and if you wanted to always ensure a default value for any key you can either use dict.setdefault() repeatedly or defaultdict from the collections module, like so:

from collections import defaultdict  d = defaultdict(int)  for i in range(100):     d[i % 10] += 1 

but in general, the in keyword is the best way to do it.