$ curl cheat.sh/
#  [`in`][1] is the intended way to test for the existence of a key in a
#  [`dict`][2].

 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()`][3]:

 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()`][4] repeatedly or [`defaultdict`][5]
#  from the [`collections`][6] 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.
#  
  #  [1]: https://docs.python.org/reference/expressions.htmlmembership-
#  test-operations
  #  [2]: https://docs.python.org/library/stdtypes.htmldict
  #  [3]: https://docs.python.org/library/stdtypes.htmldict.get
  #  [4]: https://docs.python.org/library/stdtypes.htmldict.setdefault
  #  [5]: https://docs.python.org/library/collections.htmlcollections.de
#  faultdict
  #  [6]: https://docs.python.org/library/collections.html
#  
#  [Chris B.] [so/q/1602934] [cc by-sa 3.0]

$
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