Add key_in_dict

snippets/key_in_dict.md

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+---
+title: key_in_dict
+tags: dictionary,beginner
+---
+
+Checks if the given key exists in a dictionary.
+
+- Use the `in` operator to check if `d` contains `key`.
+
+```py
+def key_in_dict(d, key):
+  return (key in d)
+```
+
+```py
+d = {'one': 1, 'three': 3, 'five': 5, 'two': 2, 'four': 4}
+key_in_dict(d, 'three') # True
+```