22 – Set operations with dict.keys()

Dictionaries have a method keys that returns a view over the keys of the dictionary. These objects support set operations, which means you can manipulate dictionary keys very efficiently and conveniently.

For example, for two dictionaries dict1 and dict2, you can easily compute:

1. the keys available simultaneously in both dictionaries with dict1.keys() & dict2.keys();

2. the keys available in dict1 but not in dict2 with dict1.keys() - dict2.keys(); and

3. the keys available in either dictionary with dict1.keys() | dict2.keys().

Here are the corresponding examples:

en_pt = {  # dict1
    "yellow": "amarelo",
    "red": "vermelho",
}

en_fr = {  # dict2
    "red": "rouge",
    "blue": "bleu",
}

# Keys in both:
print(en_pt.keys() & en_fr.keys())
# {'red'}

# Keys in en_pt but not in en_fr:
print(en_pt.keys() - en_fr.keys())
# {'yellow'}

# Keys in either:
print(en_pt.keys() | en_fr.keys())
# {'red', 'yellow', 'blue'}