Python Fundamentals: Python Dictionaries Cheatsheet | Codecademy (2024)

Values in a Python dictionary can be accessed by placing the key within square brackets next to the dictionary. Values can be written by placing key within square brackets next to the dictionary and using the assignment operator (=). If the key already exists, the old value will be overwritten. Attempting to access a value with a key that does not exist will cause a KeyError.

To illustrate this review card, the second line of the example code block shows the way to access the value using the key "song". The third line of the code block overwrites the value that corresponds to the key "song".

my_dictionary = {"song": "Estranged", "artist": "Guns N' Roses"}
print(my_dictionary["song"])
my_dictionary["song"] = "Paradise City"

roaster = {"q1": "Ashley", "q2": "Dolly"}

Given two dictionaries that need to be combined, Python makes this easy with the .update() function.

For dict1.update(dict2), the key-value pairs of dict2 will be written into the dict1 dictionary.

For keys in both dict1 and dict2, the value in dict1 will be overwritten by the corresponding value in dict2.

dict1 = {'color': 'blue', 'shape': 'circle'}
dict2 = {'color': 'red', 'number': 42}
dict1.update(dict2)
# dict1 is now {'color': 'red', 'shape': 'circle', 'number': 42}

Python allows the values in a dictionary to be any type – string, integer, a list, another dictionary, boolean, etc. However, keys must always be an immutable data type, such as strings, numbers, or tuples.

In the example code block, you can see that the keys are strings or numbers (int or float). The values, on the other hand, are many varied data types.

dictionary = {
 1: 'hello', 
 'two': True, 
 '3': [1, 2, 3], 
 'Four': {'fun': 'addition'}, 
See Also
Check Whether a Given Key Already Exists in a Dictionary in Python
 5.0: 5.5
}

my_dictionary = {1: "L.A. Lakers", 2: "Houston Rockets"}

When trying to look at the information in a Python dictionary, there are multiple methods that return objects that contain the dictionary keys and values.

• .keys() returns the keys through a dict_keys object.
• .values() returns the values through a dict_values object.
• .items() returns both the keys and values through a dict_items object.

ex_dict = {"a": "anteater", "b": "bumblebee", "c": "cheetah"}
ex_dict.keys()
# dict_keys(["a","b","c"])
ex_dict.values()
# dict_values(["anteater", "bumblebee", "cheetah"])
ex_dict.items()
# dict_items([("a","anteater"),("b","bumblebee"),("c","cheetah")])

# without default
{"name": "Victor"}.get("name")
# returns "Victor"
{"name": "Victor"}.get("nickname")
# returns None
# with default
{"name": "Victor"}.get("nickname", "nickname is not a key")
# returns "nickname is not a key"

famous_museums = {'Washington': 'Smithsonian Institution', 'Paris': 'Le Louvre', 'Athens': 'The Acropolis Museum'}
famous_museums.pop('Athens')
print(famous_museums) # {'Washington': 'Smithsonian Institution', 'Paris': 'Le Louvre'}