Python Dictionaries
Dictionaries are a very important Python data structure.
While lists allow you to create collections of values, dictionaries allow you to create collections of key / value pairs.
Here is a dictionary example with one key/value pair:
dog = { 'name': 'Roger' }
The key can be any immutable value like a string, a number or a tuple. The value can be anything you want.
A dictionary can contain multiple key/value pairs:
dog = { 'name': 'Roger', 'age': 8 }
You can access individual key values using this notation:
dog['name'] # 'Roger'
dog['age'] # 8
Using the same notation you can change the value stored at a specific index:
dog['name'] = 'Syd'
And another way is using the get()
method, which has an option to add a default value:
dog.get('name') # 'Roger'
dog.get('test', 'default') # 'default'
The pop()
method retrieves the value of a key, and subsequently deletes the item from the dictionary:
dog.pop('name') # 'Roger'
The popitem()
method retrieves and removes the last key/value pair inserted into the dictionary:
dog.popitem()
You can check if a key is contained into a dictionary with the in
operator:
'name' in dog # True
Get a list with the keys in a dictionary using the keys()
method, passing its result to the list()
constructor:
list(dog.keys()) # ['name', 'age']
Get the values using the values()
method, and the key/value pairs tuples using the items()
method:
print(list(dog.values()))
# ['Roger', 8]
print(list(dog.items()))
# [('name', 'Roger'), ('age', 8)]
Get a dictionary length using the len()
global function, the same we used to get the length of a string or the items in a list:
len(dog) #2
You can add a new key/value pair to the dictionary in this way:
dog['favorite food'] = 'Meat'
You can remove a key/value pair from a dictionary using the del
statement:
del dog['favorite food']
To copy a dictionary, use the copy() method:
dogCopy = dog.copy()
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