Visitar URL original
Collections of key-value pairs.
my_empty_dict = {} # alternative: my_empty_dict = dict()
print(f"dict: {my_empty_dict}, type: {type(my_empty_dict)}")
dict: {}, type: <class 'dict'>
dict1 = {"value1": 1.6, "value2": 10, "name": "John Doe"}
dict2 = dict(value1=1.6, value2=10, name="John Doe")
print(dict1)
print(dict2)
print(f"equals: {dict1 == dict2}")
print(f"length: {len(dict1)}")
{'value1': 1.6, 'value2': 10, 'name': 'John Doe'}
{'value1': 1.6, 'value2': 10, 'name': 'John Doe'}
equals: True
length: 3
dict.keys(), dict.values(), dict.items()¶print(f"keys: {dict1.keys()}")
print(f"values: {dict1.values()}")
print(f"items: {dict1.items()}")
keys: dict_keys(['value1', 'value2', 'name'])
values: dict_values([1.6, 10, 'John Doe'])
items: dict_items([('value1', 1.6), ('value2', 10), ('name', 'John Doe')])
my_dict = {}
my_dict["key1"] = "value1"
my_dict["key2"] = 99
my_dict["key1"] = "new value" # overriding existing value
print(my_dict)
print(f"value of key1: {my_dict['key1']}")
{'key1': 'new value', 'key2': 99}
value of key1: new value
Accessing a nonexistent key will raise KeyError (see dict.get() for workaround):
# print(my_dict['nope'])
my_dict = {"key1": "value1", "key2": 99, "keyX": "valueX"}
del my_dict["keyX"]
print(my_dict)
# Usually better to make sure that the key exists (see also pop() and popitem())
key_to_delete = "my_key"
if key_to_delete in my_dict:
del my_dict[key_to_delete]
else:
print(f"{key_to_delete} is not in {my_dict}")
{'key1': 'value1', 'key2': 99}
my_key is not in {'key1': 'value1', 'key2': 99}
my_dict = {"ham": "good", "carrot": "semi good"}
my_other_dict = my_dict
my_other_dict["carrot"] = "super tasty"
my_other_dict["sausage"] = "best ever"
print(f"{my_dict=}\nother: {my_other_dict}")
print(f"equals: {my_dict == my_other_dict}")
my_dict={'ham': 'good', 'carrot': 'super tasty', 'sausage': 'best ever'}
other: {'ham': 'good', 'carrot': 'super tasty', 'sausage': 'best ever'}
equals: True
Create a new dict if you want to have a copy:
my_dict = {"ham": "good", "carrot": "semi good"}
my_other_dict = dict(my_dict)
my_other_dict["beer"] = "decent"
print(f"{my_dict=}\nother: {my_other_dict}")
print(f"equals: {my_dict == my_other_dict}")
my_dict={'ham': 'good', 'carrot': 'semi good'}
other: {'ham': 'good', 'carrot': 'semi good', 'beer': 'decent'}
equals: False
dict.get()¶Returns None if key is not in dict. However, you can also specify default return value which will be returned if key is not present in the dict.
my_dict = {"a": 1, "b": 2, "c": 3}
value_of_d = my_dict.get("d")
print(f"d: {value_of_d}")
value_of_d = my_dict.get("d", "my default value")
print(f"d: {value_of_d}")
d: None d: my default value
dict.pop()¶my_dict = dict(food="ham", drink="beer", sport="football")
print(f"dict before pops: {my_dict}")
food = my_dict.pop("food")
print(f"food: {food}")
print(f"dict after popping food: {my_dict}")
food_again = my_dict.pop("food", "default value for food")
print(f"food again: {food_again}")
print(f"dict after popping food again: {my_dict}")
dict before pops: {'food': 'ham', 'drink': 'beer', 'sport': 'football'}
food: ham
dict after popping food: {'drink': 'beer', 'sport': 'football'}
food again: default value for food
dict after popping food again: {'drink': 'beer', 'sport': 'football'}
dict.setdefault()¶Returns the value of key defined as first parameter. If the key is not present in the dict, adds key with default value (second parameter).
my_dict = {"a": 1, "b": 2, "c": 3}
a = my_dict.setdefault("a", "my default value")
d = my_dict.setdefault("d", "my default value")
print(f"a: {a}\nd: {d}\nmy_dict: {my_dict}")
a: 1
d: my default value
my_dict: {'a': 1, 'b': 2, 'c': 3, 'd': 'my default value'}
dict.update()¶Merge two dicts
dict1 = {"a": 1, "b": 2}
dict2 = {"c": 3}
dict1.update(dict2)
print(dict1)
# If they have same keys:
dict1.update({"c": 4})
print(dict1)
{'a': 1, 'b': 2, 'c': 3}
{'a': 1, 'b': 2, 'c': 4}
dict have to be immutable¶Thus you can not use e.g. a list or a dict as key because they are mutable types
:
# bad_dict = {['my_list'], 'value'} # Raises TypeError
Values can be mutable
good_dict = {"my key": ["Python", "is", "still", "cool"]}
print(good_dict)
{'my key': ['Python', 'is', 'still', 'cool']}