Python Dictionaries¶
A Python dictionary is a collection of key-value pairs. Each key is connected to a value, and you can use the key to access the value associated with it. Dictionaries are mutable, which means you can modify them after they are created. They are also unordered, meaning they do not maintain any order of the elements stored in them.
Creating a Dictionary¶
To create a dictionary, use curly braces {} with pairs of keys and values separated by colons :.
Here's an example:
my_dict = {"name": "John", "age": 30, "city": "New York"}
print(my_dict)
{'name': 'John', 'age': 30, 'city': 'New York'}
Checking the length of a dictionary¶
print(len(my_dict))
2
Accessing Values¶
You can access the value associated with a specific key using square brackets []:
name = my_dict["name"]
print(name) # Output: John
age = my_dict.get("age")
print(age)
John 31
Adding and Modifying Items¶
Adding or modifying items in a dictionary is straightforward. Assign a value to a key directly:
# Adding a new key-value pair
my_dict["email"] = "john@example.com"
# Modifying an existing key-value pair
my_dict["age"] = 31
print(my_dict)
{'name': 'John', 'age': 31, 'city': 'New York', 'email': 'john@example.com'}
Removing Items¶
You can remove items using the del statement or the pop() method:
# Remove the key 'city' using del
del my_dict["city"]
# Remove the key 'email' using pop
email = my_dict.pop("email")
print(my_dict)
{'name': 'John', 'age': 31}
Looping Through a Dictionary¶
You can loop through a dictionary using a for loop:
for key, value in my_dict.items():
print(f"{key}: {value}")
name: John age: 31
Checking if Key Exists¶
To check if a key exists in a dictionary, use the in keyword:
if "name" in my_dict:
print("Name is present in the dictionary")
Dictionary Methods¶
Dictionaries have several useful methods, such as items(), keys(), values(), and more:
# Get all items
items = my_dict.items()
print(items)
# Get all keys
keys = my_dict.keys()
print(keys)
# Get all values
values = my_dict.values()
print(values)
dict_items([('name', 'John'), ('age', 31)])
dict_keys(['name', 'age'])
dict_values(['John', 31])
Nested Dictionaries¶
You can store dictionaries within dictionaries, which is known as nested dictionaries:
family = {
"John": {"age": 30, "city": "New York"},
"Jane": {"age": 28, "city": "Boston"}
}
print(family)
{'John': {'age': 30, 'city': 'New York'}, 'Jane': {'age': 28, 'city': 'Boston'}}
Return a new sorted list of keys in the dictionary¶
dict_one = {0:'sunday', 2: 'tuesday', 3: 'wednesday', 4: 'thursday', 1: 'monday'}
print(sorted(dict_one))
[0, 1, 2, 3, 4]
Dictionary Comprehension¶
squared = {x: x*x for x in range(10)}
print(squared)
{0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25, 6: 36, 7: 49, 8: 64, 9: 81}
Updates the dictionary with the elements from another dictionary object or from any other key/value pairs¶
dict1 ={0:"zero",4:"four",5:"five"}
dict2={2:"two"}
# updates the value of key 2
dict1.update(dict2)
print(dict1)
{0: 'zero', 4: 'four', 5: 'five', 2: 'two'}