Python Dictionaries

Learning Python Day 8

Python Dictionaries

In Python, dictionaries are unordered collections of key-value pairs. They are incredibly useful for storing data efficiently

Creating Dictionary

You can create a dictionary by enclosing comma-separated key-value pairs within curly braces {} or by using the dict() constructor.

# Creating a dictionary using curly braces
person = {'name': 'John', 'age': 30, 'city': 'New York'}

# Creating a dictionary using dict() constructor
person = dict(name = John, age = 30, city = New York')

Accessing Values

You can access the values in a dictionary by referring to their corresponding key using square brackets[]. If the key doesn’t exist, it will raise a KeyError. Alternatively, you can use the get() method, which returns None or a default value if the key is not found.

person = {'name': 'John', 'age': 30, 'city': 'New York'}

print(person['name'])  # Output: John
print(person.get('age'))  # Output: 30
print(person.get('gender', 'Unknown'))  # Output: Unknown

Modifying Values

You can modify the value of a specific key in a dictionary by assigning a new value to it.

person = {'name': 'John', 'age': 30, 'city': 'New York'}

person['age'] = 35
print(person)  # Output: {'name': 'John', 'age': 35, 'city': 'New York'}

Adding and Removing Key-Value Pairs

You can add new key-value pairs to a dictionary or remove existing ones using the update() method, pop() method, or the del keyword.

person = {'name': 'John', 'age': 30, 'city': 'New York'}

# Adding a new key-value pair
person['gender'] = 'Male'
print(person)  # Output: {'name': 'John', 'age': 30, 'city': 'New York', 'gender': 'Male'}

# Removing a key-value pair using del
del person['age']
print(person)  # Output: {'name': 'John', 'city': 'New York'}

# Removing a key-value pair using pop
removed_value = person.pop('city')
print(person)  # Output: {'name': 'John'}
print(removed_value)  # Output: New York

Checking Membership

You can check if a key exists in a dictionary by using the in keyword.

person = {'name': 'John', 'age': 30, 'city': 'New York'}

print('name' in person)  # Output: True
print('gender' in person)  # Output: False

Iterating Over a Dicitonary

You can iterate over the keys, values, or both using various methods like keys(), values(), and items().

person = {'name': 'John', 'age': 30, 'city': 'New York'}

# Iterating over keys
for key in person.keys():
    print(key)  # Output: name, age, city

# Iterating over values
for value in person.values():
    print(value)  # Output: John, 30, New York

# Iterating over key-value pairs
for key, value in person.items():
    print(key, value)  # Output: name John, age 30, city New York