Python Check if Key Exists in Dictionary

1. Introduction

Working with dictionaries is a fundamental part of programming in Python. Dictionaries are collections of key-value pairs. A common operation when working with dictionaries is checking whether a specific key exists within the dictionary.

Definition

In Python, a 'key' in a dictionary is a unique identifier used to store and retrieve a value within the dictionary. Checking for a key's existence is performed to ensure that accessing the key's associated value will not cause an error.

2. Program Steps

1. Initialize a dictionary with some key-value pairs.

2. Decide the key you want to check for existence.

3. Use a conditional statement or a membership test to determine if the key exists.

4. Print the result stating whether the key exists or not.

3. Code Program

# Initialize a dictionary
my_dict = {'name': 'John', 'age': 30, 'city': 'New York'}

# The key to check
key_to_check = 'age'

# Check if the key exists in the dictionary
if key_to_check in my_dict:
    print(f"The key '{key_to_check}' exists in the dictionary.")
else:
    print(f"The key '{key_to_check}' does not exist in the dictionary.")

Output:

The key 'age' exists in the dictionary.

Explanation:

1. my_dict is a dictionary containing three key-value pairs.

2. key_to_check is set to the string 'age', which is the key we are looking to find in my_dict.

3. The if statement uses the in keyword to test for the presence of key_to_check within the dictionary's keys.

4. The print function outputs the result, which uses an f-string to dynamically insert the key_to_check into the message.

5. The output confirms that the key 'age' is indeed present in my_dict.