Python: Check whether a given key already exists in a dictionary

Last update on April 21 2025 13:00:09 (UTC/GMT +8 hours)

4. Check Key Existence in Dictionary

Write a Python program to check whether a given key already exists in a dictionary.

Sample Solution-1:

Python Code:

# Create a dictionary 'd' with key-value pairs.
d = {1: 10, 2: 20, 3: 30, 4: 40, 5: 50, 6: 60}

# Define a function 'is_key_present' that takes an argument 'x'.
def is_key_present(x):
    # Check if 'x' is a key in the dictionary 'd'.
    if x in d:
        # If 'x' is present in 'd', print a message indicating that the key is present.
        print('Key is present in the dictionary')
    else:
        # If 'x' is not present in 'd', print a message indicating that the key is not present.
        print('Key is not present in the dictionary')

# Call the 'is_key_present' function with the argument 5 to check if 5 is a key in the dictionary.
is_key_present(5)

# Call the 'is_key_present' function with the argument 9 to check if 9 is a key in the dictionary.
is_key_present(9)

Sample Output:

Key is present in the dictionary                                                                              
Key is not present in the dictionary

Flowchart:

Sample Solution-2:

Python Code:

# Define a function 'key_in_dict' that takes a dictionary 'd' and a 'key' as arguments.
# It checks if the 'key' is present in the dictionary 'd' and returns a boolean value.
def key_in_dict(d, key):
    return (key in d)

# Create a dictionary 'students' with key-value pairs.
students = {
    'Theodore': 19,
    'Roxanne': 22,
    'Mathew': 21,
    'Betty': 20
}

# Print a message indicating the start of the code section.
print("\nOriginal dictionary elements:")

# Print the original dictionary 'students'.
print(students)

# Call the 'key_in_dict' function to check if the key 'Roxanne' is present in the 'students' dictionary.
# Print the result, which is a boolean value.
print(key_in_dict(students, 'Roxanne'))

# Call the 'key_in_dict' function to check if the key 'Gina' is present in the 'students' dictionary.
# Print the result, which is a boolean value.
print(key_in_dict(students, 'Gina'))

Sample Output:

Original dictionary elements:
{'Theodore': 19, 'Roxanne': 22, 'Mathew': 21, 'Betty': 20}
True
False

Flowchart:

For more Practice: Solve these Related Problems:

Write a Python script to check if a given key exists in a dictionary using the in operator.
Write a Python script to determine key existence by iterating through the dictionary keys.
Write a Python script to use the get() method to check for a key and return a default value if it is missing.
Write a Python script to implement a function that returns True if a key exists in a dictionary and False otherwise.

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