Python – Extract Key's Value, if Key Present in List and Dictionary

Sometimes we need to extract a value from a dictionary only if the key exists in both a list and the dictionary. Python provides the all() function combined with the in operator to check multiple conditions efficiently.

Basic Example

Here's how to extract a key's value when the key is present in both a list and dictionary ?

my_list = ["Python", "is", "fun", "to", "learn", "and", "teach", "cool", "object", "oriented"]

my_dictionary = {"Python": 2, "fun": 4, "learn": 6}

K = "Python"
print("The key is:", K)
print("The list is:", my_list)
print("The dictionary is:", my_dictionary)

my_result = None
if all(K in container for container in [my_dictionary, my_list]):
    my_result = my_dictionary[K]

print("The result is:", my_result)

The key is: Python
The list is: ['Python', 'is', 'fun', 'to', 'learn', 'and', 'teach', 'cool', 'object', 'oriented']
The dictionary is: {'Python': 2, 'fun': 4, 'learn': 6}
The result is: 2

How It Works

The all() function returns True only if all elements in the iterable are True. In this case:

• K in my_dictionary checks if the key exists in the dictionary

• K in my_list checks if the key exists in the list

• all() ensures both conditions are met before extracting the value

Testing with Different Keys

Let's test with keys that exist in different combinations ?

my_list = ["Python", "is", "fun", "to", "learn"]
my_dictionary = {"Python": 2, "fun": 4, "learn": 6, "code": 8}

def extract_value(key, dictionary, items_list):
    if all(key in container for container in [dictionary, items_list]):
        return dictionary[key]
    return None

# Test different keys
test_keys = ["Python", "fun", "code", "missing"]

for key in test_keys:
    result = extract_value(key, my_dictionary, my_list)
    print(f"Key '{key}': {result}")

Key 'Python': 2
Key 'fun': 4
Key 'code': None
Key 'missing': None

Alternative Approaches

You can also use explicit conditions for better readability ?

my_list = ["Python", "is", "fun", "to", "learn"]
my_dictionary = {"Python": 2, "fun": 4, "learn": 6}

key = "fun"

# Method 1: Using all()
result1 = my_dictionary[key] if all(key in container for container in [my_dictionary, my_list]) else None

# Method 2: Explicit conditions
result2 = my_dictionary[key] if key in my_dictionary and key in my_list else None

print("Method 1 result:", result1)
print("Method 2 result:", result2)

Method 1 result: 4
Method 2 result: 4

Conclusion

Use all() with generator expressions to check if a key exists in multiple containers simultaneously. This approach is concise and efficient for validating conditions across different data structures before extracting values.