Python - Check if list contain particular digits

When you need to check if all numbers in a list are composed only of specific digits, you can use string operations and set comparison. This is useful for validating numbers that should only contain certain digits.

Example

Below is a demonstration of checking if list elements contain only particular digits ?

numbers = [415, 133, 145, 451, 154]

print("The list is:")
print(numbers)

allowed_digits = [1, 4, 5, 3]

# Convert allowed digits to string set for faster lookup
digit_string = ''.join([str(digit) for digit in allowed_digits])
all_numbers = ''.join([str(num) for num in numbers])

result = True
for char in all_numbers:
    if char not in digit_string:
        result = False
        break

if result:
    print("All elements are made from required digits")
else:
    print("Some elements contain other digits")

The list is:
[415, 133, 145, 451, 154]
All elements are made from required digits

Using Set Operations

A more efficient approach using set operations ?

numbers = [415, 133, 145, 999]
allowed_digits = {1, 4, 5, 3}

print("Numbers:", numbers)
print("Allowed digits:", allowed_digits)

# Check each number individually
for num in numbers:
    num_digits = set(int(digit) for digit in str(num))
    if num_digits.issubset(allowed_digits):
        print(f"{num}: Contains only allowed digits")
    else:
        print(f"{num}: Contains forbidden digits {num_digits - allowed_digits}")

Numbers: [415, 133, 145, 999]
Allowed digits: {1, 3, 4, 5}
415: Contains only allowed digits
133: Contains only allowed digits
145: Contains only allowed digits
999: Contains forbidden digits {9}

Function Approach

Creating a reusable function to check digit constraints ?

def check_digits_only(numbers, allowed_digits):
    """Check if all numbers contain only specified digits"""
    allowed_set = set(str(d) for d in allowed_digits)
    
    for num in numbers:
        num_digits = set(str(num))
        if not num_digits.issubset(allowed_set):
            return False, num
    return True, None

# Test the function
test_numbers = [415, 133, 145, 451, 154]
allowed = [1, 4, 5, 3]

is_valid, invalid_num = check_digits_only(test_numbers, allowed)

if is_valid:
    print("? All numbers contain only allowed digits")
else:
    print(f"? Number {invalid_num} contains forbidden digits")

? All numbers contain only allowed digits

Comparison of Methods

Conclusion

Use set operations for efficient digit validation. The function approach provides reusability and better error reporting for identifying which numbers contain forbidden digits.