4 Best Ways to Check If Number is in Python List

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💡 Problem Formulation: In Python, we often need to determine if a number is present in a list. This list could include integers, floats, or a mix of various data types.

The goal is to find a clear and efficient way to check for the presence of a specific number in this list without writing extensive amounts of code.

Method 1: Using the in Operator

The most straightforward way to check if a number is in a list in Python is by using the in operator. This built-in operator is designed for membership testing and returns True if the specified number is found in the list, and False otherwise.

my_list = [1, 2, 3, 4, 5]
number_to_check = 3

is_present = number_to_check in my_list
print(is_present)  
# Output: True

In the code, number_to_check is evaluated against my_list using the in operator. The expression evaluates to True if number_to_check exists in my_list, and the result is stored in the is_present variable.

Method 2: Using the any() Function

Another Pythonic way to check for the presence of a number in a list is using the any() function. This function takes an iterable and returns True if any of the elements is True. Combined with a generator expression, it can be used to test if a number is in a list.

my_list = [1, 2, 3, 4, 5]
number_to_check = 6

is_present = any(number_to_check == num for num in my_list)
print(is_present)  
# Output: False

Here, the any() function iterates over a generator expression that checks if number_to_check equals any number in my_list. If a match is found, any() returns True immediately.

Method 3: Using a Loop

For more complex conditions or additional checking, a loop can be used to iterate through each element and check for the presence of the number. This method offers more control and the ability to add further logic inside the loop.

my_list = [1, 2, 3, 4, 5]
number_to_check = 3
is_present = False

for num in my_list:
    if num == number_to_check:
        is_present = True
        break

print(is_present)  # Output: True

The loop method checks each item in my_list against number_to_check. If a match is found, is_present is set to True and the loop is exited using break to avoid unnecessary iterations.

👉 The Most Pythonic Way to Check If a List Contains an Element

Method 4: Using the count() Method

Lists in Python have a built-in method called count(), which returns the number of occurrences of a value in the list. Checking if the count is greater than zero can determine if the number is in the list.

my_list = [1, 2, 3, 4, 5]
number_to_check = 4

is_present = my_list.count(number_to_check) > 0
print(is_present) 
# Output: True

The count() method is invoked on my_list with number_to_check as its argument. If number_to_check is present at least once, the method returns a count greater than zero, thereby setting is_present to True.

Summary/Discussion

Checking if a number is in a list in Python can be accomplished through several straightforward methods.

  • Method 1: Using the in operator is the simplest and most readable way.
  • Method 2: The any() function is a more Pythonic solution, especially useful when used with generator expressions.
  • Method 3: A loop provides more control and the opportunity to include additional logic during iteration.
  • Method 4: Lastly, the count() method is best when you also want to know the number of occurrences in the list.

💡 Recommended: Python Membership “in” Operator