Python check if none in list

Check if Any Element in List is None in Python

This tutorial will discuss about a unique way to check if any element in list is none in Python.

To check if a List contains any None value, we can iterate over all the list elements, and for each element we can check if it is None or not.

We can do that using the any() method. In this method, we will iterate over all elements of list, using a for loop and evaluate if any element is None or not. It will result in a boolean sequence of True and False values. A True value denotes that corresponding value is None in the List.

The any() method will return True, if any element from the list satisfies the condition i.e. if any element is None in the List.

Let’s see the complete example,

Frequently Asked:

listObj = [1, None, "Magic", True, 12, 89.0] # Check if List contains any None Value if any(elem is None for elem in listObj): print("Yes, List contains at least a None value") else: print("No, List does not have any None value")

Yes, List contains at least a None value

Summary

We learned a way to check if List contains any None value in Python.

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Check if all elements in a list are None in Python

In this article we will discuss different ways to check if a list contains only None or not.

sample_list = [None, None, None, None]

Now we want to confirm that all items in this list are None. There are different ways to do that. Let’s discuss them one by one,

Check if a list contains only None using for loop

The first solution that comes to our mind is using for loop.
Logic is, Iterate over all the items of a list using for loop and for each item check if it is None or not. As soon as a non None item is found, break the loop because it means all items of list are not None. Whereas, if the loop ends and not even a single non None item is found, then it proves that all items of the list are None.

Frequently Asked:

Let’s create a function that accepts a list and check if all items are none or not using the above logic,

def check_if_all_none(list_of_elem): """ Check if all elements in list are None """ result = True for elem in list_of_elem: if elem is not None: return False return result

Use this function to check if all items in list are None,

sample_list = [None, None, None, None] # Check if list contains only None result = check_if_all_none(sample_list) if result: print('Yes List contains all None') else: print('Not all items in list are None')

Yes List contains all None

Generic function to check if all items in list matches a given item like None

In the above example, we created a separate function just to check if all items in a list are None or not, although it does the work but it is not a reusable function. So, let’s create a generic function to check if all items of a list are same and also matches the given element,

def check_if_all_same(list_of_elem, item): """ Check if all elements in list are same and matches the given item""" result = True for elem in list_of_elem: if elem != item: return False return result

This function accepts a list and an item as an argument. Then checks if all items in the given list matches the given item using the same logic as previous example. We can use this function to check if all items of list are None,

sample_list = [None, None, None, None] # Check if all items in list are same and are None result = check_if_all_same(sample_list, None) if result: print('Yes List contains all None') else: print('Not all items in list are None')

Yes List contains all None

Now we can use this function at other places too like, to confirm if all elements in a list matches the given number or string etc.

Check if a list contains only None using List comprehension

Let’s look at a pythonic way to confirm if all items in a list are None,

def check_if_all_same_2(list_of_elem, item): """ Using List comprehension, check if all elements in list are same and matches the given item""" return all([elem == item for elem in list_of_elem])

Let’s use this function to check all items of list are None,

sample_list = [None, None, None, None] # Check if all items in list are same and are None result = check_if_all_same_2(sample_list, None) if result: print('Yes List contains all None') else: print('Not all items in list are None')

Yes List contains all None

It is a one line solution.
Using list comprehension we created a Boolean list from the existing list. Each element in this bool list corresponds to an item for the main list. Basically, in the List Comprehension we iterated over the given list and for each element we checked if it is None or not. If it is None then added True in the bool list else added False. Now using all() checked if the bool list contains only True or not. If all() function returns True, then it means our main list contains only None.

We can use this function in a generic way too. For example check if all items in the list matches a given string,

sample_list = ['is', 'is', 'is', 'is', 'is'] # Check if all items in list are string 'is' result = check_if_all_same_2(sample_list, 'is') if result: print('Yes List contains same elements') else: print('Not all items in list are same')

Yes List contains same elements

The complete example is as follows,

def check_if_all_none(list_of_elem): """ Check if all elements in list are None """ result = True for elem in list_of_elem: if elem is not None: return False return result def check_if_all_same(list_of_elem, item): """ Check if all elements in list are same and matches the given item""" result = True for elem in list_of_elem: if elem != item: return False return result def check_if_all_same_2(list_of_elem, item): """ Using List comprehension, check if all elements in list are same and matches the given item""" return all([elem == item for elem in list_of_elem]) def main(): print('*** Check if a list contains only None using for loop ***') sample_list = [None, None, None, None] # Check if list contains only None result = check_if_all_none(sample_list) if result: print('Yes List contains all None') else: print('Not all items in list are None') print('*** Check if a list contains only None using Generic function ***') sample_list = [None, None, None, None] # Check if all items in list are same and are None result = check_if_all_same(sample_list, None) if result: print('Yes List contains all None') else: print('Not all items in list are None') print('*** Check if a list contains only None using List comprehension ***') sample_list = [None, None, None, None] # Check if all items in list are same and are None result = check_if_all_same_2(sample_list, None) if result: print('Yes List contains all None') else: print('Not all items in list are None') print('*** check if all items in the list matches a given string ***') sample_list = ['is', 'is', 'is', 'is', 'is'] # Check if all items in list are string 'is' result = check_if_all_same_2(sample_list, 'is') if result: print('Yes List contains same elements') else: print('Not all items in list are same') if __name__ == '__main__': main()

*** Check if a list contains only None using for loop *** Yes List contains all None *** Check if a list contains only None using Generic function *** Yes List contains all None *** Check if a list contains only None using List comprehension *** Yes List contains all None *** check if all items in the list matches a given string *** Yes List contains same elements

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How To Check If Any Item In A List Is None Using Python

To check if any item in a list is None in python, we can use the membership Operators or list comprehension.

Check if any item in a list is None using Python

In Python, ‘None’ is a specific object indicating that the object is missing the presence of a value. The Python Null object is the singleton None.

Note: constant ‘None’ is defined as False, so when combined using the same logical operator or always returns False.

To check if any item in a list is None, we have the following ways:

Use the membership Operators

The membership operators in Python include ‘in’ and ‘not in’.

The ‘in’ operator will return True if the specified argument occurs in a set and vice versa.

The ‘not in’ operator will return True if the specified argument is not in the set and vice versa.

• Initializes a list of both strings and None.
• Use the membership operator to check if the value None appears in the list.

# A list consisting of strings and None myList = ["Learn", None, "Share", None, None, "IT"] # Use the in operator to check if any item in a list is None if None in myList: print('The list contains the value None') else: print('The list does not contain the value None')

The list contains the value None

Or you can use the ‘not in’ operator to check.

# A list consisting of strings and None myList = ["Learn", None, "Share", None, None, "IT"] # Use the in operator to check if any item in a list is None if None not in myList: print('The list does not contain the value None') else: print('The list contains the value None')

The list contains the value None

The program still outputs that command line because there is a None value in the list.

Use list comprehension

• Initializes a list of both strings and None.
• Use the list comprehension to output the None values ​​contained in the list.

# A list consisting of strings and None myList = ["Learn", None, "Share", None, None, "IT"] # Use list comprehension to output None values in the list result = [x for x in myList if x is None] print('The value None appears in the list:', result)

The value None appears in the list: [None, None, None]

Use the any() function

• True if at least one element in an iterable is True.
• False if all elements in iterable are False or iterable is empty.

• Initialize a list of both strings and None.
• Use the any() function to check if the value None appears in the list.

# A list consisting of strings and None myList = ["Learn", None, "Share", None, None, "IT"] # Use the any() function to output None values in the list result = any(x is None for x in myList) print('The value None appears in the list:', result)

The value None appears in the list: True

Summary

Above are some ways I often use to check if any item in a list is None using Python. After reading this article, you may have better ways for this topic.

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My name is Jason Wilson, you can call me Jason. My major is information technology, and I am proficient in C++, Python, and Java. I hope my writings are useful to you while you study programming languages.

Name of the university: HHAU
Major: IT
Programming Languages: C++, Python, Java

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