Python check if all false

Check if all elements in List are False in Python

This tutorial will discuss about unique ways to check if all elements in list are false in Python.

Table Of Contents

Technique 1: Using all() method

Using the all() method, we can confirm if a sequence contains all True values. Now, to check if a list has all False values, we can invert the values in List and check if all the values are True or not using all() method. For example, this expression will return ‘True’ if list has all False values,

all(not elem for elem in listOfElements)

Now we can use this to check if all elements in a given list are False or not.

Let’s see the complete example,

Frequently Asked:

# Example 1 listOfElements = [False, False, False, False] # check if all elements in list are False if all(not elem for elem in listOfElements): print("Yes, All elements in list are False") else: print("No, All elements in list are not False") # Example 2 listOfElements = [False, True, False, False] # check if all elements in list are False if all(not elem for elem in listOfElements): print("Yes, All elements in list are False") else: print("No, All elements in list are not False")

Yes, All elements in list are False No, All elements in list are not False

Technique 2: Using for-loop

Iterate over all the elements of List using a for loop. During iteration, for each element check if it is True or not. As soon as a True element is encountered, break the loop, and mark that list does not have all False values. We have created a function for this,

def is_all_false(listObj): '''Returns True if all elements in list are False''' result = True for elem in listObj: if elem: result = False break return result

This function accepts a list as argument, and returns True , if all the elements in this list are False . In this function, we will loop through all the values of list, and will look any non False value.

Let’s see the complete example,

def is_all_false(listObj): '''Returns True if all elements in list are False''' result = True for elem in listObj: if elem: result = False break return result # Example 1 listOfElements = [False, False, False, False] # check if all elements in list are False if is_all_false(listOfElements): print("Yes, All elements in list are False") else: print("No, All elements in list are not False") # Example 2 listOfElements = [False, True, False, False] # check if all elements in list are False if is_all_false(listOfElements): print("Yes, All elements in list are False") else: print("No, All elements in list are not False")

Yes, All elements in list are False No, All elements in list are not False

Summary

We learned about two different ways to check if a List contains all False values or not. Thanks.

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Pythonic way to check if: all elements evaluate to False -OR- all elements evaluate to True

The nice part is that one of them is guaranteed to only look at a single element. If the first element is truthy, any will immediately terminate. It it’s falsy, all will.

the itertools.tee is the touch that makes this the answer worth putting in a toolkit module. You don’t have to think about what you send it.

However if they mostly are truthy it will still go through almost all of them in the all(it1) call. if you used itertools.izip it would be more efficient (on average) for cases where there are mixed values.

@John: Only by one iteration, whose time would probably be chewed up by the object generation during zipping.

def all_bools_equal(lst): return all(lst) or not any(lst) 

Piggybacking on Ignacio Vasquez-Abram’s method, but will stop after first mismatch:

def unanimous(s): it1, it2 = itertools.tee(iter(s)) it1.next() return not any(bool(a)^bool(b) for a,b in itertools.izip(it1,it2)) 

While using not reduce(operators.xor, s) would be simpler, it does no short-circuiting.

I was curious so I ran some tests, and surprisingly this solution is 2-3× slower than mine across a bool power set with 2 to 15 elements. I didn’t think itertools.izip() would be that expensive.

I looked at yours further to really «get» what its doing. This fails mostly because so much logic is in Python, not C. I don’t think a 15-element list will give you much of a test; try testing with [1]*100000 , [0]*100000 , [1]*100000+[0] , and [0]*100000+[1] to really see the extreme differences. Also, I’d be curious how not reduce(operator.xor, s) measures up.

And even if the izip solution is much slower, it might be a better solution for cases where the input iterable is likely to be both unanimous and extremely long (perhaps produced by a generator). Here, behind the scenes, the tee only needs to store one extra element since the two tees streams are being consumed in lock step, whereas in the simpler all or not any solution, the second tee stream is not consumed until after the first is completely consumed so the whole sequence would need to be stored in memory if unanimous. Perhaps both recipes belong in the toolbox!

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Check if all values in List are False in Python

In this article, we will discuss different ways to check if all values are False in a Python List.

Table Of Contents

Using for-loop to check if all values in List are False

Iterate over all the elements of a list using a for loop, and for each element check if it is False or not. As soon as you find an element that is not False, break the loop, because it means there is at least a value in the list that does not evaluates to False . But also make sure that list is not empty. Let’s see a complete example,

listOfElements = [False, False, False, False, False, False] result = True # Check if all values are False in a List in Python for elem in listOfElements: if elem != False: result = False break if len(listOfElements) > 0 and result: print('Yes, all values are False in a List in Python') else: print('No, all values are not False in a List in Python')

Yes, all values are False in a List in Python

There were only False values in the List.

Frequently Asked:

Using all() method to check if all values in List are False

Python provides a function all(). It accepts an iterable sequence as an argument and returns True if all the elements in that sequence evaluates to True. Now, to check if all elements in a List are False or not, create a boolean list of same size. Each True value in this new boolean list represents the corresponding False Value in the original List. Then pass this new boolean list to the any() function. If it returns True, then it means the original list has only False values. But also make sure that list is not empty. Let’s see a complete example,

listOfElements = [False, False, False, False, False, False] # Check if all values are False in a List in Python if all(elem == False for elem in listOfElements) and len(listOfElements) > 0: print('Yes, all values are False in a List in Python') else: print('No, all values are not False in a List in Python')

Yes, all values are False in a List in Python

There were only False values in the List.

Using NumPy to check if all values in List are False

The NumPy module has a function all(). It accepts an array like sequence as an argument and returns True if all the elements in that sequence evaluates to True. Now, to check if List has only False values, we will create a boolean NumPy Array of same size. A value in the boolean array will be True, if the corresponding value in the original list is False. Then pass our boolean NumPy Array object to the numpy.all() function, and if it returns True, then it means our original list has only False values. Let’s see an example,

import numpy as np listOfElements = [False, False, False, False, False, False] # Create a NumPy Array from list numbers = np.array(listOfElements) # Check if all values in array are zeros if np.all(numbers == False) and len(listOfElements) > 0: print('Yes, List contains all False values') else: print('No, List does not contains all False values')

Yes, all values are False in a List in Python

There were only False values in the List.

Using Set to check if all values in List are False

In Python, a Set is a kind of data structure that contains only unique elements. So, we can convert our list to a Set and check following conditions,

• Set size should be 1.
• First element of set should be equal to first element of list and that should evaluate to False.

If both the conditions are True, then it means our list has only False values. We can verify both the conditions by comparing the set with .

Let’s see an example,

listOfElements = [False, False, False, False, False, False] # Check if all values are True in a List in Python if set(listOfElements) == : print('Yes, all values are False in a List in Python') else: print('No, all values are not False in a List in Python')

Yes, all values are False in a List in Python

There were only False values in the List.

Summary

We learned how to verify of a List has only False values in Python. Thanks.

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