Negate a boolean or a List of Booleans in Python

# Table of Contents

1. Negate a boolean in Python
2. Flip the boolean values in a List in Python
3. Negate the boolean values in a NumPy array

# Negate a boolean in Python

Use the not operator to negate a boolean, e.g. result = not my_bool.

The not operator will negate the boolean value, returning True if the value is False and False if the value is True.

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my_bool = True

result = not my_bool
print(result)  # 👉️ False

We used the not operator to negate a boolean value.

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print(not True)  # 👉️ False

print(not False)  # 👉️ True

The not operator returns True if the value is falsy and False if the value is truthy.

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print(not True)  # 👉️ False
print(not False)  # 👉️ True
print(not 'bobbyhadz.com')  # 👉️ False
print(not '')  # 👉️ True

All values that are not truthy are considered falsy. The falsy values in Python are:

• constants defined to be falsy: None and False.
• 0 (zero) of any numeric type.
• empty sequences and collections: "" (empty string), () (empty tuple), [] (empty list), {} (empty dictionary), set() (empty set), range(0) (empty range).

# Negate a boolean using operator.not_

You can also use the operator.not_ method to negate a boolean.

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import operator

print(operator.not_(True))  # 👉️ False

print(operator.not_(False))  # 👉️ True

The operator.not_ method negates the given object and returns the result.

The operator.not_ method is mostly used when you need to flip a list of boolean values with map().

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import operator

list_of_booleans = [True, True, False, False]

new_list = list(map(operator.not_, list_of_booleans))

print(new_list) # 👉️ [False, False, True, True]

# Don't use the bitwise NOT operator to negate booleans

Note that you shouldn't use the bitwise ~ not operator to negate boolean values.

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print(~True) # 👉️ -2
print(~False) # 👉️ -1

The bitwise ~ not operator returns unexpected results when used with boolean values because booleans are a subclass of int.

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print(isinstance(True, int)) # 👉️ True

The operator doesn't return the negated boolean value, it returns the negated integer value.

# Flip the boolean values in a list in Python

To flip the boolean values in a list:

1. Use a list comprehension to iterate over the list.
2. Use the not operator to flip each boolean value.
3. The new list will contain the negation of the boolean values in the original list.

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my_list = [True, True, False, False]

new_list = [not item for item in my_list]
print(new_list)  # 👉️ [False, False, True, True]

We used a list comprehension to flip the boolean values in a list.

On each iteration, we use the not operator to flip the current boolean value and return the result.

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my_list = [True, True, False, False]

new_list = [not item for item in my_list]
print(new_list)  # 👉️ [False, False, True, True]

The not operator returns True if the value is falsy and False if the value is truthy.

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print(not True)  # 👉️ False
print(not False)  # 👉️ True

print(not 'bobbyhadz.com')  # 👉️ False
print(not '')  # 👉️ True

All values that are not truthy are considered falsy. The falsy values in Python are:

• constants defined to be falsy: None and False.
• 0 (zero) of any numeric type.
• empty sequences and collections: "" (empty string), () (empty tuple), [] (empty list), {} (empty dictionary), set() (empty set), range(0) (empty range).

Alternatively, you can use the map() function.

# Flip the boolean values in a list using map()

This is a three-step process:

1. Pass a lambda function and the list to the map() function.
2. The map() function will call the lambda function with each boolean in the list.
3. Use the list() class to convert the map object to a list.

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my_list = [True, True, False, False]

new_list = list(map(lambda x: not x, my_list))
print(new_list)  # 👉️ [False, False, True, True]

The map() function takes a function and an iterable as arguments and calls the function with each item of the iterable.

Lastly, we used the list() class to convert the map object to a list.

The list class takes an iterable and returns a list object.

# Negate the boolean values in a NumPy array

If you need to negate the boolean values in a NumPy Array, use the numpy.logical_not() method.

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import numpy as np


arr = np.array([True, True, False, False], dtype=bool)

result = np.logical_not(arr)
print(result)  # 👉️ [False False  True  True]

Make sure you have NumPy installed to be able to run the code sample.

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pip install numpy

# 👇️ or with pip3
pip3 install numpy

We used the numpy.logical_not method to negate a NumPy array.

The logical_not method applies the not operator to the elements of the array.

The method returns a new array containing the negation of each element in the original array.

# Negate the boolean values in a NumPy array using bitwise NOT

The bitwise not ~ operator can be used to negate a NumPy array of booleans.

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import numpy as np


arr = np.array([True, True, False, False], dtype=bool)

result = ~arr

print(result)  # 👉️ [False False  True  True]

You can also use the invert method to achieve the same result.

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import numpy as np


arr = np.array([True, True, False, False], dtype=bool)

result = np.invert(arr)

print(result)  # 👉️ [False False  True  True]

The numpy.invert method computes bit-wise inversion, or bit-wise NOT, element-wise.

The method takes an array of booleans and inverts the values in the array.

There is also a bitwise_not method in NumPy.

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import numpy as np


arr = np.array([True, True, False, False], dtype=bool)

result = np.bitwise_not(arr)

print(result)  # 👉️ [False False  True  True]

The bitwise_not method is an alias for invert.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• How to print Boolean values in Python
• Using booleans in an if statement in Python
• Convert Booleans to Integers and vice versa in Python
• Generate random Boolean (True or False) values in Python
• Taking user input boolean (True/False) values in Python