Python program to fetch the indices of true values in a Boolean list

Given a list of only boolean values, write a Python program to fetch all the indices with True values from given list.

Let’s see certain ways to do this task.

Method #1: Using itertools [Pythonic way]

itertools.compress() function checks for all the elements in list and returns the list of indices with True values.

# Python program to fetch the indices
# of true values in a Boolean list
from itertools import compress

# initializing list
bool_list = [False, True, False, True, True, True]

# printing given list
print ("Given list is : " +  str(bool_list))

# using itertools.compress()
# to return true indices.
res = list(compress(range(len(bool_list )), bool_list ))

# printing result
print ("Indices having True values are : " +  str(res))

Output:

Given list is : [False, True, False, True, True, True]
Indices having True values are : [1, 3, 4, 5]

Method #2: Using enumerate() method

enumerate() method hashes the index with its value and coupled with list comprehension can let us check for the true values.

# Python program to fetch the indices
# of true values in a Boolean list

# initializing list
bool_list = [False, True, False, True, True, True]

# printing given list
print ("Given list is : " +  str(bool_list))

# using enumerate() + list comprehension
# to return true indices.
res = [i for i, val in enumerate(bool_list) if val]


# printing result
print ("Indices having True values are : " +  str(res))

Output:

Given list is : [False, True, False, True, True, True]
Indices having True values are : [1, 3, 4, 5]

Method #3: Using filter() + range()

# Python program to fetch the indices
# of true values in a Boolean list

# initializing list
bool_list = [False, True, False, True, True, True]

# printing given list
print ("Given list is : " +  str(bool_list))

# using lambda + filter() + range()
# to return true indices.
res = list(filter(lambda i: bool_list[i], range(len(bool_list))))

# printing result
print ("Indices having True values are : " +  str(res))

Output:

Given list is : [False, True, False, True, True, True]
Indices having True values are : [1, 3, 4, 5]