Python - List Initialization with alternate 0s and 1s

In this article, we will learn how to initialize a list with alternate 0s and 1s. Given a list length, we need to create a list where elements alternate between 1 and 0 starting with 1.

Method 1: Using a For Loop

The simplest approach is to iterate through the range and append values based on whether the index is even or odd ?

# initializing an empty list
result = []
length = 7

# iterating through the range
for i in range(length):
    # checking if index is even or odd
    if i % 2 == 0:
        # appending 1 on even index
        result.append(1)
    else:
        # appending 0 on odd index
        result.append(0)

# printing the result
print(result)

The output of the above code is ?

[1, 0, 1, 0, 1, 0, 1]

Method 2: Using Slice Assignment

A more efficient approach is to pre-allocate the list and use slice assignment to fill alternate positions ?

import math

# initializing the length and list with None values
length = 7
result = [None] * length

# calculating counts for 1s and 0s
ones_count = math.ceil(length / 2)
zeros_count = length - ones_count

# assigning 1s to even indices and 0s to odd indices
result[::2] = [1] * ones_count
result[1::2] = [0] * zeros_count

# printing the result
print(result)

The output of the above code is ?

[1, 0, 1, 0, 1, 0, 1]

Method 3: Using List Comprehension

The most concise approach uses list comprehension with a conditional expression ?

length = 7

# creating list with alternating 1s and 0s using list comprehension
result = [1 if i % 2 == 0 else 0 for i in range(length)]

print(result)

The output of the above code is ?

[1, 0, 1, 0, 1, 0, 1]

Comparison

Conclusion

List comprehension provides the most concise solution for creating alternating 0s and 1s. For beginners, the for loop approach offers better readability and understanding of the logic.