Python: Make an iterator that drops elements from the iterable as soon as a condition is true

Last update on March 29 2025 13:02:55 (UTC/GMT +8 hours)

7. Drop While Negative

Write a Python program to make an iterator that drops elements from the iterable as long as the elements are negative; afterwards, it returns every element.

Sample Solution:

Python Code:

import itertools as it
def drop_while(nums):
    return it.takewhile(lambda x : x < 0, nums)
nums = [-1,-2,-3,4,-10,2,0,5,12]
print("Original list: ",nums)
result = drop_while(nums)
print("Drop elements from the said list as long as the elements are negative\n",list(result))
#Alternate solution
def negative_num(x):
    return x < 0
def drop_while(nums):
    return it.dropwhile(negative_num, nums)
nums = [-1,-2,-3,4,-10,2,0,5,12]
print("Original list: ",nums)
result = drop_while(nums)
print("Drop elements from the said list as long as the elements are negative\n",list(result))

Sample Output:

Original list:  [-1, -2, -3, 4, -10, 2, 0, 5, 12]
Drop elements from the said list as long as the elements are negative
 [-1, -2, -3]
Original list:  [-1, -2, -3, 4, -10, 2, 0, 5, 12]
Drop elements from the said list as long as the elements are negative
 [4, -10, 2, 0, 5, 12]

For more Practice: Solve these Related Problems:

• Write a Python program to make an iterator that drops elements from an iterable while they are negative and then returns the remaining elements unchanged.
• Write a Python program to create an iterator that skips over initial negative numbers and then groups the remaining numbers in pairs.
• Write a Python program to build an iterator that discards elements while they are negative and then applies a cumulative sum to the rest.
• Write a Python program to drop elements from an iterable as long as they are negative, and once a non-negative is found, yield both that and the following element.

Python Code Editor:

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