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

Last update on March 29 2025 13:03:36 (UTC/GMT +8 hours)

6. Drop Until Positive

Write a Python program to make an iterator that drops elements from the iterable as soon as an element is a positive number.

Sample Solution:

Python Code:

import itertools as it
def drop_while(nums):
    return it.dropwhile(lambda x : x < 0, nums)
nums = [-1,-2,-3,4,-10,2,0,5,12]
print("Original list: ",nums)
result = drop_while(nums)
print("Drops elements from the iterable when a positive number arises \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("Drops elements from the iterable when a positive number arises \n",list(result))

Sample Output:

Original list:  [-1, -2, -3, 4, -10, 2, 0, 5, 12]
Drops elements from the iterable when a positive number arises 
 [4, -10, 2, 0, 5, 12]
Original list:  [-1, -2, -3, 4, -10, 2, 0, 5, 12]
Drops elements from the iterable when a positive number arises 
 [4, -10, 2, 0, 5, 12]

For more Practice: Solve these Related Problems:

• Write a Python program to create an iterator that drops elements from an iterable until the first positive number is encountered, then yields the rest.
• Write a Python program to build an iterator that skips all elements until a condition (element > 0) is met, then applies a transformation to the remaining items.
• Write a Python program to create an iterator that drops elements until a positive number appears and then stops if a negative appears later.
• Write a Python program to construct an iterator that ignores elements until the first positive number, then collects elements into groups of two using itertools.

Python Code Editor:

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