Python Itertools.dropwhile() Function with Examples

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Itertools Module:

Itertools is a Python module that contains a collection of functions for dealing with iterators. They make it very simple to iterate through iterables such as lists and strings.

Itertools.dropwhile() Function:

Only after the func. in argument returns false for the first time does Python’s dropwhile() function return an iterator.

Syntax:

dropwhile(function, sequence)

Examples:

Example1:

Input:

Given List = [6, 7, -3, -1, 4]

Output:

[-3, -1, 4]

Explanation:

Here it removes the positive numbers 6, 7 and the condition becomes false 
when the number the number is -3. so, the list remains unchanged afterwards.

Example2:

Input:

Given List = [3, 6, 8, -4, -9, 10, 56]

Output:

[-4, -9, 10, 56]

Itertools.dropwhile() Function with Examples in Python

Method #1: Using Built-in Functions (Static Input)

Approach:

  • Import itertools module using the import keyword.
  • Create a function say checkpositive which accepts the number as argument and returns True if the number is greater than 0.
  • Inside the function, return True if the given argument is greater than 0.
  • Give the list as static input and store it in a variable.
  • Pass the above function and given list as the arguments to the itertools.dropwhile()  function and store it in a variable.
  • Convert the above result into a list using the list() function and store it in another variable.
  • Print the above result.
  • The Exit of the Program.

Below is the implementation:

# Import itertools module using the import keyword.
import itertools

# Create a function say checkpositive which accepts the number as argument and
# returns True if the number is greater than 0.


def checkpositive(num):
    # Return True if the given argument is greater than 0
    return num > 0


# Give the list as static input and store it in a variable.
gvn_lst = [6, 7, -3, -1, 4]
# Pass the above function and given list as the arguments to the
# itertools.dropwhile()  function and store it in a variable.
rslt = itertools.dropwhile(checkpositive, gvn_lst)
# Convert the above result into a list using the list() function and store it
# in another variable.
rslt_lst = list(rslt)
# Print the above result.
print(rslt_lst)

Output:

[-3, -1, 4]

Method #2: Using Built-in Functions (User Input)

Approach:

  • Import itertools module using the import keyword.
  • Create a function say checkpositive which accepts the number as argument and returns True if the number is greater than 0.
  • Inside the function, return True if the given argument is greater than 0.
  • Give the list as user input using list(),map(),input(),and split() functions.
  • Store it in a variable.
  • Pass the above function and given list as the arguments to the itertools.dropwhile()  function and store it in a variable.
  • Convert the above result into a list using the list() function and store it in another variable.
  • Print the above result.
  • The Exit of the Program.

Below is the implementation:

# Import itertools module using the import keyword.
import itertools

# Create a function say checkpositive which accepts the number as argument and
# returns True if the number is greater than 0.


def checkpositive(num):
    # Return True if the given argument is greater than 0
    return num > 0


# Give the list as user input using list(),map(),input(),and split() functions.
# Store it in a variable.
gvn_lst = list(map(int, input(
   'Enter some random List Elements separated by spaces = ').split()))
# Pass the above function and given list as the arguments to the
# itertools.dropwhile()  function and store it in a variable.
rslt = itertools.dropwhile(checkpositive, gvn_lst)
# Convert the above result into a list using the list() function and store it
# in another variable.
rslt_lst = list(rslt)
# Print the above result.
print(rslt_lst)

Output:

Enter some random List Elements separated by spaces = 3 6 8 -4 -9 10 56
[-4, -9, 10, 56]