The best shortcut is no shortcut

#
#  main.py
#  Some Python Program
#
#  Created by Mewlan Musajan on 4/28/21.
#

triangleLength1 = 0
triangleLength2 = 0
triangleLength3 = 0

def lengthInput():
    global triangleLength1
    global triangleLength2
    global triangleLength3
    
    triangleLength1 = input('Enter first length of your triangle: ')
    triangleLength2 = input('Enter second length of your triangle: ')
    triangleLength3 = input('Enter third length of your triangle: ')

def isLengthValid():
    if triangleLength1 + triangleLength2 < triangleLength3\
     or triangleLength1 + triangleLength3 < triangleLength2\
     or triangleLength2 + triangleLength3 < triangleLength1:
        print("Valid length provided.")
    else:
        print("Invalid length provided.")

while True:
    lengthInput()
    if triangleLength1 != 0 and triangleLength2 != 0\
       and triangleLength3 != 0:
       break
    print("Length can't be nil.")

this 10 minute Python Teaching made me miserable .....