Challenge: 11.1.2018 - First Factorial

FirstFactorial.py

#!/usr/local/bin/python3

#   ---------------------------------- MODULE IMPORTS ---------------------------------------- #
import sys, cProfile
from functools import reduce

#   --------------------------------- CHALLENGE CONTEXT -------------------------------------- #
#	Using the Python language, have the function FirstFactorial(num) take the num parameter being 
#	passed and return the factorial of it (e.g. if num = 4, return (4 * 3 * 2 * 1)). For the test 
#	cases, the range will be between 1 and 18 and the input will always be an integer. 
#
#	Sample Test Cases
#	Input:4
#	Output:24
#
#	Input:8
#	Output:40320
#
#   --------------------------------- PROCESS WIREFRAME -------------------------------------- #
#
#	1. Need to ensure the input value is an integer
#	2. Create list of all numbers from input num to 1
#	3. Need to multiply each number against the other
#	4. Return the computed value
#
#   --------------------------------- ENVIRONMENT SETUP -------------------------------------- #

class InvalidInputException ( Exception ) :
	""" Custom exception class which extends BaseException used to throw properly named exception
	upon encountering invalid input data.
	"""
	
	pass

#   --------------------------------- PROPOSED SOLUTION -------------------------------------- #

class FirstFactorial :
	""" Class designed to return the product of a Factorial mathmatics operation.  This class does
	not return an instance when instantiated, rather the product of the mathmatics operation."""
	
	def __new__ ( cls, num, profile ) :
		""" Used in place of __init__ to make the class uninstantiable and return a value rather
		than an instance.
		
		:param: num (int) / integer to use to calculate factorial product
		:param: profile (bool) / used to determine if profiler should be executed for input number
		:throws: InvalidInputException (exception) / Custom exception class to handle Input errors
		:return (int): / product of factorial calculation
		"""
	
		#	1. Ensure input number is an integer by attempting to cast value to int
		#		1a. To accomplish, we attempt to cast the input value to int() type and catch the TypeError/ValueError 
		#			if the conversion cannot happen because the value type is incorrect
		#	2. Create a list of all numbers from n to 1 to then be multiplied against each other 
		#		using list comprehension and range loop in reverse order from highest number to smallest.
		#	3. Use reduce to walk the list of integers and multiply each against the next.
		#		3a. Here, reduce will call the registered lambda function for each element in the list.
		#			Reduce will execute lambda for the first 2 elements in the list, then the product is
		#			multiplied by the next element in the list, and so-on, until the list ends.
		
		try :
			if profile :
				cProfile.run( 'FirstFactorial( %s )' % num )
		
			num = int( num )
			return reduce( lambda x, y: x * y, [n for n in range(num, 0, -1)] )
			
		except ( TypeError, ValueError ) :
			raise InvalidInputException ( "Input must be an integer, greater than 0!" )
		
		
#   --------------------------------- ALTERNATE SOLUTIONS ------------------------------------ #
		
#   --------------------------------- MAIN EXECUTION BLOCK ----------------------------------- #
if __name__ == '__main__' :

	# Only run the profiler if the command line switch is passed with the call of the script
	# E.g.: python FirstFactorial.py -p
	profile = True if len( sys.argv ) > 1 and sys.argv[1] == '-p' else False

	# keep this function call here, where "input()" is user input
	print( FirstFactorial( input(), profile ) )