Python Factorial program help

Question

Here is what i wrote:

number = raw_input('Enter an integer= ')
if number < 0:
    print 'Invalid number'

else:
    for k in range(1,(number)):
        number *= k

print number

I want to be able to input any number (that is greater than 0), but when i input a number say 4 (the factorial of 4 is 24) i get this error:

Traceback (most recent call last):
  File "problem.py", line 6, in <module>
    for k in range(1,(number)):
TypeError: range() integer end argument expected, got str.

I don't understand what it means and as far as i know the code should be working, Please Help!

duffymo · Accepted Answer · 2011-06-16 23:47:08Z

4

This works perfectly: factorial.py

#!/usr/bin/env python

# imports go here

__author__ = 'Michael O. Duffy'
__status__ = "Development"

def factorial(n):
    """ Calculate a factorial of an integer """
    factorial = 1
    if n < 0:
        print 'Invalid number'
    else:
        for k in range(1,n+1):
            factorial *= k
    return factorial

if __name__ == '__main__':

    for number in range(1, 20):
        print 'n: ', number, 'n!: ', factorial(number)

You should know that this is an inefficient, academic implementation that shouldn't be used in any serious application. You'll be a lot better off using a gamma or lngamma implementation and a dictionary cache to save on calculations if you use values repeatedly:

http://mathworld.wolfram.com/GammaFunction.html

edited Jun 16, 2011 at 23:47

answered Jun 15, 2011 at 17:37

duffymo

310k46 gold badges376 silver badges570 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

SteeveDroz · Accepted Answer · 2011-06-16 08:06:49Z

2

What about recursion?

def factorial(n):
  if n < 0:
    print("ERROR!") # throw error, return -1, or whatever
  elif n <= 1:
    return 1
  else:
    return n * factorial(n - 1)

answered Jun 16, 2011 at 8:06

SteeveDroz

6,1646 gold badges36 silver badges69 bronze badges

1 Comment

Dima Thefencingdude Lukhtai Over a year ago

Thanks it works now, and im going to try out the lngamma implementation, by the way this was a part of my project for math class thanks for everybodies help!

Mark Tolonen · Accepted Answer · 2011-06-16 08:01:43Z

1

raw_input returns a string, not an integer. Create an integer this way:

number = int(raw_input('Enter an integer= '))

The user might type something besides an integer, in which case you might want to handle that possibility.

while True:
    try:
        number = int(raw_input('Enter an integer= '))
    except ValueError:
        print "That wasn't an integer"
    else:
        break

answered Jun 16, 2011 at 8:01

Mark Tolonen

181k26 gold badges182 silver badges278 bronze badges

Comments

Navakishore · Accepted Answer · 2017-07-20 08:03:48Z

-1

using xxxxx.py
num=int(raw_input("Enter a number"))
n=1
while num>=0:
  n=n*num
  num=num-1
print "Factorial of the given number is: ",n

answered Jul 20, 2017 at 8:03

Navakishore

1

Collectives™ on Stack Overflow

Python Factorial program help

4 Answers 4

Comments

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related