Python Program to Find Factorial of Number Using Recursion

Question

The factorial of a number is the product of all the integers from 1 to that number.

For example, the factorial of 6 is 12345*6 = 720. Factorial is not defined for negative numbers and the factorial of zero is one, 0! = 1.

def recur_factorial(n):
   if n == 1:
       return n
   else:
       return n*recur_factorial(n-1)

num = 7

# check if the number is negative
if num < 0:
   print("Sorry, factorial does not exist for negative numbers")
elif num == 0:
   print("The factorial of 0 is 1")
else:
   print("The factorial of", num, "is", recur_factorial(num))

Here's two lines of code to help you get started `command = input("enter command: ").split()` and `print command` — user3386109, Oct 20 '21 at 06:01
In the input example `IA B` references a vertex that is not added yet with `IV` -- it comes only at the third input. Your current code would produce an error because of that. Please explain the desired behaviour for such a case. — trincot, Oct 20 '21 at 07:21
Does this answer your question? [Are there a way to use while loop function as a list tracker? and mix with FileI/O?](https://stackoverflow.com/questions/64168905/are-there-a-way-to-use-while-loop-function-as-a-list-tracker-and-mix-with-filei) It's basically asking the same thing as you, except maintaining a todo-list instead of maintaining a graph. — Stef, Oct 20 '21 at 11:08

score 3 · Accepted Answer · answered Oct 20 '21 at 07:28

I would like help just to know how to read the entries and call the functions

For that purpose you can add the following code below your functions:

# main program
method = {
    "IV": add_node,
    "IA": add_edge,
    "RV": delete_node,
    "RA": delete_edge
}
numinputlines = int(input())
for _ in range(numinputlines):
    instruction, *rest = input().split()
    if len(rest) == 3:  # There is a cost:
        rest[-1] = int(rest[-1])
    method[instruction](*rest)

The method dictionary helps to translate a 2-letter code to a method that needs to be called. As the arguments to those methods are all in the same order, you can just capture those in a list rest, and "unpack" that list when passing the arguments. There is just one special thing to take care of. Two methods get a cost argument, and it must be of number type. Since input is read as string, you need to convert that cost string to a number. The if statement takes care of this case.

This should answer your question, but it does not finish the exercise. You will still have to debug your code. For instance, currently your code will raise an exception on the example input you have given -- vertex "B" is referenced in IA B A 1 before it is added with IV B.

Also, you'll need to add the code to produce the output.

But since your question was about capturing the input and calling the functions, I have left the rest for you to tackle.

How could I implement the output, since you touched on this subject, rs?? — João P, Oct 20 '21 at 14:26
That would be a different question. You would have to count the vertices and edges that your code collected in the `graph` object. If you cannot make it work, then ask a new question, providing your attempt and where it went wrong. — trincot, Oct 20 '21 at 14:32

Muhteva · Answer 2 · 2021-10-30T12:03:07.810

How do I calculate a factorial of an integer in Python? Note that the factorial function is defined only for positive integers; therefore, you should also check that n >= 0 and that isinstance(n, int). Otherwise, raise a ValueError or a TypeError respectively.

def factorial(n): 
    if(not isinstance(n, int) or n < 0):
       raise ValueError("Invalid argument")

    if (n==1 or n==0):          
        return 1      
    else:          
        return (n * factorial(n - 1)) 
  
# Driver Code 
num = int(input("Please enter a number"))
print("Factorial : ",factorial(num))

Python Program to Find Factorial of Number Using Recursion

2 Answers2