Python lottery balls probability: name is not defined-CodePudding

Please excuse my beginners' mistakes :) I have a task that asks me to find probabilities for user input amounts of total lottery balls and balls drawn. There's most likely something else wrong with my code as well, but I can't get past the error code that says n is not defined. This is what I have:

import math

def winning(n, p):
    """Find the probability of guessing all balls correct"""
    a = math.factorial(n)/(math.factorial(n - p) * math.factorial(p))
    b = 1/a
    return b
win = winning(n, p)

def main():
    n = int(input("Enter the total number of lottery balls:", ))
    # number of balls
    p = int(input("Enter the number of the drawn balls:", ))
    # number of balls drawn
    if p > n:
        print("At most the total number of balls can be drawn.")
    if n < 1:
        print("The number of balls must be a positive number.")
    else:
        print("The probability of guessing all", p, "balls correctly is", win)

main()

Also, is math.factorial() a working way to use factorials in Python or should I use something else?

CodePudding user response：

You are making a call to winning(n, p) without n or p having been defined beforehand. As Tim mentions, moving your call to winning(n, p) to after your main() definition would mean it is called AFTER n and p are declared by the user.

For example the following produces your error:

def sum(a, b):
  return (a   b)

sum(a, b)

a = int(input('Enter 1st number: '))
b = int(input('Enter 2nd number: '))

whereas the following does not:

def sum(a, b):
  return (a   b)

a = int(input('Enter 1st number: '))
b = int(input('Enter 2nd number: '))

sum(a, b)

CodePudding user response：

How about utilizing math.comb to calculate the binomial coefficient instead of calculating it manually:

"""Lottery Probability Calculator."""

import math
import numpy as np


def get_lottery_coverage(total_balls: int, balls_drawn: int) -> int:
  return math.comb(total_balls, balls_drawn)


def get_int_input(prompt: str) -> int:
  while True:
    try:
      return int(input(prompt))
    except ValueError:
      print('Error: Enter a integer, try again...')


def main() -> None:
  print('Lottery Probability Calculator')
  print('==============================')
  total_balls = get_int_input('Enter the total number of lottery balls: ')
  if total_balls < 1:
    print('Error: The number of lottery balls must be a positive number.')
  balls_drawn = get_int_input('Enter the number of balls drawn: ')
  if balls_drawn < 1:
    print('Error: The number of balls drawn must be a positive number.')
  if balls_drawn > total_balls:
    print(f'Error: At most {total_balls} can be drawn.')
  print(f'The probability of guessing all {balls_drawn} balls correctly is:')
  total_coverage = get_lottery_coverage(total_balls, balls_drawn)
  win_probability = 1 / total_coverage
  win_probability_percentage = win_probability * 100
  print(f'{np.format_float_positional(win_probability, trim="-")}')
  print('or')
  print(f'{np.format_float_positional(win_probability_percentage, trim="-")}%')
  print('or')
  print(f'1 in {total_coverage:,}')


if __name__ == '__main__':
  main()

Example Usage:

Lottery Probability Calculator
==============================
Enter the total number of lottery balls: 49
Enter the number of balls drawn: 6
The probability of guessing all 6 balls correctly is:
0.00000007151123842018516
or
0.000007151123842018516%
or
1 in 13,983,816