how to use probability in python program

I am new in python. my question how to take probability in python. I have a data set like this

Class A there is marks 40 10 10 20 10 How can i take probability from these marks like 10 is 3 times from total 5. 3/5 ?

#!/usr/bin/env python3
"""reducer.py"""
import sys

# Create a dictionary to map marks
Marksprob = {}

# Get input from stdin
for line in sys.stdin:
    #Remove spaces from beginning and end of the line
    line = line.strip()

    # parse the input from mapper.py
    ClassA, Marks = line.split('\t', 1)


# Create function that returns probability percent rounded to one decimal place
def event_probability(event_outcomes, sample_space):
    probability = (event_outcomes / sample_space) * 100
    return round(probability, 1)


# Sample Space
ClassA = 25

# Determine the probability of drawing a heart
Marks = 12
grade_probability = event_probability(Marks, ClassA)

# Print each probability
print(str(grade_probability) + '%')