Human: index of a number in a list. Assistant: 
Here is a Python function to index a number in a list

import re

def _index_of_number(number, list):
    """
    Return the index of the number in the list.
    """
    for i in range(len(list)):
        if list[i] == number:
            return i
    return -1

# Enter the number
number = 10

# Enter the list
list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]

# Calling the function
index = _index_of_number(number, list)

print(index)

#Example Output
# 9

#Remember to inspect code for bugs.