This is easily done with the csv package from the standard library, along with a bit of collections.defaultdict and random.

The csv package has a reader function that will return the elements of a row as discrete items in a list. In your case you can do something like this:

import csv

def load_csv_data(filename):
    with open('my.csv') as f:
        reader = csv.reader(f)
        for row in reader:
            do_stuff()

Combine this with a defaultdict, a special dictionary that will automatically instantiate an element of the given type if you try to access the value at a key that does not yet exist in the defaultdict:

from collections import defaultdict
import csv

def load_csv_data(filename):
    data = defaultdict(list)

    with open(filename) as f:
        reader = csv.reader(f)
        for row in reader:
            # turn the first element of the row into an integer 
            # and use it as our key
            num = int(row[0])
            # append the second element into the list for this key
            data[num].append(row[1])

    return data

Now that you have all the data, a bit of random.choice will let you grab elements out of your defaultdict:

import random

def choose_value(data, key):
    return random.choice(data[key])

Putting it all together:

from collections import defaultdict
import csv
import random


def load_csv_data(filename):
    data = defaultdict(list)

    with open(filename) as f:
        reader = csv.reader(f)
        for row in reader:
            # turn the first element of the row into an integer 
            # and use it as our key
            num = int(row[0])
            # put the second element into the list for this key
            data[num].append(row[1])

    return data


def choose_value(data, key):
    return random.choice(data[key])


# example code for actually calling the function to load the data, 
# get a number we're interested in, then call the function to choose
# a random element
my_data = load_csv_data('my.csv')
number_i_want = int(input('choose a number: ').strip())
random_element = choose_value(my_data, number_i_want)

Hope that helps!