How to do inputs in Python

Question

I have to open file in Python, what looks like this:

Rapla;Tartu;157
Tallinn;Narva;211
Valga;Haapsalu;249
Viljandi;Paide;71
Tartu;Rakvere;123
Rapla;Narva;259
Paide;Narva;196
Paide;Tallinn;92

I want to get program to work like this with an example:

Please enter starting point: Rapla
Now please enter ending point: Tartu
Distance between Rapla and Tartu is 157 km.

I managed to make a list in python, but I'm fairly new in Python and I dont know, how to do inputs, so I could get a accetable output.

What I managed to do so far:

town1 = []
town2 = []
distance = []

f = open('town.csv')
for list in f:
    x = list.split(';')
    town1.append(x[0])
    town2.append(x[1])
    distance.append(x[2])

f.close()

n = len(town1)
for i in range(n):
    print('Starting point is: ' + town1[i])
    print('Ending point is:  ' + town2[i])
    print('Distance between', town1[i], 'and', town2[i], 'is', distance[i], 'km.')

Program just prints every single town starting point and ending point with distance, but I want to make program to ask me starting point and ending point.

Answer 1

# assumes Python 2.x
from collections import defaultdict
import csv

def load_distances(fname):
    distance = defaultdict(dict)
    with open(fname, "rb") as inf:
        incsv = csv.reader(inf, delimiter=";")
        for town_a, town_b, dist in incsv:
            distance[town_a][town_b] = int(dist)
    return distance

def main():
    distance = load_distances("town.csv")

    town_a = raw_input("Please enter starting point: ")
    town_b = raw_input("Now please enter ending point: ")
    if town_a not in distance or town_b not in distance[town_a]:
        print("I don't know how to get from {} to {}".format(town_a, town_b))
    else:
        print("Distance between {} and {} is {} km.".format(town_a, town_b, distance[town_a][town_b]))

if __name__=="__main__":
    main()

If you are using Python 3, you need to replace raw_input() with input() and open(fname, "rb") with open(fname, newline="") .

defaultdict is a special type of dict ; if you ask it for an object it doesn't have, it returns a new default object instead of causing an error.

Answer 2

To read user input, use the input() function. Based on the parentheses around your print() calls, I'm guessing taht you are using Python 3. Beware that input() in Python 2 works differently; input() in Python 3 is roughly equivalent to raw_input() in Python 2.

To read the data file, use the csv module with delimiter=';' .

Answer 3

Here is a way to do it for python 2.x using filters.

#!/usr/bin/env python
# -*- coding: utf-8 -*-

def loadTowns():
    with open('town.csv') as f:
        return [row.split(';') for row in f.read().splitlines()]

towns = loadData()

start = raw_input("Enter your start: ")
towns = filter(lambda r: r[0] == start, towns)

dest = raw_input("Enter your destination: ")
towns = filter(lambda r: r[1] == dest, towns)

print towns[0][2] if towns else "Not a valid selection"