Distance between cities done

Author: Karan Goel

Numbers/distance.py

@@ -0,0 +1,55 @@
+#!/usr/bin/env python
+
+"""
+Distance Between Two Cities - Calculates the distance between
+two cities and allows the user to specify a unit of distance.
+This program may require finding coordinates for the cities
+like latitude and longitude.
+
+Uses the Haversine formula
+(http://www.movable-type.co.uk/scripts/latlong.html)
+
+Dependencies:
+geopy
+    pip install geopy
+"""
+
+from geopy import geocoders # to find lat/lon for the city
+import math
+
+R = 6373 # km
+
+city1 = raw_input('Enter city 1: ')
+city2 = raw_input('Enter city 2: ')
+unit = raw_input('Enter unit of distance (K = KM, M = MI): ').lower()
+
+if unit in 'km':
+
+    g = geocoders.GoogleV3()
+    
+    try:
+        city1, (lat1, lon1) = g.geocode(city1)
+        city2, (lat2, lon2) = g.geocode(city2)
+    except:
+        raise Exception('Unable to locate the citites. Check the city names.')
+    
+    # convert decimal locations to radians
+    lat1 = math.radians(lat1)
+    lon1 = math.radians(lon1)
+    lat2 = math.radians(lat2)
+    lon2 = math.radians(lon2)
+    
+    # start haversne formula
+    dlon = lon2 - lon1
+    dlat = lat2 - lat1
+    a = (math.sin(dlat/2) ** 2) + math.cos(lat1) * math.cos(lat2) * \
+    (math.sin(dlon/2) ** 2)
+    c = 2 * math.atan2(math.sqrt(a), math.sqrt(1 - a))
+    d = R * c
+    
+    if unit == 'k':
+        print 'Distance between %s and %s is %.04f km' % (city1, city2, d)
+    else:
+        print 'Distance between %s and %s is %.04f mi' % (city1, city2, d / 1.60934)
+else:
+    print 'Invalid unit input!'