Distance calculation

distance.py

import math

EARTH_RADIUS = 6378137.  # in meters


def calculate_distance(lat1, lng1, lat2, lng2):
    if not all((lat1, lng1, lat2, lng2)):
        return

    a = math.radians(lat1) - math.radians(lat2)
    b = math.radians(lng1) - math.radians(lng2)
    distance = 2 * math.asin(
            math.sqrt(
                math.pow(math.sin(a / 2), 2) + math.cos(math.radians(lat1)) *
                math.cos(math.radians(lat2)) * math.pow(math.sin(b / 2), 2))
            ) * EARTH_RADIUS
    return int(round(distance))


def pick_nearest(place_list, lat, lng):
    if not (lat and lng):
        return place_list[0]

    index = 0
    distance = float('inf')
    for i, p in enumerate(place_list):
        if p.lat and p.lng:
            cur_distance = calculate_distance(
                    p.lat, p.lng, lat, lng)
            if cur_distance < distance:
                distance = cur_distance
                index = i
    return place_list[index]