from math import radians, cos, sin, asin, sqrt

AVG_EARTH_RADIUS = 6371  # in km

def great_circle(point1, point2, miles=True):
    """ Calculate the great-circle distance bewteen two points on the Earth surface.
    :input: two 2-tuples, containing the latitude and longitude of each point
    in decimal degrees.
    Example: haversine((45.7597, 4.8422), (48.8567, 2.3508))
    :output: Returns the distance bewteen the two points.
    The default unit is kilometers. Miles can be returned
    if the ``miles`` parameter is set to True.
    """
    # unpack latitude/longitude
    lat1, lng1 = point1
    lat2, lng2 = point2

    # convert all latitudes/longitudes from decimal degrees to radians
    lat1, lng1, lat2, lng2 = list(map(radians, [lat1, lng1, lat2, lng2]))

    # calculate haversine
    lat = lat2 - lat1
    lng = lng2 - lng1
    d = sin(lat / 2) ** 2 + cos(lat1) * cos(lat2) * sin(lng / 2) ** 2
    h = 2 * AVG_EARTH_RADIUS * asin(sqrt(d))
    if miles:
        return h * 0.621371  # in miles
    else:
        return h  # in kilometers
