import math
import numbers

def longitude(value):
    if not isinstance(value, numbers.Number):
        return value
    if value > 180 or value < -180:
        return value
    if value > 0:
        side = 'E'
    elif value < 0:
        side = 'W'
    else:
        side = ''
    return get_degree(value, side)

def latitude(value):
    if not isinstance(value, numbers.Number):
        return value
    if value > 90 or value < -90:
        return value
    if value > 0:
        side = 'N'
    elif value < 0:
        side = 'S'
    else:
        side = ''
    return get_degree(value, side)

def get_degree(value, side):
    result = u'{d}\u00b0 {m}\' {s}" {side}'
    abs_value = math.fabs(value)
    degrees = math.trunc(abs_value)
    minutes = math.trunc((abs_value * 60) % 60)
    seconds = round((abs_value * 3600) % 60, 4)
    if seconds >= 60:
        seconds = 0
        minutes += 1
    minutes = str(minutes).zfill(2)
    seconds = str(seconds).zfill(2)
    return result.format(side=side, d=degrees, m=minutes, s=seconds)
print(longitude(-108.502049))  #108° 30' 07" W
print(latitude(45.758718))  #45° 45' 31" N

反向运算

import re

def dms2dd(degrees, minutes, seconds, direction):
    dd = float(degrees) + float(minutes)/60 + float(seconds)/(60*60);
    if direction == 'S' or direction == 'W':
        dd *= -1
    return dd;

def dd2dms(deg):
    d = int(deg)
    md = abs(deg - d) * 60
    m = int(md)
    sd = (md - m) * 60
    return [d, m, sd]

def parse_dms(dms):
    parts = re.split('[^\d\w]+', dms)
    lat = dms2dd(parts[0], parts[1], parts[2], parts[3])
    lng = dms2dd(parts[4], parts[5], parts[6], parts[7])

    return (round(lat,4), round(lng,4))

dd = parse_dms("45° 45' 31\" N 108° 30' 07\" W")

print(dd)
print(dd2dms(dd[0]))