Python : How to write a function in python

#!/usr/bin/python
import re
def getBM (eng):
    a = re.compile('No rain')
    tiada_hujan = a.match(eng)
    b = re.compile('rain')
    hujan = b.match(eng)
    c = re.compile('fair')
    cerah = c.match(eng)
    d = re.compile('Weather Fair')
    cerah2 = d.match(eng)
    p1 = re.compile('Weather Fair')
    p2 = re.compile('Clear')
    p3 = re.compile('Hazy')
    p4 = re.compile('Windy')
    p5 = re.compile('No rain')
    p6 = re.compile('Cloudy')
    p7 = re.compile('Cloudy over coastal areas')
    p8 = re.compile('Cloudy over inland areas')
    p9 = re.compile('Rain')
    p10 = re.compile('Intermittent rain occasionally moderate')
    p11 = re.compile('Intermittent rain occasionally heavy')
    p12 = re.compile('Widespread intermittent rain')
    p13 = re.compile('Isolated rain')
    p14 = re.compile('Isolated rain over coastal areas')
    p15 = re.compile('Isolated rain over inland areas')
    p16 = re.compile('Scattered rain')
    p17 = re.compile('Scattered rain over coastal areas')
    p18 = re.compile('Scattered rain over inland areas')
    p19 = re.compile('Showers')
    p20 = re.compile('Isolated showers')
    p21 = re.compile('Isolated showers over coastal areas')
    p22 = re.compile('Isolated showers over inland areas')
    p23 = re.compile('Thunderstorms')
    p24 = re.compile('Isolated thunderstorms')
    p25 = re.compile('Scattered thunderstorms')
    p26 = re.compile('Widespread thunderstorms') 
    mp1 = p1.match(eng)
    mp2 = p2.match(eng)
    mp3 = p3.match(eng)
    mp4 = p4.match(eng)
    mp5 = p5.match(eng)
    mp6 = p6.match(eng)
    mp7 = p7.match(eng)
    mp8 = p8.match(eng)
    mp9 = p9.match(eng)
    mp10 = p10.match(eng)
    mp11 = p11.match(eng)
    mp12 = p12.match(eng)
    mp13 = p13.match(eng)
    mp14 = p14.match(eng)
    mp15 = p15.match(eng)
    mp16 = p16.match(eng)
    mp17 = p17.match(eng)
    mp18 = p18.match(eng)
    mp19 = p19.match(eng)
    mp20 = p20.match(eng)
    mp21 = p21.match(eng)
    mp22 = p22.match(eng)
    mp23 = p23.match(eng)
    mp24 = p24.match(eng)
    mp25 = p25.match(eng)
    mp26 = p26.match(eng)
 
    if tiada_hujan:
        return "Tiada Hujan"
    if hujan:
        return "Hujan"
    if cerah:
        return "Cerah" 
    if cerah2:
        return "Cerah"
    if mp1:
        return "Cuaca Baik"
    if mp2:
        return "Cerah"
    if mp3:
        return "Berjerebu"
    if mp4:
        return "Berangin"
    if mp5:
        return "Tiada Hujan"
    if mp6:
        return "Mendung"
    if mp7:
        return "Mendung di kawasan pantai"
    if mp8:
        return "Mendung di kawasan pedalaman"
    if mp9:
        return "Hujan"
    if mp10:
        return "Hujan sekejap-sekejap kadangkala sederhana"
    if mp11:
        return "Hujan sekejap-sekejap kadangkala lebat"
    if mp12:
        return "Hujan sekejap-sekejap yang menyeluruh"
    if mp13:
        return "Hujan di satu dua tempat"
    if mp14:
        return "Hujan di beberapa tempat di kawasan pantai"
    if mp15:
        return "Hujan di beberapa tempat di kawasan pedalaman"
    if mp16:
        return "Hujan curah/sementara di satu dua tempat"
    if mp17:
        return "Hujan curah/sementara di kawasan pantai"
    if mp18:
        return "Hujan curah/sementara di kawasan pedalaman"
    if mp19:
        return "Hujan curah"
    if mp20:
        return "Hujan curah di satu dua tempat"
    if mp21:
        return "Hujan curah di kawasan pantai"
    if mp22:
        return "Hujan curah di kawasan pedalaman"
    if mp23:
        return "Ribut petir"
    if mp24:
        return "Ribut petir di satu dua tempat"
    if mp25:
        return "Ribut petir di beberapa tempat"
    if mp26:
        return "Ribut petir di kebanyakan tempat"
    else:
        return eng
 
# example usage : 
print "translating 'No rain' = " + getBM("No rain")