Question

Is there a python library for encoding ascii data to 7-bit GSM character set (for sending SMS)?

Answer 1

There is now 🙂

Thanks to Chad for pointing out that this wasn’t quite right

Python2 version

# -*- coding: utf8 -*- 
gsm = (u"@£$¥èéùìòÇ\nØø\rÅåΔ_ΦΓΛΩΠΨΣΘΞ\x1bÆæßÉ !\"#¤%&'()*+,-./0123456789:;<=>"
       u"?¡ABCDEFGHIJKLMNOPQRSTUVWXYZÄÖÑܧ¿abcdefghijklmnopqrstuvwxyzäöñüà")
ext = (u"````````````````````^```````````````````{}`````\\````````````[~]`"
       u"|````````````````````````````````````€``````````````````````````")

def gsm_encode(plaintext):
    res = ""
    for c in plaintext:
        idx = gsm.find(c)
        if idx != -1:
            res += chr(idx)
            continue
        idx = ext.find(c)
        if idx != -1:
            res += chr(27) + chr(idx)
    return res.encode('hex')

print gsm_encode(u"Hello World")

The output is hex. Obviously you can skip that if you want the binary stream

Python3 version

# -*- coding: utf8 -*- 
import binascii
gsm = ("@£$¥èéùìòÇ\nØø\rÅåΔ_ΦΓΛΩΠΨΣΘΞ\x1bÆæßÉ !\"#¤%&'()*+,-./0123456789:;<=>?"
       "¡ABCDEFGHIJKLMNOPQRSTUVWXYZÄÖÑܧ¿abcdefghijklmnopqrstuvwxyzäöñüà")
ext = ("````````````````````^```````````````````{}`````\\````````````[~]`"
       "|````````````````````````````````````€``````````````````````````")

def gsm_encode(plaintext):
    res = ""
    for c in plaintext:
        idx = gsm.find(c);
        if idx != -1:
            res += chr(idx)
            continue
        idx = ext.find(c)
        if idx != -1:
            res += chr(27) + chr(idx)
    return binascii.b2a_hex(res.encode('utf-8'))

print(gsm_encode("Hello World"))