The base64 Module

The base64 encoding scheme is used to convert arbitrary binary data to plain text. To do this, the encoder stores each group of three binary bytes as a group of four characters from the following set:

ABCDEFGHIJKLMNOPQRSTUVWXYZ abcdefghijklmnopqrstuvwxyz 0123456789+/

In addition, the = character is used for padding at the end of the data stream.

Example 4-18 shows how the encode and decode functions work on file objects.

Example 4-18. Using the base64 Module to Encode Files

File: base64-example-1.py import base64 MESSAGE = "life of brian" file = open("out.txt", "w") file.write(MESSAGE) file.close() base64.encode(open("out.txt"), open("out.b64", "w")) base64.decode(open("out.b64"), open("out.txt", "w")) print "original:", repr(MESSAGE) print "encoded message:", repr(open("out.b64").read()) print "decoded message:", repr(open("out.txt").read()) original: 'life of brian' encoded message: 'bGlmZSBvZiBicmlhbg==12' decoded message: 'life of brian'

Example 4-19 shows the encodestring and decodestring functions converting between strings. The functions are currently implemented as wrappers on top of encode and decode, using StringIO objects for input and output.

Example 4-19. Using the base64 Module to Encode Strings

File: base64-example-2.py import base64 MESSAGE = "life of brian" data = base64.encodestring(MESSAGE) original_data = base64.decodestring(data) print "original:", repr(MESSAGE) print "encoded data:", repr(data) print "decoded data:", repr(original_data) original: 'life of brian' encoded data: 'bGlmZSBvZiBicmlhbg==12' decoded data: 'life of brian'

Example 4-20 shows how to convert a username and a password to an HTTP basic authentication string. (Note that you don't really have to work for the NSA to be able to decode this format.)

Example 4-20. Using the base64 Module for Basic Authentication

File: base64-example-3.py import base64 def getbasic(user, password): # basic authentication (according to HTTP) return base64.encodestring(user + ":" + password) print getbasic("Aladdin", "open sesame") 'QWxhZGRpbjpvcGVuIHNlc2FtZQ=='

Finally, Example 4-21 shows a small utility that converts a GIF image to a Python script, for use with the Tkinter library.

Example 4-21. Using the base64 Module to Wrap GIF Images for Tkinter

File: base64-example-4.py import base64, sys if not sys.argv[1:]: print "Usage: gif2tk.py giffile >pyfile" sys.exit(1) data = open(sys.argv[1], "rb").read() if data[:4] != "GIF8": print sys.argv[1], "is not a GIF file" sys.exit(1) print '# generated from', sys.argv[1], 'by gif2tk.py' print print 'from Tkinter import PhotoImage' print print 'image = PhotoImage(data="""' print base64.encodestring(data), print '""")' # generated from samples/sample.gif by gif2tk.py from Tkinter import PhotoImage image = PhotoImage(data=""" R0lGODlhoAB4APcAAAAAAIAAAACAAICAAAAAgIAAgACAgICAgAQEBIwEBIyMBJRUlISE/LRUBAQE ... AjmQBFmQBnmQCJmQCrmQDNmQDvmQEBmREnkRAQEAOw== """)