string interpolation for python

[Adrian Hunt]

Hi Yingjie,

Consider this snippet of "safe" code:

| enc = bobsencryption.Encoder('Some secret key')
|
| username = raw_input('Enter your username:')
| password = raw_input('Enter your password:')
|
| print
| print username + ', please wait while we dial-up and log you in...'
|
| connection = server.dialup(00441635074745)
| connection.send('login ' + enc([username, password]))

Code like this could already be out there and safe-ish (well, if
they've included a little validation and error-checking.) Now consider
that your $formatting$ is added and the "company" upgrades Python,
resulting in the following:

| Enter your username: $enc.key$
| Enter your password: dontneedone
|
| Some secret key, please wait while we dial-up and log you in...

It could break old code... okay you may say you should’nt allow 
certain characters but if they're printable and used in a controlled
environment those characters can dramatically increase the security
of a username and password.



Adrian