Database lab:

Here is a transcript from an sqlite session, showing three queries:

sqlite> select * from mailing_list;
philg@mit.edu|Philip Greenspun
ogrady@fastbuck.com|Michael O'Grady

sqlite> select * from phone_numbers;
ogrady@fastbuck.com|work|(800) 555-1212
ogrady@fastbuck.com|home|(617) 495-6000
philg@mit.edu|work|(617) 253-8574

sqlite> select * from mailing_list, phone_numbers
   ...>  where mailing_list.email = phone_numbers.email;
ogrady@fastbuck.com|Michael O'Grady|ogrady@fastbuck.com|work|(800) 555-1212
ogrady@fastbuck.com|Michael O'Grady|ogrady@fastbuck.com|home|(617) 495-6000
philg@mit.edu|Philip Greenspun|philg@mit.edu|work|(617) 253-8574

Write a python program that achieves the same effect without using any
database libraries.  Use an in-memory database consisting only of
built-in data Python structures (sets and tuples), and queries
consisting only of ordinary Python expressions (list comprehensions).