Short Python 3 In-Memory Database Test

#!/usr/bin/env python import sys from collections import defaultdict class Table(object): def __init__(self, name, column_names, data): self.name = name self.column_names = column_names self.data = data def select(self, projected_column_names): return Table("Select", None, None) def where(self, column_name, value): return Table("Where", None, None) def __repr__(self): return ", ".join(self.column_names) + "\n" + \ "\n".join([", ".join([str(val) for val in row]) for row in self.data]) class DB(object): def __init__(self): self.table_map = {} def add_table(self, table): self.table_map[table.name] = table def table(self, table_name): return self.table_map[table_name] def right_join(self, left_table, left_table_key_name, right_table, right_table_key_name): return Table("RightJoin", None, None) def left_join(self, left_table, left_table_key_name, right_table, right_table_key_name): return Table("LeftJoin", None, None) def outer_join(self, left_table, left_table_key_name, right_table, right_table_key_name): return Table("OuterJoin", None, None) def inner_join(self, left_table, left_table_key_name, right_table, right_table_key_name): return Table("InnerJoin", None, None) def main(): department_table = Table('departments', ['id', 'name'], [ [0, 'engineering'], [1, 'finance']]) user_table = Table('users', ['id', 'department_id', 'name'], [ [0, 0, 'Ian'], [1, 0, 'John'], [2, 1, 'Eddie'], [3, 1, 'Mark']]) salary_table = Table('salaries', ['id', 'user_id', 'amount'], [ [0, 0, 100], [1, 1, 150], [2, 1, 200], [3, 3, 200], [4, 3, 300], [5, 4, 400]]) db = DB() db.add_table(user_table) db.add_table(department_table) db.add_table(salary_table) # should print something like # id, department_id, name # 1, 0, John print(db.table('users') \ .where('id', 1) \ .select(['id', 'department_id', 'name'])) # should print something like # users.name, departments.name # Ian, engineering # John, engineering print(db.inner_join(db.table('users'), 'department_id', db.table('departments'), 'id') \ .where('departments.name', 'engineering') \ .select(['users.name', 'departments.name'])) # should print something like # users.name, salaries.amount # Ian, 100 # John, 150 # John, 200 # Mark, 200 # Mark, 300 # Eddie, None print(db.left_join(db.table('users'), 'id', db.table('salaries'), 'user_id') \ .select(['users.name', 'salaries.amount'])) # should print something like # users.name, salaries.amount # Ian, 100 # John, 150 # John, 200 # Mark, 200 # Mark, 300 # None, 400 print(db.right_join(db.table('users'), 'id', db.table('salaries'), 'user_id') \ .select(['users.name', 'salaries.amount'])) # should print something like # users.name, salaries.amount # Ian, 100 # John, 150 # John, 200 # Mark, 200 # Mark, 300 # Eddie, None # None, 400 print(db.outer_join(db.table('users'), 'id', db.table('salaries'), 'user_id') \ .select(['users.name', 'salaries.amount'])) main()