quiz.py

#/usr/bin/env python3

from enum import Enum
from random import choice, randint
from datetime import datetime
from operator import add, sub, mul  # binary operations as functions!

# Enums were introduced in 3.4!
Operation = Enum('Operation', ('add', 'subtract', 'multiply'))

class Expression:
    operations = {Operation.add: ('+', add),
                  Operation.subtract: ('-', sub),
                  Operation.multiply: ('*', mul)}

    def __init__(self, operation, first_operand, second_operand):
        self.operation = operation
        self.first_operand = first_operand
        self.second_operand = second_operand

    @classmethod  # class methods!
    # the convention is to say `cls` instead of `self` for these
    def arbitrary_expression(cls, maximum_figure):
        return cls(choice(list(Operation)),
                   # gratuitously splatting a list comprehension because <3
                   *[randint(0, maximum_figure) for _ in range(2)])

    def evaluate(self):
        _symbol, action = self.operations[self.operation]
        return action(self.first_operand, self.second_operand)

    def __str__(self):  # pretty end-user string form of class
        # (contrast to __repr__, for the developer debugging string form)
        symbol, _action = self.operations[self.operation]
        return "{} {} {}".format(
            self.first_operand, symbol, self.second_operand)


def play(maximum_figure=12):
    start_time = datetime.now()
    wins = tries = 0  # multiple assignment targets!
    should_continue = True
    while should_continue:
        expression = Expression.arbitrary_expression(maximum_figure)
        try:
            user_says = input("{}\n".format(expression))
        except KeyboardInterrupt:  # catch ^C
            break

        if "done" in user_says:
            should_continue = False
        else:
            tries += 1
            try:
                user_answer = int(user_says)
                if user_answer == expression.evaluate():
                    wins += 1
                    print("Correct!")
                    continue
            except ValueError: # they typed a non-number
                pass  # fallthrough to ...
            print("Wrong. Answer was {}".format(expression.evaluate()))
    end_time = datetime.now()
    total_time = (end_time - start_time).total_seconds()
    print(
        "{} wins / {} tries in {} sec {}".format(
            wins, tries, total_time,
            "({} sec/try)".format(
                # can't divide by zero, which is falsey
                round(total_time / tries, 2)) if tries else ''
        )
    )

# only if we're running as a script, not if imported as module
if __name__ == "__main__":
    play(maximum_figure=12)