python_answers.py

"""
Answers to shopping list, generation, iteration, decoration exercises posted
"""


def shopping_list():
    """
    Exercise: shopping list

        using while True: and input() create a shopping list interface allowing a user to enter multiple items then type DONE to exit
        add a command to delete the last item in the list
        add a command to print the current list
        add a commands to save the list to a file and load from a file
    """
    items = []

    def show():
        print('\n'.join(items))

    while True:
        item = input('What to buy/DONE/DEL/SHOW/SAVE/LOAD? ')
        if item == 'DONE':
            break
        elif item == 'DEL':
            try:
                del items[-1]
            except IndexError:
                print('nothing to delete')
        elif item == 'SHOW':
            show()
        elif item == 'SAVE':
            with open('shopping.txt', 'w') as f:
                f.write('\n'.join(items))
        elif item == 'LOAD':
            with open('shopping.txt') as f:
                items = f.read().split('\n')
        else:
            items.append(item)

    show()


def number_sequence():
    """
    Exercise: generation, iteration, decoration

    create a generator that produces the sequence: 1, 2, 1, 2, 2, 1, 2, 2, 2, ⋯
    """
    n = 1
    while True:
        yield 1
        for i in range(n):
            yield 2
        n += 1
    # NOTE: this generator never exits


def five_from_number_sequence():
    """
    write code that will skip the first element of the generator above then print the next 5 elements
    """
    seq = number_sequence()
    next(seq)
    for i in range(5):
        print(next(seq))


def noisy_decorator(fn):
    """
    create a decorator that will print all arguments passed to a function and its return value
    """
    def wrapper(*args, **kwargs):
        print('arguments passed to', fn.__name__, ':', args, kwargs)
        rval = fn(*args, **kwargs)
        print('return value:', rval)
        return rval
    return wrapper