python_solutions.py

# my solutions to https://technology.jana.com/2016/04/26/challenge-your-python-knowledge/

def challenge_1():
    ################
    # solution #1
    #
    # an open file handle will always count as "True", but the file might have
    # nothing in it.
    mystery = open('/dev/null', 'r')
    ################

    def print_stuff(stuff):
        if stuff:
            print "Printing some stuff"
            for x in stuff:
                print x
        else:
            print "Nothing to print"

    print_stuff(mystery)

    # output:
    # Printing some stuff


def challenge_2():
    ################
    # solution #2
    #
    # because floating-point numbers only have about 15 digits of precision,
    # adding 1 to 1e16 gives no change, and adding 1e16 to 1e33 gives no
    # change.
    mystery1 = 1e16
    mystery2 = 1e33
    ################

    def sum_some_nums(low, high):
        total = 0
        while low <= high:
            total += low
            low += 1
        return total

    # Make sure we are using valid numeric values
    assert float('-inf') < mystery1 < float('inf')
    assert float('-inf') < mystery2 < float('inf')

    print sum_some_nums(mystery1, mystery2)

    # result:
    # Program never terminates


def challenge_3():
    ################
    # solution #3
    #
    # if the dictionaries reference each other, you'll get this recursion
    # exception.
    mystery1 = {}
    mystery2 = {'foo': mystery1}
    mystery1['foo'] = mystery2
    ################

    # These are exactly dicts, not subclasses of dict
    assert type(mystery1) is dict
    assert type(mystery2) is dict

    print mystery1 == mystery2

    # result:
    # RuntimeError: maximum recursion depth exceeded in cmp


def challenge_4():
    ################
    # solution #4
    #
    # dictionaries are inherently unordered, and dictionaries with the same
    # contents can iterate in different orders (and str() iterates over the
    # elements). here we grow the dictionary first to force it to
    # re-optimize at a different size, then shrink it back down.
    size = 100
    mystery1 = {i: True for i in range(size)}
    mystery2 = {'foo': True, 'bar': True}
    mystery1.update(mystery2)
    for i in range(size):
        del mystery1[i]
    ################

    assert type(mystery1) is dict
    assert type(mystery2) is dict

    assert str(mystery1) != str(mystery2)
    assert mystery1 == mystery2

    print "All checks passed"

    # output:
    # All checks passed