# VendingMachine Example
# Create a VendingMachine class with private
# fields _num_quarters, _num_candy_bars,
# and public methods deposit_quarter,
# dispense_candy_bar.

# This vending machine dispenses one type of
# candy bar, which is paid for with 3 quarters.

class VendingMachine:

    def __init__(self):
        self._num_candy_bars = 3
        self._num_quarters = 0

    def insert_quarter(self):
        self._num_quarters += 1
        return "Quarter inserted."

    def dispense_candy_bar(self):
        if self._num_quarters >= 3 and \
            self._num_candy_bars > 0:
            self._num_quarters = 0
            self._num_candy_bars -= 1
            return "Candy bar dispensed."
        else:
            return "VM out of candy bars."

    def __str__(self):
        return f"{self._num_candy_bars} " + \
               f"{self._num_quarters}"