判断10步能不能回到原点

题目描述：

# You live in the city of Cartesia where all roads are laid out in a perfect grid.
# You arrived ten minutes too early to an appointment, so you decided
# to take the opportunity to go for a short walk. The city provides
# its citizens with a Walk Generating App on their phones --
# everytime you press the button it sends you an array of
# one-letter strings representing directions to walk
# (eg. ['n', 's', 'w', 'e']). You always walk only a single block in a direction
# and you know it takes you one minute to traverse one city block,
# so create a function that will return true if the walk the app gives you will
# take you exactly ten minutes (you don't want to be early or late!) and will, of course,
# return you to your starting point. Return false otherwise.

我的解答：

def is_valid_walk(walk):
    if len(walk) != 10:
        return False
    if walk.count('n') == walk.count('s'):
        if walk.count('w') == walk.count('e'):
            return True
    return False