Stack implementation in Python

PyStack.py

class PyStack():
    def __init__(self):
        self._items = []

    def push(self, item):
        self._items.append(item)

    def pop(self):
        if not self.isEmpty():
            return self._items.pop()
        else:
            return IndexError('Invalid pop: stack is empty.')

    def isEmpty(self):
        return True if len(self._items) == 0 else False

    def peek(self):
        if not self.isEmpty():
            return self._items[-1]
        else:
            return IndexError('Invalid peek: stack is empty.')

    def __repr__(self):
        return "[{}]".format(", ".join(map(str, self._items)))

    def __iter__(self):
        for i in self._items:
            yield i