learning-by-doing/python_3_oop/chapter05/editor.py

class Document:

    def __init__(self):
        self.characters = []
        self.cursor = Cursor(self)
        self.filename = ""

    def insert(self, character):
        self.characters.insert(self.cursor.position, character)
        self.cursor.forward()

    def delete(self):
        del self.characters[self.cursor.position]

    def save(self):
        f = open(self.filename, "w")
        f.write("".join(self.characters))
        f.close()

    @property
    def string(self):
        return "".join(self.characters)


class Cursor:

    def __init__(self, document):
        self.document = document
        self.position = 0

    def forward(self):
        self.position += 1

    def back(self):
        self.position -= 1

    def home(self):
        while self.document.characters[self.position - 1] != "\n":
            self.position -= 1
            if self.position == 0:
                # got to beginning of file before newline
                break

    def end(self):
        while (self.position < len(self.document.characters) and
               self.document.characters[self.position] != "\n"):
            self.position += 1