2020-2-14(36)

#[137]案例学习

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):
        '''移动到行首'''
        while self.document.characters[self.position-1] != "\n":
            self.position -= 1
            if self.position == 0:
                break
                
    def end(self):
        '''移动到行尾'''
        while self.position < len(self.document.characters) and \
               self.document.characters[self.position] != "\n":
            self.position += 1
            
class Document:
    def __init__(self):
        self.characters = []
        self.cursor = Cursor(self)
        self.filename = ""
        
    def insert(self, chr):
        self.characters.insert(self.cursor, chr)
        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)