added case study of chapter 05

python_3_oop/chapter05/editor.py

@@ -0,0 +1,47 @@
+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