renumbering chapters >= 19

22-dyn-attr-prop/blackknight.py

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+"""
+This class is inspired by the Black Knight scene in the movie
+"Monty Python and the Holy Grail", where King Arthur fights the
+Black Knight, slicing off his arms and legs, but the knight
+refuses to concede defeat.
+
+# tag::BLACK_KNIGHT_DEMO[]
+    >>> knight = BlackKnight()
+    >>> knight.member
+    next member is:
+    'an arm'
+    >>> del knight.member
+    BLACK KNIGHT (loses an arm) -- 'Tis but a scratch.
+    >>> del knight.member
+    BLACK KNIGHT (loses another arm) -- It's just a flesh wound.
+    >>> del knight.member
+    BLACK KNIGHT (loses a leg) -- I'm invincible!
+    >>> del knight.member
+    BLACK KNIGHT (loses another leg) -- All right, we'll call it a draw.
+
+# end::BLACK_KNIGHT_DEMO[]
+"""
+
+# tag::BLACK_KNIGHT[]
+class BlackKnight:
+
+    def __init__(self):
+        self.phrases = [
+            ('an arm', "'Tis but a scratch."),
+            ('another arm', "It's just a flesh wound."),
+            ('a leg', "I'm invincible!"),
+            ('another leg', "All right, we'll call it a draw.")
+        ]
+
+    @property
+    def member(self):
+        print('next member is:')
+        return self.phrases[0][0]
+
+    @member.deleter
+    def member(self):
+        member, text = self.phrases.pop(0)
+        print(f'BLACK KNIGHT (loses {member}) -- {text}')
+# end::BLACK_KNIGHT[]