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05-data-classes/dataclass/hackerclub.py

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+# tag::DOCTESTS[]
+"""
+``HackerClubMember`` objects accept an optional ``handle`` argument::
+
+    >>> anna = HackerClubMember('Anna Ravenscroft', handle='AnnaRaven')
+    >>> anna
+    HackerClubMember(name='Anna Ravenscroft', guests=[], handle='AnnaRaven')
+
+If ``handle`` is ommitted, it's set to the first part of the member's name::
+
+    >>> leo = HackerClubMember('Leo Rochael')
+    >>> leo
+    HackerClubMember(name='Leo Rochael', guests=[], handle='Leo')
+
+Members must have a unique handle. The following ``leo2`` will not be created,
+because its ``handle`` would be 'Leo', which was taken by ``leo``::
+
+    >>> leo2 = HackerClubMember('Leo DaVinci')
+    Traceback (most recent call last):
+      ...
+    ValueError: handle 'Leo' already exists.
+
+To fix, ``leo2`` must be created with an explicit ``handle``::
+
+    >>> leo2 = HackerClubMember('Leo DaVinci', handle='Neo')
+    >>> leo2
+    HackerClubMember(name='Leo DaVinci', guests=[], handle='Neo')
+"""
+# end::DOCTESTS[]
+
+# tag::HACKERCLUB[]
+from dataclasses import dataclass
+from club import ClubMember
+
+@dataclass
+class HackerClubMember(ClubMember):                         # <1>
+
+    all_handles = set()                                     # <2>
+
+    handle: str = ''                                        # <3>
+
+    def __post_init__(self):
+        cls = self.__class__                                # <4>
+        if self.handle == '':                               # <5>
+            self.handle = self.name.split()[0]
+        if self.handle in cls.all_handles:                  # <6>
+            msg = f'handle {self.handle!r} already exists.'
+            raise ValueError(msg)
+        cls.all_handles.add(self.handle)                    # <7>
+# end::HACKERCLUB[]