dynamic attributes, descriptors and first concurrency examples

metaprog/oscon-schedule/data/osconfeed.json

@@ -1,4 +1,4 @@
-
+
 
 
 
@@ -11,7 +11,7 @@
         "serial": 33451,
         "name": "Migrating to the Web Using Dart and Polymer - A Guide for Legacy OOP Developers",
         "event_type": "40-minute conference session",
-        
+
         "time_start": "2014-07-23 17:00:00",
         "time_stop": "2014-07-23 17:40:00",
         "venue_serial": 1458,
@@ -13304,4 +13304,4 @@
 
  
 
-
+

metaprog/oscon-schedule/demo_schedule2.py

@@ -0,0 +1,23 @@
+import shelve
+
+from schedule2 import DB_NAME, CONFERENCE, load_db
+from schedule2 import DbRecord, Event
+
+with shelve.open(DB_NAME) as db:
+    if CONFERENCE not in db:
+        load_db(db)
+    
+    DbRecord.set_db(db)
+    event = DbRecord.fetch('event.33950')
+    print(event)
+    print(event.venue)
+    print(event.venue.name)
+    for spkr in event.speakers:
+        print('{0.serial}: {0.name}'.format(spkr))
+        
+    print(repr(Event.venue))
+    
+    event2 = DbRecord.fetch('event.33451')
+    print(event2)
+    print(event2.fetch)
+    print(event2.venue)

metaprog/oscon-schedule/explore1.py

@@ -9,14 +9,21 @@ explore1.py: Script to explore the OSCON schedule feed
     357
     >>> sorted(feed.Schedule.keys())  # <3>
     ['conferences', 'events', 'speakers', 'venues']
-    >>> feed.Schedule.speakers[-1].name  # <4>
+    >>> for key, value in sorted(feed.Schedule.items()): # <4>
+    ...     print('{:3} {}'.format(len(value), key))
+    ...
+      1 conferences
+    484 events
+    357 speakers
+     53 venues
+    >>> feed.Schedule.speakers[-1].name  # <5>
     'Carina C. Zona'
-    >>> talk = feed.Schedule.events[40]  # <5>
+    >>> talk = feed.Schedule.events[40]  # <6>
     >>> talk.name
     'There *Will* Be Bugs'
-    >>> talk.speakers  # <6>
+    >>> talk.speakers  # <7>
     [3471, 5199]
-    >>> talk.flavor  # <7>
+    >>> talk.flavor  # <8>
     Traceback (most recent call last):
       ...
     KeyError: 'flavor'
@@ -34,13 +41,13 @@ class FrozenJSON:
     """
 
     def __init__(self, mapping):
-        self._data = dict(mapping)  # <1>
+        self.__data = dict(mapping)  # <1>
 
     def __getattr__(self, name):  # <2>
-        if hasattr(self._data, name):
-            return getattr(self._data, name)  # <3>
+        if hasattr(self.__data, name):
+            return getattr(self.__data, name)  # <3>
         else:
-            return FrozenJSON.build(self._data[name])  # <4>
+            return FrozenJSON.build(self.__data[name])  # <4>
 
     @classmethod
     def build(cls, obj):  # <5>

metaprog/oscon-schedule/explore2.py

@@ -40,11 +40,11 @@ class FrozenJSON:
             return arg
 
     def __init__(self, mapping):
-        self._data = dict(mapping)
+        self.__data = dict(mapping)
 
     def __getattr__(self, name):
-        if hasattr(self._data, name):
-            return getattr(self._data, name)
+        if hasattr(self.__data, name):
+            return getattr(self.__data, name)
         else:
-            return FrozenJSON(self._data[name])  # <4>
+            return FrozenJSON(self.__data[name])  # <4>
 # END EXPLORE2

metaprog/oscon-schedule/schedule1.py

@@ -10,10 +10,8 @@ schedule1.py: traversing OSCON schedule data
     >>> speaker = db['speaker.3471']  # <4>
     >>> type(speaker)  # <5>
     <class 'schedule1.Record'>
-    >>> speaker.name  # <6>
-    'Anna Martelli Ravenscroft'
-    >>> speaker.twitter
-    'annaraven'
+    >>> speaker.name, speaker.twitter  # <6>
+    ('Anna Martelli Ravenscroft', 'annaraven')
     >>> db.close()  # <7>
 
 # END SCHEDULE1_DEMO
@@ -23,7 +21,7 @@ schedule1.py: traversing OSCON schedule data
 # BEGIN SCHEDULE1
 import warnings
 
-import osconfeed
+import osconfeed  # <1>
 
 DB_NAME = 'data/schedule1_db'
 CONFERENCE = 'conference.115'
@@ -31,17 +29,17 @@ CONFERENCE = 'conference.115'
 
 class Record:
     def __init__(self, **kwargs):
-        self.__dict__.update(kwargs)  # <1>
+        self.__dict__.update(kwargs)  # <2>
 
 
 def load_db(db):
-    raw_data = osconfeed.load()  # <2>
+    raw_data = osconfeed.load()  # <3>
     warnings.warn('loading ' + DB_NAME)
-    for collection, rec_list in raw_data['Schedule'].items():  # <3>
-        record_type = collection[:-1]  # <4>
+    for collection, rec_list in raw_data['Schedule'].items():  # <4>
+        record_type = collection[:-1]  # <5>
         for record in rec_list:
-            key = '{}.{}'.format(record_type, record['serial'])  # <5>
-            record['serial'] = key  # <6>
-            db[key] = Record(**record)  # <7>
+            key = '{}.{}'.format(record_type, record['serial'])  # <6>
+            record['serial'] = key  # <7>
+            db[key] = Record(**record)  # <8>
 
 # END SCHEDULE1

metaprog/oscon-schedule/schedule2.py

@@ -56,15 +56,15 @@ class MissingDatabaseError(RuntimeError):
 
 class DbRecord(Record):  # <2>
 
-    _db = None  # <3>
+    __db = None  # <3>
 
     @staticmethod  # <4>
     def set_db(db):
-        DbRecord._db = db  # <5>
+        DbRecord.__db = db  # <5>
 
     @staticmethod  # <6>
     def get_db():
-        return DbRecord._db
+        return DbRecord.__db
 
     @classmethod  # <7>
     def fetch(cls, ident):
@@ -93,22 +93,23 @@ class Event(DbRecord):  # <1>
     @property
     def venue(self):
         key = 'venue.{}'.format(self.venue_serial)
-        return self.fetch(key)  # <2>
+        return self.__class__.fetch(key)  # <2>
 
     @property
     def speakers(self):
         if not hasattr(self, '_speaker_objs'):  # <3>
             spkr_serials = self.__dict__['speakers']  # <4>
-            self._speaker_objs = [self.fetch('speaker.{}'.format(key))
-                                  for key in spkr_serials]  # <5>
-        return self._speaker_objs  # <6>
+            fetch = self.__class__.fetch  # <5>
+            self._speaker_objs = [fetch('speaker.{}'.format(key))
+                                  for key in spkr_serials]  # <6>
+        return self._speaker_objs  # <7>
 
     def __repr__(self):
-        if hasattr(self, 'name'):  # <7>
+        if hasattr(self, 'name'):  # <8>
             cls_name = self.__class__.__name__
             return '<{} {!r}>'.format(cls_name, self.name)
         else:
-            return super().__repr__()  # <8>
+            return super().__repr__()  # <9>
 # END SCHEDULE2_EVENT
 
 
@@ -127,5 +128,5 @@ def load_db(db):
         for record in rec_list:  # <7>
             key = '{}.{}'.format(record_type, record['serial'])
             record['serial'] = key
-            db[key] = factory(**record)  # <>
+            db[key] = factory(**record)  # <8>
 # END SCHEDULE2_LOAD

metaprog/prop_inheritance.py

@@ -0,0 +1,29 @@
+"""
+Alex Martelli, _Python in a Nutshell, 2e._ (O'Reilly, 2006), p. 101
+
+==========================
+Properties and inheritance
+==========================
+
+Properties are inherited normally, just like any other attribute.
+However, there’s a little trap for the unwary: the methods called
+upon to access a property are those that are defined in the class
+in which the property itself is defined, without intrinsic use of
+further overriding that may happen in subclasses. For example:
+"""
+
+class B(object):
+
+    def f(self):
+        return 23
+
+    g = property(f)
+
+class C(B):
+
+    def f(self):
+        return 42
+
+c = C()
+
+print(c.g) # prints 23, not 42

metaprog/special_attrs.py

@@ -0,0 +1,44 @@
+
+'''
+4.13. Special Attributes
+
+The implementation adds a few special read-only attributes to
+several object types, where they are relevant.
+
+Some of these are not reported by the dir() built-in function.
+
+https://docs.python.org/3/library/stdtypes.html#special-attributes
+'''
+
+
+obj_attrs = {'__dict__', '__class__'}
+
+cls_data_attrs = {'__slots__', '__bases__', '__name__', '__qualname__', '__mro__'}
+
+cls_methods = {'mro', '__subclasses__'}
+
+cls_attrs = cls_data_attrs | cls_methods
+
+
+an_object = object()
+
+class EmptyClass():
+    pass
+
+an_instance = EmptyClass()
+
+class EmptySlots():
+    __slots__ = ()
+
+a_slots_instance = EmptySlots()
+
+
+objs = EmptyClass, EmptySlots, an_object, an_instance, a_slots_instance
+
+for obj in objs:
+    print('-' * 60)
+    print(repr(obj), ':', type(obj))
+    dir_obj = set(dir(obj))
+    print('obj_attrs not listed:', sorted(obj_attrs - dir_obj))
+    print('all cls_attrs       :', sorted(cls_attrs))
+    print('cls_attrs not listed:', sorted(cls_attrs - dir_obj))