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canon.py

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+class Canon:
+    """Keeps canonical instances of hashable objects to save space when there
+       will be many equal copies made for whatever reason.
+
+       When webscraping, for example, there may be thousands of repetitions of
+       the same text that you get from pages that come from thousands of
+       separate requests. Space can be saved by simply filtering each likely-
+       duplicated instance through a collection of canonical copies of that
+       type of thing.
+
+       This filtering process maps each thing onto its canonical equivalent
+       (an object instance that is equal to it) from a cache. If and when the
+       thing in question is not already present in the cache, the thing itself
+       is added to the cache and then the thing is mapped onto itself."""
+
+    def __init__(self, things=None):
+        self.storage = {}
+        if things:
+            self.multi(things)
+
+    def single(self, thing):
+        """:returns: the canonical equivalent instance of `thing`"""
+        try:
+            return self.storage[thing]
+        except KeyError:
+            self.storage[thing] = thing
+            return thing
+
+    def multi(self, things):
+        """:returns: a collection of canonical instances of elements of `things`"""
+        return type(things)(self.single(thing) for thing in things)