From f59e962b494905796d5f0e74e7a97274c04ff19f Mon Sep 17 00:00:00 2001
From: Raymond Hettinger <python@rcn.com>
Date: Tue, 15 Jan 2008 20:52:42 +0000
Subject: [PATCH] Refactor if/elif chain for clarity and speed.  Remove
 dependency on subclasses having to implement _empty and _full.

---
 Doc/library/collections.rst |  8 ++++++
 Lib/Queue.py                | 53 ++++++++++++++++---------------------
 2 files changed, 31 insertions(+), 30 deletions(-)

diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst
index b10569b7173..de9bcbfae2d 100644
--- a/Doc/library/collections.rst
+++ b/Doc/library/collections.rst
@@ -535,6 +535,14 @@ faster versions that bypass error-checking::
         def _replace(self, _map=map, **kwds):
             return self._make(_map(kwds.get, ('x', 'y'), self))
 
+Note, subclasses should set ``__slots__`` to an empty tuple so that
+an instance dictionary will not be created and the memory overhead
+will be kept to zero.
+
+Note, subclasses should set ``__slots__`` to an empty tuple.  This
+reduces memory usage by 
+
+
 Subclassing is not useful for adding new, stored fields.  Instead, simply
 create a new named tuple type from the :attr:`_fields` attribute::
 
diff --git a/Lib/Queue.py b/Lib/Queue.py
index 79b0abf1418..ce340249b2b 100644
--- a/Lib/Queue.py
+++ b/Lib/Queue.py
@@ -23,6 +23,7 @@ class Queue:
             import threading
         except ImportError:
             import dummy_threading as threading
+        self.maxsize = maxsize
         self._init(maxsize)
         # mutex must be held whenever the queue is mutating.  All methods
         # that acquire mutex must release it before returning.  mutex
@@ -91,14 +92,14 @@ class Queue:
     def empty(self):
         """Return True if the queue is empty, False otherwise (not reliable!)."""
         self.mutex.acquire()
-        n = self._empty()
+        n = not self._qsize()
         self.mutex.release()
         return n
 
     def full(self):
         """Return True if the queue is full, False otherwise (not reliable!)."""
         self.mutex.acquire()
-        n = self._full()
+        n = 0 < self.maxsize == self._qsize()
         self.mutex.release()
         return n
 
@@ -115,21 +116,22 @@ class Queue:
         """
         self.not_full.acquire()
         try:
-            if not block:
-                if self._full():
-                    raise Full
-            elif timeout is None:
-                while self._full():
-                    self.not_full.wait()
-            else:
-                if timeout < 0:
-                    raise ValueError("'timeout' must be a positive number")
-                endtime = _time() + timeout
-                while self._full():
-                    remaining = endtime - _time()
-                    if remaining <= 0.0:
+            if self.maxsize > 0:
+                if not block:
+                    if self._qsize() == self.maxsize:
                         raise Full
-                    self.not_full.wait(remaining)
+                elif timeout is None:
+                    while self._qsize() == self.maxsize:
+                        self.not_full.wait()
+                elif timeout < 0:
+                    raise ValueError("'timeout' must be a positive number")
+                else:
+                    endtime = _time() + timeout
+                    while self._qsize() == self.maxsize:
+                        remaining = endtime - _time()
+                        if remaining <= 0.0:
+                            raise Full
+                        self.not_full.wait(remaining)
             self._put(item)
             self.unfinished_tasks += 1
             self.not_empty.notify()
@@ -158,16 +160,16 @@ class Queue:
         self.not_empty.acquire()
         try:
             if not block:
-                if self._empty():
+                if not self._qsize():
                     raise Empty
             elif timeout is None:
-                while self._empty():
+                while not self._qsize():
                     self.not_empty.wait()
+            elif timeout < 0:
+                raise ValueError("'timeout' must be a positive number")
             else:
-                if timeout < 0:
-                    raise ValueError("'timeout' must be a positive number")
                 endtime = _time() + timeout
-                while self._empty():
+                while not self._qsize():
                     remaining = endtime - _time()
                     if remaining <= 0.0:
                         raise Empty
@@ -192,20 +194,11 @@ class Queue:
 
     # Initialize the queue representation
     def _init(self, maxsize):
-        self.maxsize = maxsize
         self.queue = deque()
 
     def _qsize(self):
         return len(self.queue)
 
-    # Check whether the queue is empty
-    def _empty(self):
-        return not self.queue
-
-    # Check whether the queue is full
-    def _full(self):
-        return self.maxsize > 0 and len(self.queue) == self.maxsize
-
     # Put a new item in the queue
     def _put(self, item):
         self.queue.append(item)