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PythonCHBPythonCHB
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got the presentation in good shape -- added examples, etc.
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-286
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‎_downloads/CircularReferenceExample.ipynb‎

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‎_downloads/circular.py‎

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#!/usr/bin/env python
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# -*- coding: utf-8 -*-
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import sys
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import weakref
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import gc
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deleted_object_messages = []
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class MyChild(object):
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def __init__(self, parent):
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self.parent = parent
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#self.parent = weakref.ref(parent)
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#self.parent = weakref.proxy(parent)
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## store some data so it will use appreciable memory
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## multiply by 1234 to avoid interning
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self.data = [1234*i for i in range(100000)]
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def __del__(self):
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deleted_object_messages.append( ('MyChild deleted', id(self)) )
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class MyParent(object):
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def __init__(self):
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self.children = []
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def addChild(self):
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child = MyChild(self)
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self.children.append(child)
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return child
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def __del__(self):
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deleted_object_messages.append( ('MyParent deleted', id(self)) )
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if __name__ == "__main__":
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p = MyParent()
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print "refcount for p:", sys.getrefcount(p)
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assert sys.getrefcount(p) == 2
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a = p.addChild()
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a2 = p.addChild()
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print "refcount for p after adding an two children:", sys.getrefcount(p)
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assert sys.getrefcount(p) == 2
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print "p's children:", p.children
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assert len(p.children) == 2
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print " a is:", a
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print "a's parent:", a.parent
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print "a's parent's children:", a.parent.children
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assert a is a.parent.children[0]
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assert a2 is a.parent.children[1]
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print "a's refcount:", sys.getrefcount(a)
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assert sys.getrefcount(a) == 3
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print "a2's refcount:", sys.getrefcount(a2)
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assert sys.getrefcount(a2) == 3
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del p
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print "after deleting p:"
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print "a's refcount:", sys.getrefcount(a)
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assert sys.getrefcount(a) == 2
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print "a2's refcount:", sys.getrefcount(a2)
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assert sys.getrefcount(a2) == 2
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print "deleting a:"
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id_a = id(a)
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del a
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print deleted_object_messages
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assert deleted_object_messages[-1][0] == 'MyChild deleted'
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assert deleted_object_messages[-1][1] == id_a
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print "deleting a2:"
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id_a2 = id(a2)
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del a2
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print deleted_object_messages
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assert deleted_object_messages[-1][0] == 'MyChild deleted'
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assert deleted_object_messages[-1][1] == id_a2
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‎_downloads/mem_check.py‎

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"""
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mem_check.py
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functions for getting memoroy use of the current python process
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Windows and *nix versions
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USAGE:
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amount = get_mem_use(units='MB') # options are KB, MB, GB
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"""
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import sys
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div = {'GB': 1024*1024*1024,
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'MB': 1024*1024,
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'KB': 1024,
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}
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if sys.platform.startswith('win'):
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"""
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Functions for getting memory usage of Windows processes.
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from:
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http://code.activestate.com/recipes/578513-get-memory-usage-of-windows-processes-using-getpro/
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get_mem_use(units='MB') is the one to get memory use for the current process.
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"""
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import ctypes
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from ctypes import wintypes
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GetCurrentProcess = ctypes.windll.kernel32.GetCurrentProcess
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GetCurrentProcess.argtypes = []
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GetCurrentProcess.restype = wintypes.HANDLE
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SIZE_T = ctypes.c_size_t
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class PROCESS_MEMORY_COUNTERS_EX(ctypes.Structure):
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_fields_ = [
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('cb', wintypes.DWORD),
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('PageFaultCount', wintypes.DWORD),
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('PeakWorkingSetSize', SIZE_T),
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('WorkingSetSize', SIZE_T),
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('QuotaPeakPagedPoolUsage', SIZE_T),
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('QuotaPagedPoolUsage', SIZE_T),
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('QuotaPeakNonPagedPoolUsage', SIZE_T),
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('QuotaNonPagedPoolUsage', SIZE_T),
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('PagefileUsage', SIZE_T),
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('PeakPagefileUsage', SIZE_T),
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('PrivateUsage', SIZE_T),
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]
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GetProcessMemoryInfo = ctypes.windll.psapi.GetProcessMemoryInfo
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GetProcessMemoryInfo.argtypes = [
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wintypes.HANDLE,
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ctypes.POINTER(PROCESS_MEMORY_COUNTERS_EX),
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wintypes.DWORD,
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]
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GetProcessMemoryInfo.restype = wintypes.BOOL
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def get_current_process():
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"""Return handle to current process."""
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return GetCurrentProcess()
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def get_memory_info(process=None):
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"""Return Win32 process memory counters structure as a dict."""
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if process is None:
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process = get_current_process()
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counters = PROCESS_MEMORY_COUNTERS_EX()
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ret = GetProcessMemoryInfo(process, ctypes.byref(counters),
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ctypes.sizeof(counters))
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if not ret:
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raise ctypes.WinError()
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info = dict((name, getattr(counters, name))
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for name, _ in counters._fields_)
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return info
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def get_mem_use(units='MB'):
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"""
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returns the total memory use of the current python process
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:param units='MB': the units you want the reslut in. Options are:
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'GB', 'MB', 'KB'
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"""
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info = get_memory_info()
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return info['PrivateUsage'] / float(div[units])
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else: # for posix systems only tested on OS-X for now
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def get_mem_use(units='MB'):
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"""
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returns the total memory use of the current python process
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:param units='MB': the units you want the reslut in. Options are:
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'GB', 'MB', 'KB'
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"""
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import resource
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#useage = resource.getrusage(resource.RUSAGE_SELF).ru_maxrss
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div = {'GB': 1024*1024*1024,
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'MB': 1024*1024,
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'KB': 1024,
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}
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return resource.getrusage(resource.RUSAGE_SELF).ru_maxrss / float(div[units])

‎_downloads/memcount.py‎

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#!/usr/bin/env python
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# -*- coding: utf-8 -*-
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"""
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a simple test of a circular reference that gc.collect() will not clean up.
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And watch the memory grow!
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"""
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import sys
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import gc
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import weakref
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import mem_check
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class MyChild(object):
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def __init__(self, parent):
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self.parent = parent
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# if a weak ref is used, then no memory leak.
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#self.parent = weakref.proxy(parent)
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## store some data so it will use appreciable memory
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## multiply by 1234 to reduce interning
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self.data = [1234*i for i in range(100000)]
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def __del__(self):
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""" __del__ defined to defeat GC"""
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print 'MyChild deleted', id(self)
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class MyParent(object):
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def __init__(self):
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self.children = []
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def addChild(self):
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child = MyChild(self)
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self.children.append(child)
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return child
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def __del__(self):
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""" __del__ defined to defeat GC"""
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print 'MyParent deleted', id(self)
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if __name__ == "__main__":
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# create a bunch in a loop:
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for i in range(50):
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print "iteration:", i
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p = MyParent()
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p.addChild()
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p.addChild()
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p.addChild()
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print "ref count:", sys.getrefcount(p)
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print "mem_use: %f MB"%mem_check.get_mem_use()
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del p
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gc.collect()

‎_downloads/simple_circular.py‎

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#!/usr/bin/env python
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"""
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Simple contrived example of circular reference counting
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"""
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import sys
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import di
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import gc
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l1 = [1,]
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l2 = [2,]
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l1_id = id(l1)
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l2_id = id(l2)
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print "initial ref counts:"
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print "l1:", sys.getrefcount(l1)
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print "l2:", sys.getrefcount(l2)
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print "now add the circular references:"
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l1.append(l2)
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l2.append(l1)
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print "ref counts after the circular reference is added"
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print "l1:", sys.getrefcount(l1)
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print "l2:", sys.getrefcount(l2)
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print "delete one"
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del l1
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print "l1:", sys.getrefcount(l2)
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print "delete the other"
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del l2
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print "are they still there?"
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print "l1's refcount:", di.ref_by_id(l1_id)
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print "l2's refcount:", di.ref_by_id(l2_id)
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print "-- yes they are!"
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print "now run the garbage collector"
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print "It collected:", gc.collect(), "objects"
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print "ref counts now???"
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print "l1's refcount:", di.ref_by_id(l1_id)
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print "l2's refcount:", di.ref_by_id(l2_id)
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print "yup -- they'll get cleaned up"
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‎_sources/index.txt‎

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.. ifslides::
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+----------------------+-----------------------+
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| Topics: | Materials: |
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+======================+=======================+
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| .. toctree:: | .. toctree:: |
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| :maxdepth: 1 | :maxdepth: 1 |
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| | |
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| session01 | supplements/index |
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| session02 | |
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| session03 | |
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| session04 | |
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| session05 | |
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| session06 | |
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| session07 | |
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| session08 | |
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+----------------------+-----------------------+
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+----------------------+
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| Topics: |
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+======================+
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| .. toctree:: |
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| :maxdepth: 1 |
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| |
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| weak_references |
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+----------------------+
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.. ifnotslides::
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weak_references
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Materials:
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----------
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.. toctree::
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:maxdepth: 2
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supplements/index
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.. rst-class:: credit
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These materials copyright Christopher H. Barker
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Licenced under the Creative Commons Attribution-ShareAlike 4.0 International Public License.
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Licensed under the Creative Commons Attribution-ShareAlike 4.0 International Public License.
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https://creativecommons.org/licenses/by-sa/4.0/legalcode
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