Jython relies on the Java runtime so the JVM’s garbage collector is used. This difference can cause some subtle porting problems if your Python code depends on the behavior of the reference counting implementation.
Sometimes objects get stuck in tracebacks temporarily and hence are not deallocated when you might expect. Clear the tracebacks with:
import sys
sys.exc_clear()
sys.exc_traceback = sys.last_traceback = None
Tracebacks are used for reporting errors, implementing debuggers and related things. They contain a portion of the program state extracted during the handling of an exception (usually the most recent exception).
In the absence of circularities and tracebacks, Python programs need not explicitly manage memory.
Why doesn’t Python use a more traditional garbage collection scheme? For one thing, this is not a C standard feature and hence it’s not portable. (Yes, we know about the Boehm GC library. It has bits of assembler code for most common platforms, not for all of them, and although it is mostly transparent, it isn’t completely transparent; patches are required to get Python to work with it.)
Traditional GC also becomes a problem when Python is embedded into other applications. While in a standalone Python it’s fine to replace the standard malloc() and free() with versions provided by the GC library, an application embedding Python may want to have its own substitute for malloc() and free(), and may not want Python’s. Right now, Python works with anything that implements malloc() and free() properly.
In Jython, the following code (which is fine in CPython) will probably run out of file descriptors long before it runs out of memory:
for file in <very long list of files>:
f = open(file)
c = f.read(1)
Using the current reference counting and destructor scheme, each new assignment to f closes the previous file. Using GC, this is not guaranteed. If you want to write code that will work with any Python implementation, you should explicitly close the file; this will work regardless of GC:
for file in <very long list of files>:
f = open(file)
c = f.read(1)
f.close()
]]>
Some common situations that may prevent the reference count of an object from going to zero include: circular references between objects (e.g., a doubly-linked list or a tree data structure with parent and child pointers); a reference to the object on the stack frame of a function that caught an exception (the traceback stored in sys.exc_traceback keeps the stack frame alive); or a reference to the object on the stack frame that raised an unhandled exception in interactive mode (the traceback stored in sys.last_traceback keeps the stack frame alive).
鍙錛屾湁 __del__() 鍑芥暟鐨勫璞￠棿鐨勫驚鐜紩鐢ㄦ槸瀵艱嚧鍐呭瓨娉勬紡鐨勪富鍑躲傜壒鍒鏄庯細瀵規(guī)病鏈?__del__() 鍑芥暟鐨?Python 瀵硅薄闂寸殑寰幆寮曠敤錛屾槸鍙互琚嚜鍔ㄥ瀮鍦懼洖鏀舵帀鐨勩?br />
鏈?__del__() 鍑芥暟鐨勫璞￠棿鐨勫驚鐜紩鐢ㄦ槸瀵艱嚧鍐呭瓨娉勬紡鐨勪富鍑躲傜壒鍒鏄庯細瀵規(guī)病鏈?__del__() 鍑芥暟鐨?Python 瀵硅薄闂寸殑寰幆寮曠敤錛屾槸鍙互琚嚜鍔ㄥ瀮鍦懼洖鏀舵帀鐨勩傛墍浠ワ紝娌′粈涔堜簨錛屽崈涓囦笉瑕佽交鏄撳惎鐢╛_del__鎿嶄綔銆?br /> 濡備綍鐭ラ亾涓涓璞℃槸鍚﹀唴瀛樻硠婕忎簡鍛紵
鏂規(guī)硶涓銆佸綋浣犺涓轟竴涓璞″簲璇ヨ閿姣佹椂錛堝嵆寮曠敤璁℃暟涓?0錛夛紝鍙互閫氳繃 sys.getrefcount(obj) 鏉ヨ幏鍙栧璞＄殑寮曠敤璁℃暟錛屽茍鏍規(guī)嵁榪斿洖鍊兼槸鍚︿負 0 鏉ュ垽鏂槸鍚﹀唴瀛樻硠婕忋傚鏋滆繑鍥炵殑寮曠敤璁℃暟涓嶄負 0錛岃鏄庡湪姝ゅ埢瀵硅薄 obj 鏄笉鑳借鍨冨溇鍥炴敹鍣ㄥ洖鏀舵帀鐨勩?br /> 鏂規(guī)硶浜屻佷篃鍙互閫氳繃 Python 鎵╁睍妯″潡 gc 鏉ユ煡鐪嬩笉鑳藉洖鏀剁殑瀵硅薄鐨勮緇嗕俊鎭?br />
棣栧厛錛屾潵鐪嬩竴孌墊甯哥殑嫻嬭瘯浠ｇ爜錛?br />
#--------------- code begin --------------
# -*- coding: utf-8 -*-
import gc
import sys
class CGcLeak(object):
def __init__(self):
self._text = '#'*10
def __del__(self):
pass
def make_circle_ref():
_gcleak = CGcLeak()
# _gcleak._self = _gcleak # test_code_1
print '_gcleak ref count0:%d' % sys.getrefcount(_gcleak)
del _gcleak
try:
print '_gcleak ref count1:%d' % sys.getrefcount(_gcleak)
except UnboundLocalError:
print '_gcleak is invalid!'
def test_gcleak():
# Enable automatic garbage collection.
gc.enable()
# Set the garbage collection debugging flags.
gc.set_debug(gc.DEBUG_COLLECTABLE | gc.DEBUG_UNCOLLECTABLE | \
gc.DEBUG_INSTANCES | gc.DEBUG_OBJECTS)
print 'begin leak test...'
make_circle_ref()
print 'begin collect...'
_unreachable = gc.collect()
print 'unreachable object num:%d' % _unreachable
print 'garbage object num:%d' % len(gc.garbage)
if __name__ == '__main__':
test_gcleak()
#--------------- code end ----------------
鍦?test_gcleak() 涓紝璁劇疆鍨冨溇鍥炴敹鍣ㄨ皟璇曟爣蹇楀悗錛屽啀鐢?collect() 榪涜鍨冨溇鍥炴敹錛屾渶鍚庢墦鍗板嚭璇ユ鍨冨溇鍥炴敹鍙戠幇鐨勪笉鍙揪鐨勫瀮鍦懼璞℃暟鍜屾暣涓В閲婂櫒涓殑鍨冨溇瀵硅薄鏁般?br />
gc.garbage 鏄竴涓?list 瀵硅薄錛屽垪琛ㄩ」鏄瀮鍦炬敹闆嗗櫒鍙戠幇鐨勪笉鍙揪錛堝嵆鏄瀮鍦懼璞★級銆佷絾鍙堜笉鑳介噴鏀撅紙鍗充笉鑳藉洖鏀訛級鐨勫璞°傛枃妗ｆ弿榪頒負錛欰 list of objects which the collector found to be unreachable but could not be freed (uncollectable objects).
閫氬父錛実c.garbage 涓殑瀵硅薄鏄紩鐢ㄧ幆涓殑瀵硅薄銆傚洜涓?Python 涓嶇煡閬撴寜鐓т粈涔堟牱鐨勫畨鍏ㄦ搴忔潵璋冪敤鐜腑瀵硅薄鐨?__del__() 鍑芥暟錛屽鑷村璞″緇堝瓨媧誨湪 gc.garbage 涓紝閫犳垚鍐呭瓨娉勬紡銆傚鏋滅煡閬撲竴涓畨鍏ㄧ殑嬈″簭錛岄偅涔堝氨鎵撶牬寮曠敤鐜紝鍐嶆墽琛?del gc.garbage[:] 錛屼互娓呯┖鍨冨溇瀵硅薄鍒楄〃銆?br />
涓婃浠ｇ爜杈撳嚭涓猴紙#鍚庡瓧絎︿覆涓虹瑪鑰呮墍鍔犳敞閲婏級錛?br /> #-----------------------------------------
begin leak test...
# 鍙橀噺 _gcleak 鐨勫紩鐢ㄨ鏁頒負 2.
_gcleak ref count0:2
# _gcleak 鍙樹負涓嶅彲杈?unreachable)鐨勯潪娉曞彉閲?
_gcleak is invalid!
# 寮濮嬪瀮鍦懼洖鏀?br /> begin collect...
# 鏈鍨冨溇鍥炴敹鍙戠幇鐨勪笉鍙揪鐨勫瀮鍦懼璞℃暟涓?0.
unreachable object num:0
# 鏁翠釜瑙ｉ噴鍣ㄤ腑鐨勫瀮鍦懼璞℃暟涓?0.
garbage object num:0
#-----------------------------------------
鍙 _gcleak 瀵硅薄鐨勫紩鐢ㄨ鏁版槸姝ｇ‘鐨勶紝涔熸病鏈変換浣曞璞″彂鐢熷唴瀛樻硠婕忋?br />
濡傛灉涓嶆敞閲婃帀 make_circle_ref() 涓殑 test_code_1 璇彞錛?br /> _gcleak._self = _gcleak
涔熷氨鏄 _gcleak 褰㈡垚涓涓嚜宸卞鑷繁鐨勫驚鐜紩鐢ㄣ傚啀榪愯涓婅堪浠ｇ爜錛岃緭鍑虹粨鏋滃氨鍙樻垚錛?br /> #-----------------------------------------
begin leak test...
_gcleak ref count0:3
_gcleak is invalid!
begin collect...
# 鍙戠幇鍙互鍥炴敹鐨勫瀮鍦懼璞? 鍦板潃涓?012AA090錛岀被鍨嬩負 CGcLeak.
gc: uncollectable <CGcLeak 012AA090>
gc: uncollectable <dict 012AC1E0>
unreachable object num:2
#!! 涓嶈兘鍥炴敹鐨勫瀮鍦懼璞℃暟涓?1錛屽鑷村唴瀛樻硠婕忥紒
garbage object num:1
#-----------------------------------------
鍙 <CGcLeak 012AA090> 瀵硅薄鍙戠敓浜嗗唴瀛樻硠婕忥紒錛佽屽鍑虹殑 dict 鍨冨溇灝辨槸娉勬紡鐨?_gcleak 瀵硅薄鐨勫瓧鍏革紝鎵撳嵃鍑哄瓧鍏鎬俊鎭負:
{'_self': <__main__.CGcLeak object at 0x012AA090>, '_text': '##########'}
闄や簡瀵硅嚜宸辯殑寰幆寮曠敤錛屽涓璞￠棿鐨勫驚鐜紩鐢ㄤ篃浼氬鑷村唴瀛樻硠婕忋傜畝鍗曚婦渚嬪涓嬶細
#--------------- code begin --------------
class CGcLeakA(object):
def __init__(self):
self._text = '#'*10
def __del__(self):
pass
class CGcLeakB(object):
def __init__(self):
self._text = '*'*10
def __del__(self):
pass
def make_circle_ref():
_a = CGcLeakA()
_b = CGcLeakB()
_a._b = _b # test_code_2
_b._a = _a # test_code_3
print 'ref count0:a=%d b=%d' % \
(sys.getrefcount(_a), sys.getrefcount(_b))
# _b._a = None # test_code_4
del _a
del _b
try:
print 'ref count1:a=%d' % sys.getrefcount(_a)
except UnboundLocalError:
print '_a is invalid!'
try:
print 'ref count2:b=%d' % sys.getrefcount(_b)
except UnboundLocalError:
print '_b is invalid!'
#--------------- code end ----------------
榪欐嫻嬭瘯鍚庤緭鍑虹粨鏋滀負錛?br /> #-----------------------------------------
begin leak test...
ref count0:a=3 b=3
_a is invalid!
_b is invalid!
begin collect...
gc: uncollectable <CGcLeakA 012AA110>
gc: uncollectable <CGcLeakB 012AA0B0>
gc: uncollectable <dict 012AC1E0>
gc: uncollectable <dict 012AC0C0>
unreachable object num:4
garbage object num:2
#-----------------------------------------
鍙 _a,_b 瀵硅薄閮藉彂鐢熶簡鍐呭瓨娉勬紡銆傚洜涓轟簩鑰呮槸寰幆寮曠敤錛屽瀮鍦懼洖鏀跺櫒涓嶇煡閬撹濡備綍鍥炴敹錛屼篃灝辨槸涓嶇煡閬撹棣栧厛璋冪敤閭ｄ釜瀵硅薄鐨?__del__() 鍑芥暟銆?br />
閲囩敤浠ヤ笅浠諱竴鏂規(guī)硶錛屾墦鐮寸幆鐘跺紩鐢紝灝卞彲浠ラ伩鍏嶅唴瀛樻硠婕忥細
[1] 娉ㄩ噴鎺?make_circle_ref() 涓殑 test_code_2 璇彞錛?br /> [2] 娉ㄩ噴鎺?make_circle_ref() 涓殑 test_code_3 璇彞錛?br /> [3] 鍙栨秷瀵?make_circle_ref() 涓殑 test_code_4 璇彞鐨勬敞閲娿?br /> 鐩稿簲杈撳嚭緇撴灉鍙樹負錛?br /> #-----------------------------------------
begin leak test...
ref count0:a=2 b=3 # 娉細姝ゅ杈撳嚭緇撴灉瑙嗘儏鍐靛彉鍖?
_a is invalid!
_b is invalid!
begin collect...
unreachable object num:0
garbage object num:0
#-----------------------------------------
緇撹錛歅ython 鐨?gc 鏈夋瘮杈冨己鐨勫姛鑳斤紝姣斿璁劇疆 gc.set_debug(gc.DEBUG_LEAK) 灝卞彲浠ヨ繘琛屽驚鐜紩鐢ㄥ鑷寸殑鍐呭瓨娉勯湶鐨勬鏌ャ傚鏋滃湪寮鍙戞椂榪涜鍐呭瓨娉勯湶媯鏌ワ紱鍦ㄥ彂甯冩椂鑳藉紜繚涓嶄細鍐呭瓨娉勯湶錛岄偅涔堝氨鍙互寤墮暱 Python 鐨勫瀮鍦懼洖鏀舵椂闂撮棿闅斻佺敋鑷充富鍔ㄥ叧闂瀮鍦懼洖鏀舵満鍒訛紝浠庤屾彁楂樿繍琛屾晥鐜囥?br />
]]>
for i in range ( 1000000 * 10 ):
del i
if ( __name__ == "__main__" ):
test()
while ( True ):
time.sleep( 1 )
瑙傚療mem:鍐呭瓨緇存寔涓嶅彉!
浠庤繖鐐瑰彲浠ョ寽嫻?python涓嶆槸绔嬪嵆閲婃斁璧勬簮鐨?
涓漢嫻嬭瘯浠ｇ爜:
-----------------------------------------------test0.py-------------------------------------
import time
def test():
for i in range ( 1000000 * 10 ):
del i
def test_2():
#i = range ( 1000000 * 10 )
#del i
pass
def test_3():
#i = "*" * ( 1000000 * 10 )
#del i
pass
if ( __name__ == "__main__" ):
for i in range( 10 ):
test()
test_2()
test_3()
time.sleep( 1 )
while ( True ):
time.sleep( 1 )
-----------------------------------------------------test0.py--------------------------------------
榪愯 python test0.py
"while ( True ):
time.sleep( 1 )
"
淇濊瘉python涓嶉鍑?
鍙戠幇python鐨勫唴瀛樺崰鐢ㄧ巼涓?0%.
濡備綍瑙ｅ喅榪欎釜闂鍛?鐪嬩笅闈㈢殑:
-----------------------------------------------test1.py-------------------------------------
#coding=utf-8
import time
max_number = 1000000 * 10
def test_0():
for i in range ( max_number ):
del i
def test_1():
for i in range( 1000 ):
for i in range ( max_number / 1000 ):
del i
if ( __name__ == "__main__" ):
#test_0()#鍐呭瓨浣跨敤鐜囧崰40%
test_1()#鍐呭瓨浣跨敤鐜囧崰0.2%
print "---------------------"
while ( True ):
time.sleep( 1 )
-----------------------------------------------test1.py-------------------------------------
鎴戞兂闂:闂涔熻瑙ｅ喅浜?
榪欏氨瑕佺湅浣犵殑瀹為檯闇姹傛槸浠涔堜簡.
渚嬪:
鎴戝仛榪囦竴涓埇铏▼搴?濡傛灉涓嶆柇寰榪欎釜綰跨▼閲岄潰浼犻抲rl,閭ｄ箞榪欎釜綰跨▼涓嶅埌涓浼氬氨鎸備簡.鎴戠殑鏀硅繘鏂規(guī)硶:灝辨槸鎺у埗榪欑嚎紼嬭兘澶熸帴鍙楃殑url闃熷垪闀垮害.浠ュ強鍏朵粬鐨勪紭鍖?
鍏跺疄榪欎釜涓嶆槸寰幆瀵艱嚧鐨勫唴瀛樿python鎸佹湁,鑰屾槸range( n )璁﹑ython鍒嗛厤浜嗗緢澶氱殑鍐呭瓨.閫鍑簍est(),python鍥炴敹鍐呭瓨,浣嗘槸python騫朵笉閲婃斁浜?鑰屾槸璁﹑ool鎸佹湁鍐呭瓨絀洪棿.
]]>
['a', 's', 'b']
>>>params.values()
['av', 'sv', 'bv']
>>>params.items()
[('a', 'av'), ('s', 'sv'), ('b', 'bv')]
>>>[k for k,v in params.items()]
['a', 's', 'b']
>>>[v for k,v in params.items()]
['av', 'sv', 'bv']
>>>["%s=%s" % (k,v) for k,v in params.items()]
['a=av', 's=sv', 'b=bv']
]]>
>>>li.extend(['c','d'])
>>>li
['a', 'b', 'c', 'd']
>>>li.append(['e','f'])
>>>li
['a', 'b', 'c', 'd',['e','f']]
2. 鎼滅儲 鎼滅儲 list
>>>li.index('b')
>>>li
1
3. List 榪愮畻絎︼紜 鍜?×
>>> li = ['a', 'b']>>> li = li + ['example', 'new'] >>> li['a', 'b', 'example', 'new']
>>> li += ['two'] >>> li['a', 'b', 'example', 'new', 'two']
>>> li = [1, 2] * 3 >>> li[1, 2, 1, 2, 1, 2]
4.浣曡皳 Python 涓殑 True
·0涓篺alse; 鍏跺畠鎵鏈夋暟鍊肩殕涓?true銆?br /> ·絀轟覆 ("") 涓篺alse; 鍏跺畠鎵鏈夊瓧絎︿覆鐨嗕負 true銆?br /> ·絀簂ist ([])涓篺alse; 鍏跺畠鎵鏈夊瓧絎︿覆鐨嗕負 true銆?br /> ·絀?tuple (()) 涓篺alse; 鍏跺畠鎵鏈夊瓧絎︿覆鐨嗕負 true銆?br /> ·絀?dictionary ({}) 涓篺alse; 鍏跺畠鎵鏈夊瓧絎︿覆鐨嗕負 true銆?
]]>