python memory del list [:] vs list = []

Question

在python我注意到,如果你这样做

mylist = []

for i in range(0,100000000):
    mylist.append('something here to take memory')

mylist = []

这似乎是第二次通话

mylist = []

将删除引用,它将被收集,但是,因为我看着它们没有.

我用的时候

del mylist[:]

它几乎删除了除了几个megs之外的所有内容(只是查看过程)

我用的时候

del mylist[:]
gc.collect()

我似乎在创建列表之前返回相同数量的内存

所以....为什么呢

mylist = []

不行？？？据我所知,没有别的东西能引用它

Answer 1

你是如何衡量的？

我做了一个小测试,但没有确认你的结果.这是来源:

import meminfo, gc, commands

page_size = int(commands.getoutput("getconf PAGESIZE"))

def stat(message):
    s = meminfo.proc_stat()
    print "My memory usage %s: RSS: %dkb, VSIZE: %dkb" % (
        message, s['rss']*page_size/1024, s['vsize']/1024)
mylist = []

stat("before allocating a big list")
for i in range(0,3000000):
    mylist.append('something here to take memory')

stat("after allocating big list")
### uncomment one of these:
mylist = []
# del mylist[:]
stat("after dropping a big list")
gc.collect()
stat("after gc.collect()")
gc.collect()
stat("after second gc.collect()")
gc.collect()
stat("after third gc.collect()")

使用的meminfo模块位于:http://gist.github.com/276090

这些是mylist = []的结果:

My memory usage before allocating a big list: RSS: 3396kb, VSIZE: 7324kb
My memory usage after allocating big list: RSS: 50700kb, VSIZE: 55084kb
My memory usage after dropping a big list: RSS: 38980kb, VSIZE: 42824kb
My memory usage after gc.collect(): RSS: 38980kb, VSIZE: 42824kb
My memory usage after second gc.collect(): RSS: 38980kb, VSIZE: 42824kb
My memory usage after third gc.collect(): RSS: 38980kb, VSIZE: 42824kb

这是del mylist [:]的结果:

My memory usage before allocating a big list: RSS: 3392kb, VSIZE: 7324kb
My memory usage after allocating big list: RSS: 50696kb, VSIZE: 55084kb
My memory usage after dropping a big list: RSS: 38976kb, VSIZE: 42824kb
My memory usage after gc.collect(): RSS: 38976kb, VSIZE: 42824kb
My memory usage after second gc.collect(): RSS: 38976kb, VSIZE: 42824kb
My memory usage after third gc.collect(): RSS: 38976kb, VSIZE: 42824kb

Python可以为自己的堆分配内存,但它不一定在垃圾收集后立即释放它.