010. Python的整形占多大内存?
示例代码
import sys
a = 0
print(a.__sizeof__()) # 24
print(sys.getsizeof(a)) # 24
- 所以答案是24？并不是！看下面
import sys
b = 1
print(b.__sizeof__()) # 28
print(sys.getsizeof(b)) # 28
- 变了
- 难道都会变？
import sys
c = 3
print(c.__sizeof__()) # 28
print(sys.getsizeof(c)) # 28
- 不是你想的那样的！
- 但的确是动态的
import sys
d = 1073741823
e = 1073741824
print(d.__sizeof__()) # 28
print(sys.getsizeof(e)) # 32
- 有点规律了，1073741824是什么鬼？它是2**30
- 实际上，python的int类型就是动态的，每230增加4个字节**
- 那下一个边界是？2**60！
print(sys.getsizeof(2**60)) # 36
- 那其他类型呢？可以参考附录
sizeof()
- 返回内存中的大小，单位字节
| __sizeof__(self, /)
| Returns size in memory, in bytes.
getsizeof()
- 这是sys模块的一个方法
- 在pycharm中你只能看到如下内容，不过大致也是返回对象的大小，单位是字节
def getsizeof(p_object, default): # real signature unknown; restored from __doc__
"""
getsizeof(object, default) -> int
Return the size of object in bytes.
"""
return 0
-
2个貌似一样
-
其实不然
b = [] print(b.__sizeof__()) # 40 print(sys.getsizeof(b)) # 56 不一样(我在jupyter中执行的结果) # 如果你在pycharm中执行可能此处是 64
import sys
l = []
w =[1, 2]
x =[4, 5, 7, 9]
y =[2, 8, 6, 56, 45, 89, 88]
print('sizeof:%d,getsize:%d' %(l.__sizeof__(),sys.getsizeof(l)))
print('sizeof:%d,getsize:%d' %(w.__sizeof__(),sys.getsizeof(w)))
print('sizeof:%d,getsize:%d' %(x.__sizeof__(),sys.getsizeof(x)))
# sizeof:40,getsize:64 # 此处就是在pycharm中执行的
# sizeof:56,getsize:80
# sizeof:72,getsize:96
-
getsizeof() 方法调用
__sizeof__方法，但同时会附带一些额外的GC操作(arbage collector overhead). 因此前者的大小比后者要大一些 -
列表初始化的时候是40，每加一个元素是8个字节
-
代码大了之后，内存管理就显得非常重要了，现在仅作了解
附录
https://stackoverflow.com/questions/449560/how-do-i-determine-the-size-of-an-object-in-python
-
对于其他类型，有人做了一些测试
-
基于 64-bit Python 3.6，使用Anaconda
Empty Bytes type scaling notes 28 int +4 bytes about every 30 powers of 2 37 bytes +1 byte per additional byte 49 str +1-4 per additional character (depending on max width) 48 tuple +8 per additional item 64 list +8 for each additional 224 set 5th increases to 736; 21nd, 2272; 85th, 8416; 341, 32992 240 dict 6th increases to 368; 22nd, 1184; 43rd, 2280; 86th, 4704; 171st, 9320 136 func def does not include default args and other attrs 1056 class def no slots 56 class inst has a __dict__ attr, same scaling as dict above 888 class def with slots 16 __slots__ seems to store in mutable tuple-like structure first slot grows to 48, and so on.