python中如何查看指定内存地址的内容

python中一般并不需要查看内存内容,但作为从C/C++过来的人,有的时候还是想看看内存,有时是为了验证内容是否与预期一致,有时是为了探究下内存布局。

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from sys import getsizeof 
from ctypes import string_at

'''
getsizeof(...)
getsizeof(object, default) -> int
Return the size of object in bytes.

string_at(ptr, size=-1)
string_at(addr[, size]) -> string
Return the string at addr.
'''

getsizeof用于获取对象占用的内存大小,string_at用于获取指定地址、指定字节长度的内容,因为返回的对象类型是bytes,可以调用hex()函数转换成16进制查看。

int对象的内存内容如下,首先通过函数id获取对象的内存地址。

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i = 100
type(i)
# int
s = string_at(id(i), getsizeof(i))
type(s)
# bytes
s
# b'>\x00\x00\x00\x00\x00\x00\x00\xa0\x99\xfd\x1d\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00d\x00\x00\x00'
s.hex()
# '3e00000000000000a099fd1d00000000010000000000000064000000'

如果对int对象的内存布局不熟悉,可能看不出什么。

再举一个numpy的例子。

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>>> import numpy as np
>>> a = np.arange(12).reshape(3,4)
>>> a
array([[ 0, 1, 2, 3],
[ 4, 5, 6, 7],
[ 8, 9, 10, 11]])

>>> a.data
<memory at 0x00000000062483A8>
>>> m = a.data
>>> type(m)
memoryview
>>> m.hex()
'000000000100000002000000030000000400000005000000060000000700000008000000090000000a0000000b000000'

>>> a.ctypes.data
68393696
>>> string_at(a.ctypes.data, a.nbytes).hex()
'000000000100000002000000030000000400000005000000060000000700000008000000090000000a0000000b000000'

上面展示的两个例子,一个是通过memoryview对象查看,另一个是通过string_at查看。不是所有对象都支持memoryview

class memoryview(obj)

Create a memoryview that references obj. obj must support the buffer protocol. Built-in objects that support the buffer protocol include bytes and bytearray.

—— from https://docs.python.org/3/library/stdtypes.html#memoryview

string_at

ctypes.string_at(address, size=-1)

This function returns the C string starting at memory address address as a bytes object. If size is specified, it is used as size, otherwise the string is assumed to be zero-terminated.

—— from https://docs.python.org/3/library/ctypes.html?highlight=string_at#ctypes.string_at

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