python中如何查看指定内存地址的内容

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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。

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。

对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。

i = 100
type(i)
# int
s = string_at(id(i), getsizeof(i))
type(s)
# bytes
s
# b'>x00x00x00x00x00x00x00xa0x99xfdx1dx00x00x00x00x01x00x00x00x00x00x00x00dx00x00x00'
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。

>>> 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

但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