bytes
contents
related file
- cpython/Objects/bytesobject.c
- cpython/Include/bytesobject.h
- cpython/Objects/clinic/bytesobject.c.h
memory layout
The memory layout of PyBytesObject looks like memory layout of tuple object and memory layout of int object, but simpler than any of them.
example
empty bytes
bytes object is an immutable object, whenever you need to modify a bytes object, you need to create a new one, which keeps the implementation simple.
s = b""
ascii characters
Let’s initialize a bytes object with ASCII characters
s = b"abcdefg123"
nonascii characters
s = "我是帅哥".encode("utf8")
summary
ob_shash
The field ob_shash should store the hash value of the byte object, value -1 means not computed yet.
The first time the hash value is computed, it will be cached in the ob_shash field.
The cached hash value can save recalculation and speed up dictionary lookups
ob_size
The field ob_size is inside every PyVarObject. PyBytesObject uses this field to store size information to keep O(1) time complexity for the len() operation and to track the size of non-ASCII strings (which may contain null characters inside)
summary
The PyBytesObject is a Python wrapper of C-style null-terminated strings, with ob_shash for caching the hash value and ob_size for storing size information
The implementation of PyBytesObject looks like the embstr encoding in redis
```shell script redis-cli 127.0.0.1:6379> set a “hello” OK 127.0.0.1:6379> object encoding a “embstr”
```