str 和 bytes

In [8]: b=b'hello'

In [9]: type(b)
Out[9]: builtins.bytes

In [10]: s='hello'

In [11]: type(s)
Out[11]: builtins.str

To convert from str to bytes, use str.encode().:

In [12]: a=str.encode(s)

In [13]: type(a)
Out[13]: builtins.bytes

To convert from bytes to str, use bytes.decode():

In [14]: c=bytes.decode(a)

In [15]: type(c)
Out[15]: builtins.str