What's the relationship between str and bytes in python?

Question

Consider the following typescript:

>>> s = 'a'
>>> isinstance(s, bytes)
True
>>> isinstance(s, str)
True
>>> isinstance(s, unicode)
False
>>> isinstance(s.decode('utf-8'), unicode)
True

How come s is both a str and a bytes? Is one of those a descendant of the other one?

How did I run into it? I was trying to find description of decode method in the docs. I couldn't find it for str, but was able for bytes.

Added the Python 2.x tag, as this seems only to be the case in Python 2. Also, `bytes == str` yields `True` in Python 2.7 — tobias_k, Nov 17 '16 at 15:19
Indeed. I mainly deal with Python 3, so I instinctively looked in that part of the documentation. — x-yuri, Nov 17 '16 at 15:31

score 4 · Accepted Answer · answered Nov 17 '16 at 15:20

You are looking at the wrong documentation.

This equivalence is only true in Python 2.7. There, bytes was introduced as an alias to str in order to ease migration to Python 3.

In Python 3, str is what was previously called unicode, bytes is the type that was previously called str.

The documentation for str.decode for Python 2 is here.

What's the relationship between str and bytes in python?

1 Answers1