What is a bytes-like object

Question

In Python 3.6, the base64.b64encode() function requires "a bytes-like object, not str".

What is an example of a bytes-like object as opposed to a normal string?

Answer 1

Anything that logically stores a sequence of bytes qualifies. That includes the actual bytes type, bytearray, mmap.mmap, array.array('B'), etc. str in Python 3 is a text type; the characters aren't stored in a specified encoding, so you can't use them as raw binary data directly; they must be encode-ed explicitly with a specific encoding.

For the technical definition, see the Python 3 glossary:

An object that supports the Buffer Protocol and can export a C-contiguous buffer. This includes all bytes, bytearray, and array.array objects, as well as many common memoryview objects. Bytes-like objects can be used for various operations that work with binary data; these include compression, saving to a binary file, and sending over a socket.

Some operations need the binary data to be mutable. The documentation often refers to these as "read-write bytes-like objects". Example mutable buffer objects include bytearray and a memoryview of a bytearray. Other operations require the binary data to be stored in immutable objects ("read-only bytes-like objects"); examples of these include bytes and a memoryview of a bytes object.

• Yaroslav Surzhikov: It is worth mentioning that the string could be converted to bytes
• ShadowRanger: @YaroslavSurzhikov: Added a note on that.
• Max: @ShadowRanger So, for example, if I was to use a json string in base64.b64encode(), how would I change the string to a bytes-like object?
• ShadowRanger: @RayAntebioni: Typically JSON is represented as UTF-8, so you'd pass jsonstring.encode('utf-8').