RFE: uuid.UUID(bytes=...): support bytes-like types, not only bytes

[jnwatson]

BPO	29729
Nosy	@warsaw, @vstinner, @serhiy-storchaka, @jnwatson
PRs	bpo-29729: uuid.UUID now accepts bytes-like object #3801

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-03-05.19:59:58.391>
labels = ['3.7', 'type-feature', 'library']
title = 'RFE: uuid.UUID(bytes=...): support bytes-like types, not only bytes'
updated_at = <Date 2017-09-28.20:43:09.315>
user = 'https://github.com/jnwatson'

bugs.python.org fields:

activity = <Date 2017-09-28.20:43:09.315>
actor = 'vstinner'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2017-03-05.19:59:58.391>
creator = 'jnwatson'
dependencies = []
files = []
hgrepos = []
issue_num = 29729
keywords = ['patch']
message_count = 8.0
messages = ['289045', '303242', '303246', '303248', '303250', '303277', '303278', '303279']
nosy_count = 4.0
nosy_names = ['barry', 'vstinner', 'serhiy.storchaka', 'jnwatson']
pr_nums = ['3801']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue29729'
versions = ['Python 3.7']

[jnwatson]

The assertion:

File "/usr/lib/python3.6/uuid.py", line 150, in __init__
assert isinstance(bytes, bytes_), repr(bytes)

is too specific (and IMHO, unpythonic). One may want to pass a bytearray or a memoryview. See int.from_bytes for an example that takes "bytes" but accepts anything that acts like a bytes.

A simple solution may be to delete the assertion (it worked for me).

Example code:

import uuid

b = uuid.uuid1().bytes
ba = bytearray(b)
print(uuid.UUID(bytes=b))

# another API that works similarly, accepts a bytearray
print(int.from_bytes(ba, byteorder='big'))

# fails on assertion
print(uuid.UUID(bytes=ba))

[serhiy-storchaka]

I agree. In any case assert is a bad way of checking argument types. It was
added in 65b6a80 as a part of migration to
Python 3. I guess for debugging purposes. Now it isn't needed,
int.from_bytes() checks whether the type is appropriate.

Do you want to create a pull request Nic?

[serhiy-storchaka]

Ah, Victor already have created a PR!

[vstinner]

Serhiy: is it safe to accept any memoryview? Or should we call explicitly .cast('B') on memory views to prevent bad surprises?

The asyncio module doesn't do anything special in sock_sendall(). "data" is passed directly to socket.send(), unchanged.

So maybe it's just fine to not do anything special.

[serhiy-storchaka]

The code doesn't work nice with general objects supporting the buffer protocol. The length check suppose that the value has a length, and it is the size in bytes. The code for bytes_le suppose that the value supports slicing and concatenating results of the slicing. And all this code is made as fast as possible. Additional checks and conversions will slowdown it.

[vstinner]

The code doesn't work nice with general objects supporting the buffer protocol. The length check suppose that the value has a length, and it is the size in bytes. The code for bytes_le suppose that the value supports slicing and concatenating results of the slicing. And all this code is made as fast as possible. Additional checks and conversions will slowdown it.

I enhanced my PR to also accept memoryview and bytearray in bytes_le. I don't think that performance matters so much here. First we need correctness, accept any bytes-like objects, no?

[serhiy-storchaka]

I have tested, this doesn't affect performance.