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bytes.fromhex() should parse a bytes #129349
Description
Feature or enhancement
Proposal:
bytes.fromhex() should accept a bytes:
>>> bytes.fromhex(b'8a3218def90a84cb4373beed87d9ba1ccc7d90d1')
b'\x8a2\x18\xde\xf9\n\x84\xcbCs\xbe\xed\x87\xd9\xba\x1c\xcc}\x90\xd1'Background:
bytes.fromhex() accepts a str:
>>> bytes.fromhex('8a3218def90a84cb4373beed87d9ba1ccc7d90d1')
b'\x8a2\x18\xde\xf9\n\x84\xcbCs\xbe\xed\x87\xd9\xba\x1c\xcc}\x90\xd1'However, it refuses to parse a byte string:
>>> bytes.fromhex(b'8a3218def90a84cb4373beed87d9ba1ccc7d90d1')
Traceback (most recent call last):
File "<python-input-0>", line 1, in <module>
bytes.fromhex(b'8a3218def90a84cb4373beed87d9ba1ccc7d90d1')
~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: fromhex() argument must be str, not bytesThis requires an extra .decode(), which is rather wasteful given that the str is not of any real use.
This came up for me in parsing the output of git cat-file --batch, which must be a binary stream because it contains bytes, but includes header lines like
8a3218def90a84cb4373beed87d9ba1ccc7d90d1 100644 1394
The integers are parseable directly from bytes:
>>> int(b'100644', 8)
33188so it seems like an omission that the SHAs are not.
Has this already been discussed elsewhere?
This is a minor feature, which does not need previous discussion elsewhere
Links to previous discussion of this feature:
No response
Linked PRs
Reacted by Geoffrey Thomas
Activity
Accept bytes in bytes.fromhex()/bytearray.fromhex()
serhiy-storchaka commentedon Feb 20, 2025
You have to look at the discussion that preceded introduction of
bytes.fromhex()or ask the authors of the feature why it only supports str.BTW,
float.fromhex()also only supports str.serhiy-storchaka commentedon Feb 27, 2025
For reference,
bytes.fromhex()was added by @birkenfeld in 0b9b9e0.bytesat that time was a mutable type, later it was renamed tobytearray, andstrbecame newbytes. Initially,fromhex()accepted 8-bit and Unicode strings. It stopped support of 8-bit strings only after making newbytesand newstrnot interoperable in Python 3.0. So I do not see reasons against supportingbyteshere.Accept bytes in bytes.fromhex()/bytearray.fromhex()
Accept bytes in bytes.fromhex()/bytearray.fromhex()
Accept bytes in bytes.fromhex()/bytearray.fromhex()
gh-129349: Accept bytes in bytes.fromhex()/bytearray.fromhex() (#129844)
vstinner commentedon Mar 12, 2025
Implemented in e0637ce.
serhiy-storchaka commentedon Mar 13, 2025
I had doubts about supporting the general buffer protocol (see #779 and #71759). The buffer protocol is for binary data, and here we have text data. But it is difficult to decide in which cases to support only
bytes, in whichbytesandbytearray, and in which any "bytes-like" object.Note also that the
complexconstructor only supportsstr, notbytes(there may be open or closed issue for this).vstinner commentedon Mar 13, 2025
IMO it's convenient to accept bytes when the "text" is ASCII only.