Is the documentation for the bytes consdtructor wrong? (original) (raw)

February 9, 2025, 9:39pm 1

The built-in bytes built-in function (class constructor) is shown here:
functions.html#func-bytes
as

class bytes(source=b'')
class bytes(source, encoding)
class bytes(source, encoding, errors)

and here:
stdtypes.html#bytes
as
*class* bytes([*source* [, *encoding* [, *errors* ]]])

This shows to me that the encoding is not needed.
But if I try:
>>> bytes('abc')
I get
TypeError: string argument without an encoding

(Side note: b'abc' works fine, with any ASCII characters)
(Side note: an empty bytes constructor bytes() works fine)

Is the documentation wrong, or am I missing something?

smontanaro (Skip Montanaro) February 9, 2025, 10:28pm 2

Note that the single argument call requires a bytes object. If you pass a string object, you have to provide the encoding argument. I’m not sure if it’s completely clear in the page you referenced. If not, you could submit a bug report.

PeterL (Peter Lovett) February 9, 2025, 10:46pm 3

Oh, I see. I guess that’s implied by the source=b'' line, but it wasn’t clear to me. I don’t know if that could be made clear in the signature. Probably needs a comment like you just said: “the single argument call requires a bytes object.”

Stefan2 (Stefan) February 10, 2025, 2:04am 4

Not true, try bytes([1,2,3]) or bytes(3).

Stefan2 (Stefan) February 10, 2025, 2:09am 5

The doc says “constructor arguments are interpreted as for bytearray()” and the doc for that is directly above and says about source: 'If it is a string, you must also give the encoding".

Stefan2 (Stefan) February 10, 2025, 2:40am 6

Though I think that that bytearray() link should be changed to go to that function instead of to the stdtypes page.

smontanaro (Skip Montanaro) February 10, 2025, 3:05am 7

True, since bytes objects are really immutable arrays of ints. I fooled myself looking at OP’s three examples where the first one explicitly showed a zero-length bytes literal as the argument. That kind of masked the nature of the argument’s type. (I don’t use bytes objects much.)