| msg306521 - (view) |
Author: Arno-Can Uestuensoez (acue) |
Date: 2017-11-20 01:26 |
| Hello, I am currently writing some dual-version libraries and have to deal with str/unicode. The attached code example contains the str/unicode handling. The Python3.6.2 release behaves as I did not expected for all of the following the conversions: unicode = str # @ReservedAssignment # it is intentional mystring = "abc" u0 = unicode(bytes(mystring.encode())) # == str(mystring) mystring = "abc" u0 = unicode(bytes(mystring.encode('utf-8'))) # == str(mystring) mystring = "abc" u0 = unicode(bytes(mystring.encode('ascii'))) # == str(mystring) mystring = b"abc" u0 = unicode(mystring) # == str(mystring) results for Python3 in: type: <class 'str'> len: 6 b'abc' while in Python2: type: <type 'unicode'> len: 3 abc I am not sure whether this is the intended behavior because the manual could eventually be misinterpreted: 4.8.1. Bytes Objects Bytes objects are immutable sequences of single bytes. Since many major binary protocols are based on the ASCII text encoding, bytes objects offer several methods that are only valid when working with ASCII compatible data and are closely related to string objects in a variety of other ways. class bytes([source[, encoding[, errors]]]) Firstly, the syntax for bytes literals is largely the same as that for string literals, except that a b prefix is added: I expected the 'b'-prefix to be added to the input only, but I expect the output without a type-prefix, because it is just an attribute/property. The result for Python3 should be similar to Python2: type: <type 'str'> len: 3 abc Regards Arno |
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| msg306527 - (view) |
Author: Arno-Can Uestuensoez (acue) |
Date: 2017-11-20 05:37 |
| Hello, the following reduced example probably shows the issue a little better. I have currently not yet the 3.7+ environment, but guess the same behavior. Regards Arno |
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| msg306528 - (view) |
Author: Arno-Can Uestuensoez (acue) |
Date: 2017-11-20 05:46 |
| Sorry for the typo. |
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| msg306567 - (view) |
Author: STINNER Victor (vstinner) *  |
Date: 2017-11-20 17:09 |
| Calling str(bytes) is wrong in Python 3: $ python3 -bb Python 3.6.2 (default, Oct 2 2017, 16:51:32) >>> str(b'abc') BytesWarning: str() on a bytes instance Just don't do that :-) Use repr(bytes) if you want the b'...' format: >>> repr(b'abc') "b'abc'" |
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| msg306617 - (view) |
Author: Arno-Can Uestuensoez (acue) |
Date: 2017-11-21 02:54 |
| I got your point, missed it before, sorry. So just for completeness. My issue was basically about the ambiguity of the str()-constructor and the str()-built-in-function. Therefore the len/type prints. It works with parameters: (3.6.2) [acue@lap001 Desktop]$ python -bb Python 3.6.2 (default, Jul 29 2017, 14:24:56) [GCC 4.8.3 20140911 (Red Hat 4.8.3-7)] on linux Type "help", "copyright", "credits" or "license" for more information. >>> >>> str(b"abc") Traceback (most recent call last): File "", line 1, in BytesWarning: str() on a bytes instance >>> >>> >>> str(b"abc", "utf-8") 'abc' >>> >>> type(str(b"abc",'utf-8')) <class 'str'> >>> Is there a common approach to force the use of the str()-constructor instead of the str()-built-in function and/or the __str__()-method? This would make the shared code of Python2/Python3 much easier, at least for unicode()->str(). |
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| msg306622 - (view) |
Author: STINNER Victor (vstinner) * |
Date: 2017-11-21 03:05 |
| I'm sorry but the bug tracker is not the right place to ask such question. There are plenty of resources on the Internet explaining how to write code compatible with Python 2 and Python 3. |
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