Python Forum

the documentation for exec() says the first argument must be a string or code object and that only the unix style end-of-line is accept. but i have found that it also works with bytes and works with both '\r\n' and '\r' style end of lines.

anyone know why?

Skaperen Wrote:the documentation for exec() says the first argument must be a string or code object and that only the unix style end-of-line is accept

Do you have a link to this part of the documentation?

no. it's in a PDF. what does your documentation say?

From python.org:

Quote:This function supports dynamic execution of Python code. object must be either a string or a code object. If it is a string, the string is parsed as a suite of Python statements which is then executed (unless a syntax error occurs).

/.../

Note that the parser only accepts the Unix-style end of line convention. If you are reading the code from a file, make sure to use newline conversion mode to convert Windows or Mac-style newlines.

Oh I see, I missed the footnote. Well, Skaperen, can you send us an MCVE where it works unexpectedly with Windows or Mac end of lines?

MCVE? i don't know what that means.

here is a simple demo:

Output:
lt2a/forums /home/forums 45> py3
Python 3.6.8 (default, Jan 14 2019, 11:02:34) 
[GCC 8.0.1 20180414 (experimental) [trunk revision 259383]] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> a='print(repr((a,b,c,d,e,f)))\n'
>>> b='print(repr((a,b,c,d,e,f)))\r'
>>> c='print(repr((a,b,c,d,e,f)))\r\n'
>>> d=b'print(repr((a,b,c,d,e,f)))\n'
>>> e=b'print(repr((a,b,c,d,e,f)))\r'
>>> f=b'print(repr((a,b,c,d,e,f)))\r\n'
>>> exec(a)
('print(repr((a,b,c,d,e,f)))\n', 'print(repr((a,b,c,d,e,f)))\r', 'print(repr((a,b,c,d,e,f)))\r\n', b'print(repr((a,b,c,d,e,f)))\n', b'print(repr((a,b,c,d,e,f)))\r', b'print(repr((a,b,c,d,e,f)))\r\n')
>>> exec(b)
('print(repr((a,b,c,d,e,f)))\n', 'print(repr((a,b,c,d,e,f)))\r', 'print(repr((a,b,c,d,e,f)))\r\n', b'print(repr((a,b,c,d,e,f)))\n', b'print(repr((a,b,c,d,e,f)))\r', b'print(repr((a,b,c,d,e,f)))\r\n')
>>> exec(c)
('print(repr((a,b,c,d,e,f)))\n', 'print(repr((a,b,c,d,e,f)))\r', 'print(repr((a,b,c,d,e,f)))\r\n', b'print(repr((a,b,c,d,e,f)))\n', b'print(repr((a,b,c,d,e,f)))\r', b'print(repr((a,b,c,d,e,f)))\r\n')
>>> exec(d)
('print(repr((a,b,c,d,e,f)))\n', 'print(repr((a,b,c,d,e,f)))\r', 'print(repr((a,b,c,d,e,f)))\r\n', b'print(repr((a,b,c,d,e,f)))\n', b'print(repr((a,b,c,d,e,f)))\r', b'print(repr((a,b,c,d,e,f)))\r\n')
>>> exec(e)
('print(repr((a,b,c,d,e,f)))\n', 'print(repr((a,b,c,d,e,f)))\r', 'print(repr((a,b,c,d,e,f)))\r\n', b'print(repr((a,b,c,d,e,f)))\n', b'print(repr((a,b,c,d,e,f)))\r', b'print(repr((a,b,c,d,e,f)))\r\n')
>>> exec(f)
('print(repr((a,b,c,d,e,f)))\n', 'print(repr((a,b,c,d,e,f)))\r', 'print(repr((a,b,c,d,e,f)))\r\n', b'print(repr((a,b,c,d,e,f)))\n', b'print(repr((a,b,c,d,e,f)))\r', b'print(repr((a,b,c,d,e,f)))\r\n')
>>>

My idea is that the footnote is obsolete. You may have discovered a flaw in the official documentation. Now I think it's not our job to find an example of the footnote's claim. It should be included in the documentation.

i discovered this because i wanted to see what exception it would actually raise. but the fact that it can just do these things lets me simplify my code. i don't need to decode bytes to strings and i don't need to do '\n'.join(whatever.splitlines()) to be sure i have consistent line endings for code snippets to run in exec().

(Jul-27-2019, 10:56 PM)Skaperen Wrote: [ -> ]MCVE? i don't know what that means.

mcve = a minimal, complete and verifiable example
https://stackoverflow.com/help/minimal-r...le-example

i knew those words, just not the acronym.