bug#39070: python interpreter within Emacs fails on simple test (syntax error)

bug#39070: python interpreter within Emacs fails on simple test (syntax error)

[Pierre ALBARÈDE]

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This small program

mac2011% cat bug.py
print(__name__ == "__main__")
#if True:
if __name__ == "__main__":
     print("main")
else:
     print("not main")

works well in Terminal :

mac2011% python bug.py
True
main

mac2011% python --version
Python 3.6.9 :: Anaconda, Inc.

but it does not work in Emacs python mode :

mac2011% Emacs -Q bug.py

(version)
"GNU Emacs 28.0.50 (build 1, x86_64-apple-darwin15.6.0, NS appkit-1404.47 
Version 10.11.6 (Build 15G22010))
  of 2020-01-09"

Files opens in (Python ElDoc) mode

Python menu

Start interpreter (C-c C-p)

Eval buffer (C-c C-c)

Python 3.6.9 |Anaconda, Inc.| (default,     Jul 30 2019, 13:42:17)
[GCC 4.2.1 Compatible Clang 4.0.1 (tags/RELEASE_401/final)] on darwin
Type "help", "copyright", "credits" or     "license" for more information.
 >>> python.el: native completion setup loaded
 >>> Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   File "/Users/alba/Documents/projets/plot time series/bug.py", line 5
     else:
        ^
SyntaxError: invalid syntax
 >>>

Replacing 'if __name__ == "__main__":' by 'if True:', there is no more error.

Replacing "__main__" by "__main_", there is no more error.

Same with Python 3.7.6.

'print("main") if __name__ == '__main__' else  print("not main")' works.

Best regards.

-- 
Pierre ALBARÈDE




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bug#39070: python interpreter within Emacs fails on simple test (syntax error)

[Federico Tedin]

> Replacing 'if __name__ == "__main__":' by 'if True:', there is no more error.
>
> Replacing "__main__" by "__main_", there is no more error.
>
> Same with Python 3.7.6.
>
> 'print("main") if __name__ == '__main__' else  print("not main")' works.
>
> Best regards.

Hello Pierre,

This behavior is due to `python-shell-send-buffer's SEND-MAIN
argument:

"When optional argument SEND-MAIN is non-nil, allow execution of
code inside blocks delimited by "if __name__== '__main__'" "

So when this argument is nil (the default), the whole block under "if
__name__== '__main__'" " will be removed (along the line containing the
"if" itself).
Your example breaks because you added an "else:" to your "if", so when
Emacs removes that part, a syntax error is raised.

Try the following test file:

print("1")

if __name__ == "__main__":
    print("2")

print("3")

Using C-c C-c on it should yield "1 3", but using C-u C-c C-c
(i.e. SEND-MAIN set to t) should yield "1 2 3".

Hope that helps.
- Fede

bug#39070: python interpreter within Emacs fails on simple test (syntax error)

[Lars Ingebrigtsen]

Federico Tedin <federicotedin@gmail.com> writes:

> Using C-c C-c on it should yield "1 3", but using C-u C-c C-c
> (i.e. SEND-MAIN set to t) should yield "1 2 3".

So I guess this works as designed, and I'm closing this bug report.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no