Python in emacs: __name__ == '__main__', but somehow not

Question

I am coding python in emacs. However, somehow the python interpreter running in emacs manages to surprise me.

If I write

print()
print(__name__)
print(__name__=='__main__')
if __name__ == '__main__':
    print("indeed")

in an emacs buffer, and tell emacs to start an interpreter and run the content of this buffer, I get a buffer containing

Python 3.3.5 (default, Mar 18 2014, 02:00:02) 
[GCC 4.2.1 20070831 patched [FreeBSD]] on freebsd9
Type "help", "copyright", "credits" or "license" for more information.
>>> 
__main__
True
>>> 

(Both __main__ and True are the outputs from the print statement; the python buffer always displays the >>> and prints immediately after it. I am aware of this, this is not a problem.)

From the command line, both python and python -i show the 'indeed', as expected.

How is Emacs able to the inconsistency of evaluating __name__=='__main__' to True, while not executing things inside if __name__ == '__main__':? And how do reconfigure it so it does not do so any more?

Answer 1

As @Wooble mentioned in the comment, it might be python.el issue: C-c C-c runs
python-shell-send-buffer function:

python-shell-send-buffer is an interactive compiled Lisp function in `python.el'.

(python-shell-send-buffer &optional ARG)

Send the entire buffer to inferior Python process. With prefix ARG allow execution of code inside blocks delimited by "if __name__=='__main__':"

i.e., to print "indeed", add prefix C-u C-c C-c.

Q: I have tried to dig through python.el, and I am still not sure how and where it does this. Can you explain, so I can modify the default behaviour?

To find out what C-c C-c does in your case open a python file and type M-x describe-key RET followed by C-c C-c (actually press the keys). By default it runs python-shell-send-buffer function in python.el. You could redefine the keys to call the function with an argument so that C-c C-c would behave like C-u C-c C-c that enables running "if __name__=='__main__':" part:

;; Make C-c C-c behave like C-u C-c C-c in Python mode
(require 'python)
(define-key python-mode-map (kbd "C-c C-c")
  (lambda () (interactive) (python-shell-send-buffer t)))

Answer 2

This 'Feature' gets never old. Try using

__name__=='__main__':

without the whitespace between the opperator.

Then python.el will not bypass it. So look at your code formater.

Answer 3

Once you have started the python shell, you can simply override the variable:

__name__ = 'repl' 

This prevents any if __name__=='__main__': blocks from running on any subsequent C-c C-c invocations.