From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christian Moe <mail@christianmoe.com>
Subject: Re: Python Code Block error with header option :results output
Date: Sat, 01 Feb 2014 07:56:01 +0100
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To: Eric Schulte <schulte.eric@gmail.com>
Cc: Soapy Smith <soapy-smith@comcast.net>, emacs-orgmode@gnu.org


Eric Schulte writes:

> Soapy Smith <soapy-smith@comcast.net> writes:
>
>> Hello-
>>
>> I am not a user of Python (yet).  During a comparison of code block
>> behavior between Clojure and Python, I discovered a possible Python
>> error.
>>
>> Here is the code block:
>>
>> #+begin_src python :results output
>>  a = (1, 2, 3, 4)
>>  return a
>> #+end_src
>>
>> The evaluation of this block results in this error:
>>
>>   File "<stdin>", line 2
>> SyntaxError: 'return' outside function
>>
>> Could someone please comment if this is expected Python behavior?
>>
>
> You should only use "return" like that in a python code block when you
> have ":results value".

To expand briefly on that (since this can be perplexing): 

The need to use `return' at all when returning the value is a special
quirk of Python code blocks, and does not apply to (any?) other languages.

As explained on Worg, with `:results value' (the default), 

"Internally, the value is obtained by wrapping the code in a function
definition in the external language, and evaluating that
function. Therefore, code should be written as if it were the body of
such a function. In particular, note that Python does not automatically
return a value from a function unless a return statement is present, and
so a ‘return’ statement will usually be required in Python."

http://orgmode.org/manual/Results-of-evaluation.html

So when using `:results output', using `return' causes an error
because there is no function to return anything from.

Yours,
Christian