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Re: [O] Python Code Block error with header option :results output

From: Christian Moe
Subject: Re: [O] Python Code Block error with header option :results output
Date: Sat, 01 Feb 2014 07:56:01 +0100
User-agent: mu4e; emacs 24.3.1

Eric Schulte writes:

> Soapy Smith <address@hidden> 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."


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


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