Info Catalog org: Header arguments org: Working With Source Code org: Noweb reference syntax

org: Results of evaluation

 
 14.9 Results of evaluation
 ==========================
 
 The way in which results are handled depends on whether a session is
 invoked, as well as on whether ‘:results value’ or ‘:results output’ is
 used.  The following table shows the table possibilities.  For a full
 listing of the possible results header arguments see results.
 
                     Non-session              Session
 ‘:results value’    value of last            value of last expression
                     expression
 ‘:results output’   contents of STDOUT       concatenation of interpreter
                                              output
 
    Note: With ‘:results value’, the result in both ‘:session’ and
 non-session is returned to Org mode as a table (a one- or
 two-dimensional vector of strings or numbers) when appropriate.
 
 14.9.1 Non-session
 ------------------
 
 14.9.1.1 ‘:results value’
 .........................
 
 This is 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.
 
    This is the only one of the four evaluation contexts in which the
 code is automatically wrapped in a function definition.
 
 14.9.1.2 ‘:results output’
 ..........................
 
 The code is passed to the interpreter as an external process, and the
 contents of the standard output stream are returned as text.  (In
 certain languages this also contains the error output stream; this is an
 area for future work.)
 
 14.9.2 Session
 --------------
 
 14.9.2.1 ‘:results value’
 .........................
 
 The code is passed to an interpreter running as an interactive Emacs
 inferior process.  Only languages which provide tools for interactive
 evaluation of code have session support, so some language (e.g., C and
 ditaa) do not support the ‘:session’ header argument, and in other
 languages (e.g., Python and Haskell) which have limitations on the code
 which may be entered into interactive sessions, those limitations apply
 to the code in code blocks using the ‘:session’ header argument as well.
 
    Unless the ‘:results output’ option is supplied (see below) the
 result returned is the result of the last evaluation performed by the
 interpreter.  (This is obtained in a language-specific manner: the value
 of the variable ‘_’ in Python and Ruby, and the value of ‘.Last.value’
 in R).
 
 14.9.2.2 ‘:results output’
 ..........................
 
 The code is passed to the interpreter running as an interactive Emacs
 inferior process.  The result returned is the concatenation of the
 sequence of (text) output from the interactive interpreter.  Notice that
 this is not necessarily the same as what would be sent to ‘STDOUT’ if
 the same code were passed to a non-interactive interpreter running as an
 external process.  For example, compare the following two blocks:
 
      #+BEGIN_SRC python :results output
       print "hello"
       2
       print "bye"
      #+END_SRC
 
      #+RESULTS:
      : hello
      : bye
 
    In non-session mode, the “2” is not printed and does not appear.
 
      #+BEGIN_SRC python :results output :session
       print "hello"
       2
       print "bye"
      #+END_SRC
 
      #+RESULTS:
      : hello
      : 2
      : bye
 
    But in ‘:session’ mode, the interactive interpreter receives input
 “2” and prints out its value, “2”.  (Indeed, the other print statements
 are unnecessary here).
 

Info Catalog org: Header arguments org: Working With Source Code org: Noweb reference syntax