ob-python: content of :prefix argument appended to code file during external evaluation

* lisp/ob-python.el (org-babel-execute:python): Pass the new "prefix"
  header argument through to external evaluation.
  (org-babel-python-evaluate): Pass the new "prefix" header argument
  through to external evaluation.
  (org-babel-python-evaluate-external-process): When specified prepend
  "prefix" to the file used in external evaluation.

lisp/ob-python.el

@@ -58,12 +58,13 @@ This function is called by `org-babel-execute-src-block'."
          (result-type (cdr (assoc :result-type params)))
 	 (return-val (when (and (eq result-type 'value) (not session))
 		       (cdr (assoc :return params))))
+	 (prefix (cdr (assoc :prefix params)))
          (full-body
 	  (org-babel-expand-body:generic
 	   (concat body (if return-val (format "return %s" return-val) ""))
 	   params (org-babel-variable-assignments:python params)))
          (result (org-babel-python-evaluate
-		  session full-body result-type result-params)))
+		  session full-body result-type result-params prefix)))
     (or (cdr (assoc :file params))
         (org-babel-reassemble-table
          result
@@ -181,35 +182,38 @@ def main():
 open('%s', 'w').write( pprint.pformat(main()) )")
 
 (defun org-babel-python-evaluate
-  (session body &optional result-type result-params)
+  (session body &optional result-type result-params prefix)
   "Evaluate BODY as python code."
   (if session
       (org-babel-python-evaluate-session
        session body result-type result-params)
     (org-babel-python-evaluate-external-process
-     body result-type result-params)))
+     body result-type result-params prefix)))
 
 (defun org-babel-python-evaluate-external-process
-  (body &optional result-type result-params)
+  (body &optional result-type result-params prefix)
   "Evaluate BODY in external python process.
 If RESULT-TYPE equals 'output then return standard output as a
 string. If RESULT-TYPE equals 'value then return the value of the
 last statement in BODY, as elisp."
   (case result-type
-    (output (org-babel-eval org-babel-python-command body))
+    (output (org-babel-eval org-babel-python-command
+			    (concat (if prefix (concat prefix "\n") "") body)))
     (value (let ((tmp-file (org-babel-temp-file "python-")))
 	     (org-babel-eval org-babel-python-command
-			     (format
-			      (if (member "pp" result-params)
-				  org-babel-python-pp-wrapper-method
-				org-babel-python-wrapper-method)
-			      (mapconcat
-			       (lambda (line) (format "\t%s" line))
-			       (split-string
-				(org-remove-indentation
-				 (org-babel-trim body))
-				"[\r\n]") "\n")
-			      (org-babel-process-file-name tmp-file 'noquote)))
+			     (concat
+			      (if prefix (concat prefix "\n") "")
+			      (format
+			       (if (member "pp" result-params)
+				   org-babel-python-pp-wrapper-method
+				 org-babel-python-wrapper-method)
+			       (mapconcat
+				(lambda (line) (format "\t%s" line))
+				(split-string
+				 (org-remove-indentation
+				  (org-babel-trim body))
+				 "[\r\n]") "\n")
+			       (org-babel-process-file-name tmp-file 'noquote))))
 	     ((lambda (raw)
 		(if (or (member "code" result-params)
 			(member "pp" result-params))