Indentation in Python can cause unfriendly errors

[edwardalee]

It may not be worth much effort to fix this, but the following program generates Python that will not execute:

target Python
main reactor {
  reaction(startup) {=
    # comment
        print("Hello world");
  =}
}

The problem is that the comment is indented less than the code in the reaction body, which is apparently allowed in Python, but the code generator appends a return 0 statement to the generated reaction body, which looks like this:

    def reaction_function_0(self):

        # comment
            print("Hello world");
        return 0

It's not clear to me why a return value is needed for reactions in the Python target. This seems problematic anyway. The following code works correctly without any return value having been specified:

target Python
main reactor {
  state s = 0
  timer t(0, 1s)
  reaction(t) {=
    self.s += 1
    if (self.s % 2 == 0):
      print("odd")
      return
    print("even")
  =}
}

Maybe the return statement is not needed? If this is the case, it could just be removed from generatePythonFunction in PythonReactionGenerator.java.

[edwardalee]

It seems the reason for this generated return statement is that Python does not tolerate empty reaction bodies. The generatePythonFunction method in PythonReactionGenerator.java could be changed to read something like this:

  public static String generatePythonFunction(
      String pythonFunctionName,
      String inits,
      String reactionBody,
      List<String> reactionParameters) {
    String params =
        reactionParameters.size() > 0 ? ", " + String.join(", ", reactionParameters) : "";
    CodeBuilder code = new CodeBuilder();
    code.pr("def " + pythonFunctionName + "(self" + params + "):");
    code.indent();
    code.pr(inits);
    code.pr(reactionBody);
    if (isEmptyOrCommentsOnly(initia) && isEmptyOrCommentsOnly(reactionBody)) {
      // Python does not tolerate an empty reaction body nor one with just comments.
      code.pr("return");
    }
    return code.toString();
  }

However, the isEmptyOrCommentsOnly method would have to be written and tests would need to be added.