Allow docstring to use single quotes and to not be displayed

By specifying None for the docstring no docstring is displayed. By
specifying the quotation mark in the docstring the docstring is not
put into triple quotes allowing a docstring in signle quotes.

The implementation puts the responsibility to add the correct quotation
marks to the python side so we can be more flexible.

js/widget.js

@@ -225,7 +225,7 @@ function  signatureValueChanged() {
             // Set the value from python into the CodeMirror widget in the
             // frontend.
 
-            const newDocstring = '"""' + model.get('docstring') + '"""';
+            const newDocstring = model.get('docstring');
 
             if (newDocstring !== myDocstringCodeMirror.state.doc.toString()) {
                 myDocstringCodeMirror.dispatch({

src/widget_code_input/__init__.py

@@ -73,7 +73,7 @@ def __init__(  # pylint: disable=too-many-arguments
         self,
         function_name,
         function_parameters="",
-        docstring="\n",
+        docstring=None,
         function_body="",
         code_theme="basicLight",
     ):
@@ -94,7 +94,15 @@ def __init__(  # pylint: disable=too-many-arguments
 
             self.function_name = function_name
             self.function_parameters = function_parameters
-            self.docstring = docstring
+            if docstring is not None and '"""' in docstring:
+                raise ValueError('Triple double quotes (""") not allowed in docstring')
+            if docstring is None:
+                self.docstring = ""
+            elif docstring.startswith("\"") and docstring.endswith("\""):
+                # assume the quotation marks have been added so we do not need to add them
+                self.docstring = docstring
+            else: 
+                self.docstring = f"\"\"\"{docstring}\"\"\""
             self.function_body = function_body
             self.code_theme = code_theme
             self.widget_instance_count_trait=f"{WidgetCodeInput.widget_instance_count}"

src/widget_code_input/utils.py

@@ -47,12 +47,11 @@ def build_pre_body(signature, docstring, indent_level=4):
     :param docstring: the (unindented) docstring
     :param indent_level: integer number of spaces to prepend to the docstring
     """
-    if '"""' in docstring:
-        raise ValueError('Triple double quotes (""") not allowed in docstring')
 
     return "{}\n{}".format(
         signature,
-        prepend_indent('"""{}"""'.format(docstring), indent_level=indent_level),
+        prepend_indent('' if docstring is None else '"""{}"""'.format(docstring),
+                       indent_level=indent_level),
     )