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.

The line numbers are now counted from the function body if the docstring
is empty.

js/widget.js

@@ -205,18 +205,19 @@ function  signatureValueChanged() {
 
  function updateLineNumbers() {
      const linesSignature = mySignatureCodeMirror.state.doc.toString().split('\n').length;
-     const linesDocstring = myDocstringCodeMirror.state.doc.toString().split('\n').length;
 
+     const docstring = myDocstringCodeMirror.state.doc.toString();
+     const linesDocstring = docstring == "" ? 0 : docstring.split('\n').length;
 
      // increment line numbers in docstring text area by the number of lines in the signature
      myDocstringCodeMirror.dispatch({
- effects: guttercomp.reconfigure(
-     lineNumbers({ formatNumber: n=>linesSignature+n }))
+       effects: guttercomp.reconfigure(
+         lineNumbers({ formatNumber: n=> linesDocstring == 0 ? "" : linesSignature+n }))
      });
 
      myBodyCodeMirror.dispatch({
- effects: guttercomp.reconfigure(
-     lineNumbers({ formatNumber: n=>linesSignature+linesDocstring+n}))
+       effects: guttercomp.reconfigure(
+         lineNumbers({ formatNumber: n=>linesSignature+linesDocstring+n}))
      });
 
  }
@@ -225,7 +226,7 @@ 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

@@ -62,8 +62,6 @@ def _valid_docstring(self, docstring):
             """
             Validate that the docstring do not contain triple double quotes
             """
-            if '"""' in docstring['value']:
-                raise TraitError('The docstring cannot contain triple double quotes (""")')
             return docstring['value']
 
 
@@ -73,7 +71,7 @@ def __init__(  # pylint: disable=too-many-arguments
         self,
         function_name,
         function_parameters="",
-        docstring="\n",
+        docstring=None,
         function_body="",
         code_theme="basicLight",
     ):
@@ -94,7 +92,18 @@ def __init__(  # pylint: disable=too-many-arguments
 
             self.function_name = function_name
             self.function_parameters = function_parameters
-            self.docstring = docstring
+            if docstring is None:
+                # we cannot store docstring as None so we use
+                # a variable to signify that it was None
+                self.docstring = ""
+                self._display_docstring = False
+            elif docstring.startswith("\"") and docstring.endswith("\""):
+                # assume the quotation marks have been added so we do not need to add them
+                self.docstring = docstring
+                self._display_docstring = True
+            else: 
+                self.docstring = f"\"\"\"{docstring}\"\"\""
+                self._display_docstring = True
             self.function_body = function_body
             self.code_theme = code_theme
             self.widget_instance_count_trait=f"{WidgetCodeInput.widget_instance_count}"
@@ -114,7 +123,7 @@ def full_function_code(self):
             including signature, docstring and body
             """
             return build_function(
-                self.function_signature, self.docstring, self.function_body
+                self.function_signature, self.docstring if self._display_docstring else None, self.function_body
             )
 
         @property

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),
     )