Add custom widget for "percent" field

so that storage can use "traditional" (0.3612) format but UI can use
"human-friendly" format (36.12 %)

tailbone/forms/widgets.py

@@ -2,7 +2,7 @@
 ################################################################################
 #
 #  Rattail -- Retail Software Framework
-#  Copyright © 2010-2018 Lance Edgar
+#  Copyright © 2010-2019 Lance Edgar
 #
 #  This file is part of Rattail.
 #
@@ -24,10 +24,11 @@
 Form Widgets
 """
 
-from __future__ import unicode_literals, absolute_import
+from __future__ import unicode_literals, absolute_import, division
 
 import json
 import datetime
+import decimal
 
 import six
 
@@ -55,6 +56,35 @@ class NumberInputWidget(dfwidget.TextInputWidget):
     autocomplete = 'off'
 
 
+class PercentInputWidget(dfwidget.TextInputWidget):
+    """
+    Custom text input widget, used for "percent" type fields.  This widget
+    assumes that the underlying storage for the value is a "traditional"
+    percent value, e.g. ``0.36135`` - but the UI should represent this as a
+    "human-friendly" value, e.g. ``36.135 %``.
+    """
+    template = 'percentinput'
+    autocomplete = 'off'
+
+    def serialize(self, field, cstruct, **kw):
+        if cstruct not in (colander.null, None):
+            # convert "traditional" value to "human-friendly"
+            value = decimal.Decimal(cstruct) * 100
+            value = value.quantize(decimal.Decimal('0.001'))
+            cstruct = six.text_type(value)
+        return super(PercentInputWidget, self).serialize(field, cstruct, **kw)
+
+    def deserialize(self, field, pstruct):
+        pstruct = super(PercentInputWidget, self).deserialize(field, pstruct)
+        if pstruct is colander.null:
+            return colander.null
+        # convert "human-friendly" value to "traditional"
+        value = decimal.Decimal(pstruct)
+        value = value.quantize(decimal.Decimal('0.00001'))
+        value /= 100
+        return six.text_type(value)
+
+
 class PlainSelectWidget(dfwidget.SelectWidget):
     template = 'select_plain'