Fixed #20765 -- Set small values of `step` using exponential notation.

Browsers parse small factors of 10 as 0 under decimal notation.

Thanks to Trac alias matklad for the report and Claude Paroz for the review.

1 files changed, 8 insertions, 2 deletions

diff --git a/django/forms/fields.py b/django/forms/fields.py
index c4bc3fa88c..7711cd65ad 100644
--- a/django/forms/fields.py
+++ b/django/forms/fields.py
@@ -370,8 +370,14 @@ class DecimalField(IntegerField):
 
     def widget_attrs(self, widget):
         attrs = super(DecimalField, self).widget_attrs(widget)
-        if isinstance(widget, NumberInput) and self.decimal_places:
-            attrs['step'] = '0.%s1' % ('0' * (self.decimal_places - 1))
+        if isinstance(widget, NumberInput):
+            if self.decimal_places is not None:
+                # Use exponential notation for small values since they might
+                # be parsed as 0 otherwise. ref #20765
+                step = str(Decimal('1') / 10 ** self.decimal_places).lower()
+            else:
+                step = 'any'
+            attrs.setdefault('step', step)
         return attrs