Moved has_changed logic from widget to form field

Refs #16612. Thanks Aymeric Augustin for the suggestion.

django/forms/widgets.py

@@ -208,25 +208,6 @@ class Widget(six.with_metaclass(MediaDefiningClass)):
         """
         return data.get(name, None)
 
-    def _has_changed(self, initial, data):
-        """
-        Return True if data differs from initial.
-        """
-        # For purposes of seeing whether something has changed, None is
-        # the same as an empty string, if the data or inital value we get
-        # is None, replace it w/ ''.
-        if data is None:
-            data_value = ''
-        else:
-            data_value = data
-        if initial is None:
-            initial_value = ''
-        else:
-            initial_value = initial
-        if force_text(initial_value) != force_text(data_value):
-            return True
-        return False
-
     def id_for_label(self, id_):
         """
         Returns the HTML ID attribute of this Widget for use by a <label>,
@@ -325,10 +306,6 @@ class FileInput(Input):
         "File widgets take data from FILES, not POST"
         return files.get(name, None)
 
-    def _has_changed(self, initial, data):
-        if data is None:
-            return False
-        return True
 
 FILE_INPUT_CONTRADICTION = object()
 
@@ -426,17 +403,6 @@ class DateInput(TextInput):
             return value.strftime(self.format)
         return value
 
-    def _has_changed(self, initial, data):
-        # If our field has show_hidden_initial=True, initial will be a string
-        # formatted by HiddenInput using formats.localize_input, which is not
-        # necessarily the format used for this widget. Attempt to convert it.
-        try:
-            input_format = formats.get_format('DATE_INPUT_FORMATS')[0]
-            initial = datetime.datetime.strptime(initial, input_format).date()
-        except (TypeError, ValueError):
-            pass
-        return super(DateInput, self)._has_changed(self._format_value(initial), data)
-
 
 class DateTimeInput(TextInput):
     def __init__(self, attrs=None, format=None):
@@ -456,17 +422,6 @@ class DateTimeInput(TextInput):
             return value.strftime(self.format)
         return value
 
-    def _has_changed(self, initial, data):
-        # If our field has show_hidden_initial=True, initial will be a string
-        # formatted by HiddenInput using formats.localize_input, which is not
-        # necessarily the format used for this widget. Attempt to convert it.
-        try:
-            input_format = formats.get_format('DATETIME_INPUT_FORMATS')[0]
-            initial = datetime.datetime.strptime(initial, input_format)
-        except (TypeError, ValueError):
-            pass
-        return super(DateTimeInput, self)._has_changed(self._format_value(initial), data)
-
 
 class TimeInput(TextInput):
     def __init__(self, attrs=None, format=None):
@@ -485,17 +440,6 @@ class TimeInput(TextInput):
             return value.strftime(self.format)
         return value
 
-    def _has_changed(self, initial, data):
-        # If our field has show_hidden_initial=True, initial will be a string
-        # formatted by HiddenInput using formats.localize_input, which is not
-        # necessarily the format used for this  widget. Attempt to convert it.
-        try:
-            input_format = formats.get_format('TIME_INPUT_FORMATS')[0]
-            initial = datetime.datetime.strptime(initial, input_format).time()
-        except (TypeError, ValueError):
-            pass
-        return super(TimeInput, self)._has_changed(self._format_value(initial), data)
-
 
 # Defined at module level so that CheckboxInput is picklable (#17976)
 def boolean_check(v):
@@ -530,13 +474,6 @@ class CheckboxInput(Widget):
             value = values.get(value.lower(), value)
         return bool(value)
 
-    def _has_changed(self, initial, data):
-        # Sometimes data or initial could be None or '' which should be the
-        # same thing as False.
-        if initial == 'False':
-            # show_hidden_initial may have transformed False to 'False'
-            initial = False
-        return bool(initial) != bool(data)
 
 class Select(Widget):
     allow_multiple_selected = False
@@ -612,14 +549,6 @@ class NullBooleanSelect(Select):
                 'False': False,
                 False: False}.get(value, None)
 
-    def _has_changed(self, initial, data):
-        # For a NullBooleanSelect, None (unknown) and False (No)
-        # are not the same
-        if initial is not None:
-            initial = bool(initial)
-        if data is not None:
-            data = bool(data)
-        return initial != data
 
 class SelectMultiple(Select):
     allow_multiple_selected = True
@@ -639,16 +568,6 @@ class SelectMultiple(Select):
             return data.getlist(name)
         return data.get(name, None)
 
-    def _has_changed(self, initial, data):
-        if initial is None:
-            initial = []
-        if data is None:
-            data = []
-        if len(initial) != len(data):
-            return True
-        initial_set = set([force_text(value) for value in initial])
-        data_set = set([force_text(value) for value in data])
-        return data_set != initial_set
 
 @python_2_unicode_compatible
 class RadioInput(SubWidget):
@@ -844,17 +763,6 @@ class MultiWidget(Widget):
     def value_from_datadict(self, data, files, name):
         return [widget.value_from_datadict(data, files, name + '_%s' % i) for i, widget in enumerate(self.widgets)]
 
-    def _has_changed(self, initial, data):
-        if initial is None:
-            initial = ['' for x in range(0, len(data))]
-        else:
-            if not isinstance(initial, list):
-                initial = self.decompress(initial)
-        for widget, initial, data in zip(self.widgets, initial, data):
-            if widget._has_changed(initial, data):
-                return True
-        return False
-
     def format_output(self, rendered_widgets):
         """
         Given a list of rendered widgets (as strings), returns a Unicode string