Merge pull request #3363 from tomchristie/dont-access-settings-on-import

Access settings lazily, not at module import.

rest_framework/fields.py

@@ -885,12 +885,11 @@ class DecimalField(Field):
     }
     MAX_STRING_LENGTH = 1000  # Guard against malicious string inputs.
 
-    coerce_to_string = api_settings.COERCE_DECIMAL_TO_STRING
-
     def __init__(self, max_digits, decimal_places, coerce_to_string=None, max_value=None, min_value=None, **kwargs):
         self.max_digits = max_digits
         self.decimal_places = decimal_places
-        self.coerce_to_string = coerce_to_string if (coerce_to_string is not None) else self.coerce_to_string
+        if coerce_to_string is not None:
+            self.coerce_to_string = coerce_to_string
 
         self.max_value = max_value
         self.min_value = min_value
@@ -970,12 +969,14 @@ class DecimalField(Field):
         return value
 
     def to_representation(self, value):
+        coerce_to_string = getattr(self, 'coerce_to_string', api_settings.COERCE_DECIMAL_TO_STRING)
+
         if not isinstance(value, decimal.Decimal):
             value = decimal.Decimal(six.text_type(value).strip())
 
         quantized = self.quantize(value)
 
-        if not self.coerce_to_string:
+        if not coerce_to_string:
             return quantized
         return '{0:f}'.format(quantized)
 
@@ -997,15 +998,15 @@ class DateTimeField(Field):
         'invalid': _('Datetime has wrong format. Use one of these formats instead: {format}.'),
         'date': _('Expected a datetime but got a date.'),
     }
-    format = api_settings.DATETIME_FORMAT
-    input_formats = api_settings.DATETIME_INPUT_FORMATS
-    default_timezone = timezone.get_default_timezone() if settings.USE_TZ else None
     datetime_parser = datetime.datetime.strptime
 
     def __init__(self, format=empty, input_formats=None, default_timezone=None, *args, **kwargs):
-        self.format = format if format is not empty else self.format
-        self.input_formats = input_formats if input_formats is not None else self.input_formats
-        self.default_timezone = default_timezone if default_timezone is not None else self.default_timezone
+        if format is not empty:
+            self.format = format
+        if input_formats is not None:
+            self.input_formats = input_formats
+        if default_timezone is not None:
+            self.timezone = default_timezone
         super(DateTimeField, self).__init__(*args, **kwargs)
 
     def enforce_timezone(self, value):
@@ -1013,21 +1014,28 @@ class DateTimeField(Field):
         When `self.default_timezone` is `None`, always return naive datetimes.
         When `self.default_timezone` is not `None`, always return aware datetimes.
         """
-        if (self.default_timezone is not None) and not timezone.is_aware(value):
-            return timezone.make_aware(value, self.default_timezone)
-        elif (self.default_timezone is None) and timezone.is_aware(value):
+        field_timezone = getattr(self, 'timezone', self.default_timezone())
+
+        if (field_timezone is not None) and not timezone.is_aware(value):
+            return timezone.make_aware(value, field_timezone)
+        elif (field_timezone is None) and timezone.is_aware(value):
             return timezone.make_naive(value, timezone.UTC())
         return value
 
+    def default_timezone(self):
+        return timezone.get_default_timezone() if settings.USE_TZ else None
+
     def to_internal_value(self, value):
+        input_formats = getattr(self, 'input_formats', api_settings.DATETIME_INPUT_FORMATS)
+
         if isinstance(value, datetime.date) and not isinstance(value, datetime.datetime):
             self.fail('date')
 
         if isinstance(value, datetime.datetime):
             return self.enforce_timezone(value)
 
-        for format in self.input_formats:
-            if format.lower() == ISO_8601:
+        for input_format in input_formats:
+            if input_format.lower() == ISO_8601:
                 try:
                     parsed = parse_datetime(value)
                 except (ValueError, TypeError):
@@ -1037,25 +1045,27 @@ class DateTimeField(Field):
                         return self.enforce_timezone(parsed)
             else:
                 try:
-                    parsed = self.datetime_parser(value, format)
+                    parsed = self.datetime_parser(value, input_format)
                 except (ValueError, TypeError):
                     pass
                 else:
                     return self.enforce_timezone(parsed)
 
-        humanized_format = humanize_datetime.datetime_formats(self.input_formats)
+        humanized_format = humanize_datetime.datetime_formats(input_formats)
         self.fail('invalid', format=humanized_format)
 
     def to_representation(self, value):
-        if self.format is None:
+        output_format = getattr(self, 'format', api_settings.DATETIME_FORMAT)
+
+        if output_format is None:
             return value
 
-        if self.format.lower() == ISO_8601:
+        if output_format.lower() == ISO_8601:
             value = value.isoformat()
             if value.endswith('+00:00'):
                 value = value[:-6] + 'Z'
             return value
-        return value.strftime(self.format)
+        return value.strftime(output_format)
 
 
 class DateField(Field):
@@ -1063,24 +1073,26 @@ class DateField(Field):
         'invalid': _('Date has wrong format. Use one of these formats instead: {format}.'),
         'datetime': _('Expected a date but got a datetime.'),
     }
-    format = api_settings.DATE_FORMAT
-    input_formats = api_settings.DATE_INPUT_FORMATS
     datetime_parser = datetime.datetime.strptime
 
     def __init__(self, format=empty, input_formats=None, *args, **kwargs):
-        self.format = format if format is not empty else self.format
-        self.input_formats = input_formats if input_formats is not None else self.input_formats
+        if format is not empty:
+            self.format = format
+        if input_formats is not None:
+            self.input_formats = input_formats
         super(DateField, self).__init__(*args, **kwargs)
 
     def to_internal_value(self, value):
+        input_formats = getattr(self, 'input_formats', api_settings.DATE_INPUT_FORMATS)
+
         if isinstance(value, datetime.datetime):
             self.fail('datetime')
 
         if isinstance(value, datetime.date):
             return value
 
-        for format in self.input_formats:
-            if format.lower() == ISO_8601:
+        for input_format in input_formats:
+            if input_format.lower() == ISO_8601:
                 try:
                     parsed = parse_date(value)
                 except (ValueError, TypeError):
@@ -1090,20 +1102,22 @@ class DateField(Field):
                         return parsed
             else:
                 try:
-                    parsed = self.datetime_parser(value, format)
+                    parsed = self.datetime_parser(value, input_format)
                 except (ValueError, TypeError):
                     pass
                 else:
                     return parsed.date()
 
-        humanized_format = humanize_datetime.date_formats(self.input_formats)
+        humanized_format = humanize_datetime.date_formats(input_formats)
         self.fail('invalid', format=humanized_format)
 
     def to_representation(self, value):
+        output_format = getattr(self, 'format', api_settings.DATE_FORMAT)
+
         if not value:
             return None
 
-        if self.format is None:
+        if output_format is None:
             return value
 
         # Applying a `DateField` to a datetime value is almost always
@@ -1115,33 +1129,35 @@ class DateField(Field):
             'read-only field and deal with timezone issues explicitly.'
         )
 
-        if self.format.lower() == ISO_8601:
+        if output_format.lower() == ISO_8601:
             if (isinstance(value, str)):
                 value = datetime.datetime.strptime(value, '%Y-%m-%d').date()
             return value.isoformat()
 
-        return value.strftime(self.format)
+        return value.strftime(output_format)
 
 
 class TimeField(Field):
     default_error_messages = {
         'invalid': _('Time has wrong format. Use one of these formats instead: {format}.'),
     }
-    format = api_settings.TIME_FORMAT
-    input_formats = api_settings.TIME_INPUT_FORMATS
     datetime_parser = datetime.datetime.strptime
 
     def __init__(self, format=empty, input_formats=None, *args, **kwargs):
-        self.format = format if format is not empty else self.format
-        self.input_formats = input_formats if input_formats is not None else self.input_formats
+        if format is not empty:
+            self.format = format
+        if input_formats is not None:
+            self.input_formats = input_formats
         super(TimeField, self).__init__(*args, **kwargs)
 
     def to_internal_value(self, value):
+        input_formats = getattr(self, 'input_formats', api_settings.TIME_INPUT_FORMATS)
+
         if isinstance(value, datetime.time):
             return value
 
-        for format in self.input_formats:
-            if format.lower() == ISO_8601:
+        for input_format in input_formats:
+            if input_format.lower() == ISO_8601:
                 try:
                     parsed = parse_time(value)
                 except (ValueError, TypeError):
@@ -1151,17 +1167,19 @@ class TimeField(Field):
                         return parsed
             else:
                 try:
-                    parsed = self.datetime_parser(value, format)
+                    parsed = self.datetime_parser(value, input_format)
                 except (ValueError, TypeError):
                     pass
                 else:
                     return parsed.time()
 
-        humanized_format = humanize_datetime.time_formats(self.input_formats)
+        humanized_format = humanize_datetime.time_formats(input_formats)
         self.fail('invalid', format=humanized_format)
 
     def to_representation(self, value):
-        if self.format is None:
+        output_format = getattr(self, 'format', api_settings.TIME_FORMAT)
+
+        if output_format is None:
             return value
 
         # Applying a `TimeField` to a datetime value is almost always
@@ -1173,9 +1191,9 @@ class TimeField(Field):
             'read-only field and deal with timezone issues explicitly.'
         )
 
-        if self.format.lower() == ISO_8601:
+        if output_format.lower() == ISO_8601:
             return value.isoformat()
-        return value.strftime(self.format)
+        return value.strftime(output_format)
 
 
 class DurationField(Field):
@@ -1318,12 +1336,12 @@ class FileField(Field):
         'empty': _('The submitted file is empty.'),
         'max_length': _('Ensure this filename has at most {max_length} characters (it has {length}).'),
     }
-    use_url = api_settings.UPLOADED_FILES_USE_URL
 
     def __init__(self, *args, **kwargs):
         self.max_length = kwargs.pop('max_length', None)
         self.allow_empty_file = kwargs.pop('allow_empty_file', False)
-        self.use_url = kwargs.pop('use_url', self.use_url)
+        if 'use_url' in kwargs:
+            self.use_url = kwargs.pop('use_url')
         super(FileField, self).__init__(*args, **kwargs)
 
     def to_internal_value(self, data):
@@ -1344,10 +1362,12 @@ class FileField(Field):
         return data
 
     def to_representation(self, value):
+        use_url = getattr(self, 'use_url', api_settings.UPLOADED_FILES_USE_URL)
+
         if not value:
             return None
 
-        if self.use_url:
+        if use_url:
             if not getattr(value, 'url', None):
                 # If the file has not been saved it may not have a URL.
                 return None

rest_framework/serializers.py

@@ -797,7 +797,7 @@ class ModelSerializer(Serializer):
     # you'll also need to ensure you update the `create` method on any generic
     # views, to correctly handle the 'Location' response header for
     # "HTTP 201 Created" responses.
-    url_field_name = api_settings.URL_FIELD_NAME
+    url_field_name = None
 
     # Default `create` and `update` behavior...
     def create(self, validated_data):
@@ -880,6 +880,9 @@ class ModelSerializer(Serializer):
         Return the dict of field names -> field instances that should be
         used for `self.fields` when instantiating the serializer.
         """
+        if self.url_field_name is None:
+            self.url_field_name = api_settings.URL_FIELD_NAME
+
         assert hasattr(self, 'Meta'), (
             'Class {serializer_class} missing "Meta" attribute'.format(
                 serializer_class=self.__class__.__name__

rest_framework/settings.py

@@ -26,8 +26,6 @@ from django.utils import six
 from rest_framework import ISO_8601
 from rest_framework.compat import importlib
 
-USER_SETTINGS = getattr(settings, 'REST_FRAMEWORK', None)
-
 DEFAULTS = {
     # Base API policies
     'DEFAULT_RENDERER_CLASSES': (
@@ -188,10 +186,17 @@ class APISettings(object):
     and return the class, rather than the string literal.
     """
     def __init__(self, user_settings=None, defaults=None, import_strings=None):
-        self.user_settings = user_settings or {}
+        if user_settings:
+            self._user_settings = user_settings
         self.defaults = defaults or DEFAULTS
         self.import_strings = import_strings or IMPORT_STRINGS
 
+    @property
+    def user_settings(self):
+        if not hasattr(self, '_user_settings'):
+            self._user_settings = getattr(settings, 'REST_FRAMEWORK', {})
+        return self._user_settings
+
     def __getattr__(self, attr):
         if attr not in self.defaults.keys():
             raise AttributeError("Invalid API setting: '%s'" % attr)
@@ -212,7 +217,7 @@ class APISettings(object):
         return val
 
 
-api_settings = APISettings(USER_SETTINGS, DEFAULTS, IMPORT_STRINGS)
+api_settings = APISettings(None, DEFAULTS, IMPORT_STRINGS)
 
 
 def reload_api_settings(*args, **kwargs):