From ace2123d2732dbd15920eb71bcec92a9eabebfd5 Mon Sep 17 00:00:00 2001
From: Damien Nozay <dnozay@users.noreply.github.com>
Date: Thu, 11 Dec 2014 14:34:45 -0800
Subject: [PATCH 01/13] Allow to subclass a Field and make it read-only

Rather than subclass a `Field` and override `__init__` you may want a more data-driven approach where the defaults for `read_only`, `write_only` and `allow_null` are specified on the class.

e.g.
```python
class ReadOnlyLink(serializers.HyperlinkedRelatedField)
    read_only = True
```
---
 rest_framework/fields.py | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index aab80982a..d3ccb6591 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -156,13 +156,27 @@ class Field(object):
     default_empty_html = empty
     initial = None
 
-    def __init__(self, read_only=False, write_only=False,
+    # allows to subclass a Field and have defaults on the class.
+    read_only = False
+    write_only = False
+    allow_null = False
+
+    def __init__(self, read_only=None, write_only=None,
                  required=None, default=empty, initial=empty, source=None,
                  label=None, help_text=None, style=None,
-                 error_messages=None, validators=None, allow_null=False):
+                 error_messages=None, validators=None, allow_null=None):
         self._creation_counter = Field._creation_counter
         Field._creation_counter += 1
 
+        if read_only is None:
+            read_only = self.read_only
+
+        if write_only is None:
+            write_only = self.write_only
+
+        if allow_null is None:
+            allow_null = self.allow_null
+
         # If `required` is unset, then use `True` unless a default is provided.
         if required is None:
             required = default is empty and not read_only

From 6e5517ae2d0f15327d5eb9c37b584995fa963d49 Mon Sep 17 00:00:00 2001
From: Damien Nozay <damien.nozay@gmail.com>
Date: Sun, 4 Jan 2015 12:07:35 -0800
Subject: [PATCH 02/13] Allow CharField to specify defaults directly on class

---
 rest_framework/fields.py | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index d3ccb6591..f1950cefa 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -563,18 +563,22 @@ class CharField(Field):
         'min_length': _('Ensure this field has at least {min_length} characters.')
     }
     initial = ''
+    # allows subclasses to change defaults
+    allow_blank = False
+    max_length = None
+    min_length = None
 
     def __init__(self, **kwargs):
-        self.allow_blank = kwargs.pop('allow_blank', False)
-        max_length = kwargs.pop('max_length', None)
-        min_length = kwargs.pop('min_length', None)
+        self.allow_blank = kwargs.pop('allow_blank', self.allow_blank)
+        self.max_length = kwargs.pop('max_length', self.max_length)
+        self.min_length = kwargs.pop('min_length', self.min_length)
         super(CharField, self).__init__(**kwargs)
-        if max_length is not None:
-            message = self.error_messages['max_length'].format(max_length=max_length)
-            self.validators.append(MaxLengthValidator(max_length, message=message))
-        if min_length is not None:
-            message = self.error_messages['min_length'].format(min_length=min_length)
-            self.validators.append(MinLengthValidator(min_length, message=message))
+        if self.max_length is not None:
+            message = self.error_messages['max_length'].format(max_length=self.max_length)
+            self.validators.append(MaxLengthValidator(self.max_length, message=message))
+        if self.min_length is not None:
+            message = self.error_messages['min_length'].format(min_length=self.min_length)
+            self.validators.append(MinLengthValidator(self.min_length, message=message))
 
     def run_validation(self, data=empty):
         # Test for the empty string here so that it does not get validated,

From 399b46ad20f51562b0be64ed1dc0d88d9c777337 Mon Sep 17 00:00:00 2001
From: Damien Nozay <damien.nozay@gmail.com>
Date: Sun, 4 Jan 2015 12:09:53 -0800
Subject: [PATCH 03/13] Allow IntegerField to specify defaults directly on
 class

---
 rest_framework/fields.py | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index f1950cefa..bd746f39f 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -658,17 +658,20 @@ class IntegerField(Field):
         'max_string_length': _('String value too large')
     }
     MAX_STRING_LENGTH = 1000  # Guard against malicious string inputs.
+    # allows subclasses to change defaults
+    max_value = None
+    min_value = None
 
     def __init__(self, **kwargs):
-        max_value = kwargs.pop('max_value', None)
-        min_value = kwargs.pop('min_value', None)
+        self.max_value = kwargs.pop('max_value', self.max_value)
+        self.min_value = kwargs.pop('min_value', self.min_value)
         super(IntegerField, self).__init__(**kwargs)
-        if max_value is not None:
-            message = self.error_messages['max_value'].format(max_value=max_value)
-            self.validators.append(MaxValueValidator(max_value, message=message))
-        if min_value is not None:
-            message = self.error_messages['min_value'].format(min_value=min_value)
-            self.validators.append(MinValueValidator(min_value, message=message))
+        if self.max_value is not None:
+            message = self.error_messages['max_value'].format(max_value=self.max_value)
+            self.validators.append(MaxValueValidator(self.max_value, message=message))
+        if self.min_value is not None:
+            message = self.error_messages['min_value'].format(min_value=self.min_value)
+            self.validators.append(MinValueValidator(self.min_value, message=message))
 
     def to_internal_value(self, data):
         if isinstance(data, six.text_type) and len(data) > self.MAX_STRING_LENGTH:

From b0b4a469e9fd84f1f9c5256cd4bb1f1c6d0aaf55 Mon Sep 17 00:00:00 2001
From: Damien Nozay <damien.nozay@gmail.com>
Date: Sun, 4 Jan 2015 12:12:39 -0800
Subject: [PATCH 04/13] Allow FloatField to specify defaults directly on class

---
 rest_framework/fields.py | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index bd746f39f..6e47ced89 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -695,17 +695,20 @@ class FloatField(Field):
         'max_string_length': _('String value too large')
     }
     MAX_STRING_LENGTH = 1000  # Guard against malicious string inputs.
+    # allows subclasses to change defaults
+    max_value = None
+    min_value = None
 
     def __init__(self, **kwargs):
-        max_value = kwargs.pop('max_value', None)
-        min_value = kwargs.pop('min_value', None)
+        self.max_value = kwargs.pop('max_value', self.max_value)
+        self.min_value = kwargs.pop('min_value', self.min_value)
         super(FloatField, self).__init__(**kwargs)
-        if max_value is not None:
-            message = self.error_messages['max_value'].format(max_value=max_value)
-            self.validators.append(MaxValueValidator(max_value, message=message))
-        if min_value is not None:
-            message = self.error_messages['min_value'].format(min_value=min_value)
-            self.validators.append(MinValueValidator(min_value, message=message))
+        if self.max_value is not None:
+            message = self.error_messages['max_value'].format(max_value=self.max_value)
+            self.validators.append(MaxValueValidator(self.max_value, message=message))
+        if self.min_value is not None:
+            message = self.error_messages['min_value'].format(min_value=self.min_value)
+            self.validators.append(MinValueValidator(self.min_value, message=message))
 
     def to_internal_value(self, data):
         if isinstance(data, six.text_type) and len(data) > self.MAX_STRING_LENGTH:

From 230a395ca4489e6ea489f99c932faa9f27c7c47b Mon Sep 17 00:00:00 2001
From: Damien Nozay <damien.nozay@gmail.com>
Date: Sun, 4 Jan 2015 12:21:34 -0800
Subject: [PATCH 05/13] Allow DecimalField to specify defaults directly on
 class

---
 rest_framework/fields.py | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index 6e47ced89..e7426314d 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -734,20 +734,27 @@ class DecimalField(Field):
         'max_string_length': _('String value too large')
     }
     MAX_STRING_LENGTH = 1000  # Guard against malicious string inputs.
+    # allows subclasses to change defaults
+    max_value = None
+    min_value = None
+    # todo: max_digits = None
+    # todo: decimal_places = None
 
     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):
+    def __init__(self, max_digits, decimal_places, coerce_to_string=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
+        self.max_value = kwargs.pop('max_value', self.max_value)
+        self.min_value = kwargs.pop('min_value', self.min_value)
         super(DecimalField, self).__init__(**kwargs)
-        if max_value is not None:
-            message = self.error_messages['max_value'].format(max_value=max_value)
-            self.validators.append(MaxValueValidator(max_value, message=message))
-        if min_value is not None:
-            message = self.error_messages['min_value'].format(min_value=min_value)
-            self.validators.append(MinValueValidator(min_value, message=message))
+        if self.max_value is not None:
+            message = self.error_messages['max_value'].format(max_value=self.max_value)
+            self.validators.append(MaxValueValidator(self.max_value, message=message))
+        if self.min_value is not None:
+            message = self.error_messages['min_value'].format(min_value=self.min_value)
+            self.validators.append(MinValueValidator(self.min_value, message=message))
 
     def to_internal_value(self, data):
         """

From be661824ac2154d7ec7c674df46682cd6e9b4da4 Mon Sep 17 00:00:00 2001
From: Damien Nozay <damien.nozay@gmail.com>
Date: Sun, 4 Jan 2015 12:27:58 -0800
Subject: [PATCH 06/13] Allow DateTimeField to specify defaults directly on
 class

---
 rest_framework/fields.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index e7426314d..de767c08e 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -828,10 +828,10 @@ class DateTimeField(Field):
     input_formats = api_settings.DATETIME_INPUT_FORMATS
     default_timezone = timezone.get_default_timezone() if settings.USE_TZ else None
 
-    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
+    def __init__(self, *args, **kwargs):
+        self.format = kwargs.pop('format', self.format)
+        self.default_timezone = kwargs.pop('default_timezone', self.default_timezone)
+        self.input_formats = kwargs.pop('input_formats', self.input_formats)
         super(DateTimeField, self).__init__(*args, **kwargs)
 
     def enforce_timezone(self, value):

From ff28a6652df0a6508146086c9441fda15b8fbaff Mon Sep 17 00:00:00 2001
From: Damien Nozay <damien.nozay@gmail.com>
Date: Sun, 4 Jan 2015 12:28:52 -0800
Subject: [PATCH 07/13] Allow DateField to specify defaults directly on class

---
 rest_framework/fields.py | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index de767c08e..46dfe406c 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -824,6 +824,7 @@ class DateTimeField(Field):
         'invalid': _('Datetime has wrong format. Use one of these formats instead: {format}'),
         'date': _('Expected a datetime but got a date.'),
     }
+    # allows subclasses to change defaults
     format = api_settings.DATETIME_FORMAT
     input_formats = api_settings.DATETIME_INPUT_FORMATS
     default_timezone = timezone.get_default_timezone() if settings.USE_TZ else None
@@ -889,12 +890,13 @@ class DateField(Field):
         'invalid': _('Date has wrong format. Use one of these formats instead: {format}'),
         'datetime': _('Expected a date but got a datetime.'),
     }
+    # allows subclasses to change defaults
     format = api_settings.DATE_FORMAT
     input_formats = api_settings.DATE_INPUT_FORMATS
 
-    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
+    def __init__(self, *args, **kwargs):
+        self.format = kwargs.pop('format', self.format)
+        self.input_formats = kwargs.pop('input_formats', self.input_formats)
         super(DateField, self).__init__(*args, **kwargs)
 
     def to_internal_value(self, value):

From 29f494f4473f00fd2975ad881adc468e58ced6c5 Mon Sep 17 00:00:00 2001
From: Damien Nozay <damien.nozay@gmail.com>
Date: Sun, 4 Jan 2015 12:30:29 -0800
Subject: [PATCH 08/13] Allow TimeField to specify defaults directly on class

---
 rest_framework/fields.py | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index 46dfe406c..611005d68 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -948,12 +948,13 @@ class TimeField(Field):
     default_error_messages = {
         'invalid': _('Time has wrong format. Use one of these formats instead: {format}'),
     }
+    # allows subclasses to change defaults
     format = api_settings.TIME_FORMAT
     input_formats = api_settings.TIME_INPUT_FORMATS
 
-    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
+    def __init__(self, *args, **kwargs):
+        self.format = kwargs.pop('format', self.format)
+        self.input_formats = kwargs.pop('input_formats', self.input_formats)
         super(TimeField, self).__init__(*args, **kwargs)
 
     def to_internal_value(self, value):

From 8471a4a2f73effaf964db42f6d622cc6d7b8d305 Mon Sep 17 00:00:00 2001
From: Damien Nozay <damien.nozay@gmail.com>
Date: Sun, 4 Jan 2015 12:33:08 -0800
Subject: [PATCH 09/13] Allow FileField to specify defaults directly on class

---
 rest_framework/fields.py | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index 611005d68..f9c88bc9c 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -1084,11 +1084,14 @@ class FileField(Field):
         'empty': _("The submitted file is empty."),
         'max_length': _('Ensure this filename has at most {max_length} characters (it has {length}).'),
     }
+    # allows subclasses to change defaults
     use_url = api_settings.UPLOADED_FILES_USE_URL
+    max_length = None
+    allow_empty_file = False
 
     def __init__(self, *args, **kwargs):
-        self.max_length = kwargs.pop('max_length', None)
-        self.allow_empty_file = kwargs.pop('allow_empty_file', False)
+        self.max_length = kwargs.pop('max_length', self.max_length)
+        self.allow_empty_file = kwargs.pop('allow_empty_file', self.allow_empty_file)
         self.use_url = kwargs.pop('use_url', self.use_url)
         super(FileField, self).__init__(*args, **kwargs)
 

From 737f663d6976bc37b716411bc55479436d7c0016 Mon Sep 17 00:00:00 2001
From: Damien Nozay <damien.nozay@gmail.com>
Date: Sun, 4 Jan 2015 12:39:10 -0800
Subject: [PATCH 10/13] Allow ModelField to specify defaults directly on class

---
 rest_framework/fields.py | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index f9c88bc9c..df021d724 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -1286,16 +1286,18 @@ class ModelField(Field):
     default_error_messages = {
         'max_length': _('Ensure this field has no more than {max_length} characters.'),
     }
+    # allows subclasses to change defaults
+    max_length = None
 
     def __init__(self, model_field, **kwargs):
         self.model_field = model_field
         # The `max_length` option is supported by Django's base `Field` class,
         # so we'd better support it here.
-        max_length = kwargs.pop('max_length', None)
+        self.max_length = kwargs.pop('max_length', self.max_length)
         super(ModelField, self).__init__(**kwargs)
-        if max_length is not None:
-            message = self.error_messages['max_length'].format(max_length=max_length)
-            self.validators.append(MaxLengthValidator(max_length, message=message))
+        if self.max_length is not None:
+            message = self.error_messages['max_length'].format(max_length=self.max_length)
+            self.validators.append(MaxLengthValidator(self.max_length, message=message))
 
     def to_internal_value(self, data):
         rel = getattr(self.model_field, 'rel', None)

From ae48939c33373d4ffca4851271bed7887e34b344 Mon Sep 17 00:00:00 2001
From: Damien Nozay <damien.nozay@gmail.com>
Date: Sun, 4 Jan 2015 12:58:58 -0800
Subject: [PATCH 11/13] Allow ChoiceField to specify defaults directly on class

---
 rest_framework/fields.py | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index df021d724..1fc36e155 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -1005,8 +1005,18 @@ class ChoiceField(Field):
     default_error_messages = {
         'invalid_choice': _('`{input}` is not a valid choice.')
     }
+    # allows subclasses to change defaults
+    allow_blank = False
+    choices = None
+
+    def __init__(self, *args, **kwargs):
+        if args:
+            choices = args[0]
+        else:
+            choices = kwargs.pop('choices', self.choices)
+        # not available on class or as kwarg
+        assert choices is not None, 'need to specify `choices`.'
 
-    def __init__(self, choices, **kwargs):
         # Allow either single or paired choices style:
         # choices = [1, 2, 3]
         # choices = [(1, 'First'), (2, 'Second'), (3, 'Third')]
@@ -1026,7 +1036,7 @@ class ChoiceField(Field):
             (six.text_type(key), key) for key in self.choices.keys()
         ])
 
-        self.allow_blank = kwargs.pop('allow_blank', False)
+        self.allow_blank = kwargs.pop('allow_blank', self.allow_blank)
 
         super(ChoiceField, self).__init__(**kwargs)
 

From 4881126544e6520b9db36bb14bee34661a3ff95a Mon Sep 17 00:00:00 2001
From: Damien Nozay <damien.nozay@gmail.com>
Date: Mon, 5 Jan 2015 09:49:33 -0800
Subject: [PATCH 12/13] remove '# allows subclasses to change defaults'
 comments

---
 rest_framework/fields.py | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index 1fc36e155..2a2c95f51 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -563,7 +563,6 @@ class CharField(Field):
         'min_length': _('Ensure this field has at least {min_length} characters.')
     }
     initial = ''
-    # allows subclasses to change defaults
     allow_blank = False
     max_length = None
     min_length = None
@@ -658,7 +657,6 @@ class IntegerField(Field):
         'max_string_length': _('String value too large')
     }
     MAX_STRING_LENGTH = 1000  # Guard against malicious string inputs.
-    # allows subclasses to change defaults
     max_value = None
     min_value = None
 
@@ -695,7 +693,6 @@ class FloatField(Field):
         'max_string_length': _('String value too large')
     }
     MAX_STRING_LENGTH = 1000  # Guard against malicious string inputs.
-    # allows subclasses to change defaults
     max_value = None
     min_value = None
 
@@ -734,7 +731,6 @@ class DecimalField(Field):
         'max_string_length': _('String value too large')
     }
     MAX_STRING_LENGTH = 1000  # Guard against malicious string inputs.
-    # allows subclasses to change defaults
     max_value = None
     min_value = None
     # todo: max_digits = None
@@ -824,7 +820,6 @@ class DateTimeField(Field):
         'invalid': _('Datetime has wrong format. Use one of these formats instead: {format}'),
         'date': _('Expected a datetime but got a date.'),
     }
-    # allows subclasses to change defaults
     format = api_settings.DATETIME_FORMAT
     input_formats = api_settings.DATETIME_INPUT_FORMATS
     default_timezone = timezone.get_default_timezone() if settings.USE_TZ else None
@@ -890,7 +885,6 @@ class DateField(Field):
         'invalid': _('Date has wrong format. Use one of these formats instead: {format}'),
         'datetime': _('Expected a date but got a datetime.'),
     }
-    # allows subclasses to change defaults
     format = api_settings.DATE_FORMAT
     input_formats = api_settings.DATE_INPUT_FORMATS
 
@@ -948,7 +942,6 @@ class TimeField(Field):
     default_error_messages = {
         'invalid': _('Time has wrong format. Use one of these formats instead: {format}'),
     }
-    # allows subclasses to change defaults
     format = api_settings.TIME_FORMAT
     input_formats = api_settings.TIME_INPUT_FORMATS
 
@@ -1005,7 +998,6 @@ class ChoiceField(Field):
     default_error_messages = {
         'invalid_choice': _('`{input}` is not a valid choice.')
     }
-    # allows subclasses to change defaults
     allow_blank = False
     choices = None
 
@@ -1094,7 +1086,6 @@ class FileField(Field):
         'empty': _("The submitted file is empty."),
         'max_length': _('Ensure this filename has at most {max_length} characters (it has {length}).'),
     }
-    # allows subclasses to change defaults
     use_url = api_settings.UPLOADED_FILES_USE_URL
     max_length = None
     allow_empty_file = False
@@ -1296,7 +1287,6 @@ class ModelField(Field):
     default_error_messages = {
         'max_length': _('Ensure this field has no more than {max_length} characters.'),
     }
-    # allows subclasses to change defaults
     max_length = None
 
     def __init__(self, model_field, **kwargs):

From 5a899aea1ad7c38dbd1f53cb4238e948cfbf2b8b Mon Sep 17 00:00:00 2001
From: Damien Nozay <damien.nozay@gmail.com>
Date: Mon, 5 Jan 2015 10:14:53 -0800
Subject: [PATCH 13/13] rework Field.__init__ to use either kwargs / class
 attrs.

Precedence is given to kwargs over class attributes.
You can create a subclass of a Field for 99% of your use cases while still
needing a one-off instance where you need to change an attribute; hence
kwargs is still useful.

Other important point is that kwargs is the current de-facto standard for
declaring fields in a serializer.
---
 rest_framework/fields.py | 42 ++++++++++++++++++++++++++--------------
 1 file changed, 27 insertions(+), 15 deletions(-)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index 2a2c95f51..afde52ae2 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -154,28 +154,40 @@ class Field(object):
     }
     default_validators = []
     default_empty_html = empty
-    initial = None
 
-    # allows to subclass a Field and have defaults on the class.
+    # allows subclasses to change defaults
     read_only = False
     write_only = False
+    required = None
+    default = empty
+    initial = None
+    source = None
+    label = None
+    help_text = None
+    style = None
+    error_messages = None
+    validators = None
     allow_null = False
 
-    def __init__(self, read_only=None, write_only=None,
-                 required=None, default=empty, initial=empty, source=None,
-                 label=None, help_text=None, style=None,
-                 error_messages=None, validators=None, allow_null=None):
+    def __init__(self, **kwargs):
         self._creation_counter = Field._creation_counter
         Field._creation_counter += 1
 
-        if read_only is None:
-            read_only = self.read_only
-
-        if write_only is None:
-            write_only = self.write_only
-
-        if allow_null is None:
-            allow_null = self.allow_null
+        # precedence is given to kwargs over class attributes.
+        # you can create a subclass of a Field for maximum reuse while still
+        # needing a one-off instance where you need to change an attribute.
+        read_only = kwargs.pop('read_only', self.read_only)
+        write_only = kwargs.pop('write_only', self.write_only)
+        required = kwargs.pop('required', self.required)
+        default = kwargs.pop('default', self.default)
+        initial = kwargs.pop('initial', self.initial)
+        source = kwargs.pop('source', self.source)
+        label = kwargs.pop('label', self.label)
+        help_text = kwargs.pop('help_text', self.help_text)
+        style = kwargs.pop('style', self.style)
+        error_messages = kwargs.pop('error_messages', self.error_messages)
+        validators = kwargs.pop('validators', self.validators)
+        allow_null = kwargs.pop('allow_null', self.allow_null)
 
         # If `required` is unset, then use `True` unless a default is provided.
         if required is None:
@@ -192,7 +204,7 @@ class Field(object):
         self.required = required
         self.default = default
         self.source = source
-        self.initial = self.initial if (initial is empty) else initial
+        self.initial = initial
         self.label = label
         self.help_text = help_text
         self.style = {} if style is None else style