add FilePathField, update docs

docs/api-guide/fields.md

@@ -189,6 +189,20 @@ A field that ensures the input is a valid UUID string. The `to_internal_value` m
 
     "de305d54-75b4-431b-adb2-eb6b9e546013"
 
+## FilePathField
+
+A field whose choices are limited to the filenames in a certain directory on the filesystem
+
+Corresponds to `django.forms.fields.FilePathField`.
+
+**Signature:** `FilePathField(path, match=None, recursive=False, allow_files=True, allow_folders=False, required=None, **kwargs)`
+
+- `path` - The absolute filesystem path to a directory from which this FilePathField should get its choice.
+- `match` - A regular expression, as a string, that FilePathField will use to filter filenames.
+- `recursive` - Specifies whether all subdirectories of path should be included.  Default is `False`.
+- `allow_files` - Specifies whether files in the specified location should be included. Default is `True`. Either this or `allow_folders` must be `True`.
+- `allow_folders` - Specifies whether folders in the specified location should be included. Default is `False`. Either this or `allow_files` must be `True`.
+
 ---
 
 # Numeric fields

rest_framework/fields.py

@@ -3,7 +3,9 @@ from django.conf import settings
 from django.core.exceptions import ObjectDoesNotExist
 from django.core.exceptions import ValidationError as DjangoValidationError
 from django.core.validators import RegexValidator
-from django.forms import ImageField as DjangoImageField
+from django.forms import (
+    ImageField as DjangoImageField, FilePathField as DjangoFilePathField
+)
 from django.utils import six, timezone
 from django.utils.dateparse import parse_date, parse_datetime, parse_time
 from django.utils.encoding import is_protected_type, smart_text
@@ -653,6 +655,40 @@ class UUIDField(Field):
         return str(value)
 
 
+class FilePathField(CharField):
+    default_error_messages = {
+        'invalid_choice': _('"{input}" is not a valid path choice.')
+    }
+
+    def __init__(self, path, match=None, recursive=False, allow_files=True,
+                 allow_folders=False, required=None, **kwargs):
+        super(FilePathField, self).__init__(**kwargs)
+        # create field and get options to avoid code duplication
+        field = DjangoFilePathField(
+            path, match=match, recursive=recursive, allow_files=allow_files,
+            allow_folders=allow_folders, required=required
+        )
+
+        self.choices = OrderedDict(field.choices)
+        self.choice_strings_to_values = {
+            six.text_type(key): key for key in self.choices.keys()
+        }
+
+    def to_internal_value(self, data):
+        if data == '' and self.allow_blank:
+            return ''
+
+        try:
+            return self.choice_strings_to_values[six.text_type(data)]
+        except KeyError:
+            self.fail('invalid_choice', input=data)
+
+    def to_representation(self, value):
+        if value in ('', None):
+            return value
+        return self.choice_strings_to_values[six.text_type(value)]
+
+
 # Number types...
 
 class IntegerField(Field):

rest_framework/renderers.py

@@ -301,7 +301,10 @@ class HTMLFormRenderer(BaseRenderer):
         },
         serializers.ListSerializer: {
             'base_template': 'list_fieldset.html'
-        }
+        },
+        serializers.FilePathField: {
+            'base_template': 'select.html',
+        },
     })
 
     def render_field(self, field, parent_style):

tests/test_fields.py

-from decimal import Decimal
-from django.utils import timezone
-from rest_framework import serializers
 import datetime
+import os
+import uuid
+from decimal import Decimal
+
 import django
 import pytest
-import uuid
+from django.utils import timezone
+from rest_framework import serializers
 
 
 # Tests for field keyword arguments and core functionality.
@@ -518,6 +520,24 @@ class TestUUIDField(FieldValues):
     field = serializers.UUIDField()
 
 
+class TestFilePathField(FieldValues):
+    """
+    Valid and invalid values for `FilePathField`
+    """
+
+    valid_inputs = {
+        __file__: __file__,
+    }
+    invalid_inputs = {
+        'wrong_path': ['"wrong_path" is not a valid path choice.']
+    }
+    outputs = {
+    }
+    field = serializers.FilePathField(
+        path=os.path.abspath(os.path.dirname(__file__))
+    )
+
+
 # Number types...
 
 class TestIntegerField(FieldValues):