fix deprecated warning of inspect

inspect.getargspec is deprecated since Python 3.0

rest_framework/compat.py

@@ -6,6 +6,8 @@ versions of Django/Python, and compatibility wrappers around optional packages.
 # flake8: noqa
 from __future__ import unicode_literals
 
+import inspect
+
 import django
 from django.conf import settings
 from django.db import connection, transaction
@@ -185,3 +187,36 @@ def template_render(template, context=None, request=None):
     # backends template, e.g. django.template.backends.django.Template
     else:
         return template.render(context, request=request)
+
+
+def is_simple_callable(obj):
+    """
+    True if the object is a callable that takes no arguments.
+    """
+    function = inspect.isfunction(obj)
+    method = inspect.ismethod(obj)
+
+    if not (function or method):
+        return False
+
+    # - `inspect.signature` is introduced in Python 3.3
+    # - `inspect.getfullargspec` is introduced in Python 3.0
+    #     and deprecated since Python 3.5
+    # - `inspect.getargspec` is deprecated since Python 3.0
+    if hasattr(inspect, 'signature'):
+        sig = inspect.signature(obj)
+        for name, param in sig.parameters.items():
+            if param.default is not inspect.Parameter.empty:
+                return False
+
+        return True
+    else:
+        if hasattr(inspect, 'getfullargspec'):
+            spec = inspect.getfullargspec(obj)
+            args, defaults = spec.args, spec.defaults
+        else:
+            args, _, _, defaults = inspect.getargspec(obj)
+
+        len_args = len(args) if function else len(args) - 1
+        len_defaults = len(defaults) if defaults else 0
+        return len_args <= len_defaults

rest_framework/fields.py

@@ -30,7 +30,9 @@ from django.utils.ipv6 import clean_ipv6_address
 from django.utils.translation import ugettext_lazy as _
 
 from rest_framework import ISO_8601
-from rest_framework.compat import unicode_repr, unicode_to_repr
+from rest_framework.compat import (
+    is_simple_callable, unicode_repr, unicode_to_repr
+)
 from rest_framework.exceptions import ValidationError
 from rest_framework.settings import api_settings
 from rest_framework.utils import html, humanize_datetime, representation
@@ -46,22 +48,6 @@ class empty:
     pass
 
 
-def is_simple_callable(obj):
-    """
-    True if the object is a callable that takes no arguments.
-    """
-    function = inspect.isfunction(obj)
-    method = inspect.ismethod(obj)
-
-    if not (function or method):
-        return False
-
-    args, _, _, defaults = inspect.getargspec(obj)
-    len_args = len(args) if function else len(args) - 1
-    len_defaults = len(defaults) if defaults else 0
-    return len_args <= len_defaults
-
-
 def get_attribute(instance, attrs):
     """
     Similar to Python's built in `getattr(instance, attr)`,

rest_framework/relations.py

@@ -14,9 +14,8 @@ from django.utils.encoding import smart_text
 from django.utils.six.moves.urllib import parse as urlparse
 from django.utils.translation import ugettext_lazy as _
 
-from rest_framework.fields import (
+from rest_framework.compat import is_simple_callable
-    Field, empty, get_attribute, is_simple_callable, iter_options
+from rest_framework.fields import Field, empty, get_attribute, iter_options
-)
 from rest_framework.reverse import reverse
 from rest_framework.utils import html