Simplify implementing sequence methods (#4987)

* Simplify implementing sequence methods

* flake8

1 files changed, 31 insertions, 94 deletions

diff --git a/src/cryptography/x509/extensions.py b/src/cryptography/x509/extensions.py
index 5bef9945..f60075a8 100644
--- a/src/cryptography/x509/extensions.py
+++ b/src/cryptography/x509/extensions.py
@@ -70,6 +70,19 @@ def _key_identifier_from_public_key(public_key):
     return hashlib.sha1(data).digest()
 
 
+def _make_sequence_methods(field_name):
+    def len_method(self):
+        return len(getattr(self, field_name))
+
+    def iter_method(self):
+        return iter(getattr(self, field_name))
+
+    def getitem_method(self, idx):
+        return getattr(self, field_name)[idx]
+
+    return len_method, iter_method, getitem_method
+
+
 class DuplicateExtension(Exception):
     def __init__(self, msg, oid):
         super(DuplicateExtension, self).__init__(msg)
@@ -118,14 +131,7 @@ class Extensions(object):
             "No {} extension was found".format(extclass), extclass.oid
         )
 
-    def __iter__(self):
-        return iter(self._extensions)
-
-    def __len__(self):
-        return len(self._extensions)
-
-    def __getitem__(self, idx):
-        return self._extensions[idx]
+    __len__, __iter__, __getitem__ = _make_sequence_methods("_extensions")
 
     def __repr__(self):
         return (
@@ -307,11 +313,7 @@ class AuthorityInformationAccess(object):
 
         self._descriptions = descriptions
 
-    def __iter__(self):
-        return iter(self._descriptions)
-
-    def __len__(self):
-        return len(self._descriptions)
+    __len__, __iter__, __getitem__ = _make_sequence_methods("_descriptions")
 
     def __repr__(self):
         return "<AuthorityInformationAccess({})>".format(self._descriptions)
@@ -325,9 +327,6 @@ class AuthorityInformationAccess(object):
     def __ne__(self, other):
         return not self == other
 
-    def __getitem__(self, idx):
-        return self._descriptions[idx]
-
     def __hash__(self):
         return hash(tuple(self._descriptions))
 
@@ -454,11 +453,9 @@ class CRLDistributionPoints(object):
 
         self._distribution_points = distribution_points
 
-    def __iter__(self):
-        return iter(self._distribution_points)
-
-    def __len__(self):
-        return len(self._distribution_points)
+    __len__, __iter__, __getitem__ = _make_sequence_methods(
+        "_distribution_points"
+    )
 
     def __repr__(self):
         return "<CRLDistributionPoints({})>".format(self._distribution_points)
@@ -472,9 +469,6 @@ class CRLDistributionPoints(object):
     def __ne__(self, other):
         return not self == other
 
-    def __getitem__(self, idx):
-        return self._distribution_points[idx]
-
     def __hash__(self):
         return hash(tuple(self._distribution_points))
 
@@ -495,11 +489,9 @@ class FreshestCRL(object):
 
         self._distribution_points = distribution_points
 
-    def __iter__(self):
-        return iter(self._distribution_points)
-
-    def __len__(self):
-        return len(self._distribution_points)
+    __len__, __iter__, __getitem__ = _make_sequence_methods(
+        "_distribution_points"
+    )
 
     def __repr__(self):
         return "<FreshestCRL({})>".format(self._distribution_points)
@@ -513,9 +505,6 @@ class FreshestCRL(object):
     def __ne__(self, other):
         return not self == other
 
-    def __getitem__(self, idx):
-        return self._distribution_points[idx]
-
     def __hash__(self):
         return hash(tuple(self._distribution_points))
 
@@ -701,11 +690,7 @@ class CertificatePolicies(object):
 
         self._policies = policies
 
-    def __iter__(self):
-        return iter(self._policies)
-
-    def __len__(self):
-        return len(self._policies)
+    __len__, __iter__, __getitem__ = _make_sequence_methods("_policies")
 
     def __repr__(self):
         return "<CertificatePolicies({})>".format(self._policies)
@@ -719,9 +704,6 @@ class CertificatePolicies(object):
     def __ne__(self, other):
         return not self == other
 
-    def __getitem__(self, idx):
-        return self._policies[idx]
-
     def __hash__(self):
         return hash(tuple(self._policies))
 
@@ -862,11 +844,7 @@ class ExtendedKeyUsage(object):
 
         self._usages = usages
 
-    def __iter__(self):
-        return iter(self._usages)
-
-    def __len__(self):
-        return len(self._usages)
+    __len__, __iter__, __getitem__ = _make_sequence_methods("_usages")
 
     def __repr__(self):
         return "<ExtendedKeyUsage({})>".format(self._usages)
@@ -941,11 +919,7 @@ class TLSFeature(object):
 
         self._features = features
 
-    def __iter__(self):
-        return iter(self._features)
-
-    def __len__(self):
-        return len(self._features)
+    __len__, __iter__, __getitem__ = _make_sequence_methods("_features")
 
     def __repr__(self):
         return "<TLSFeature(features={0._features})>".format(self)
@@ -956,9 +930,6 @@ class TLSFeature(object):
 
         return self._features == other._features
 
-    def __getitem__(self, idx):
-        return self._features[idx]
-
     def __ne__(self, other):
         return not self == other
 
@@ -1237,12 +1208,7 @@ class GeneralNames(object):
             )
 
         self._general_names = general_names
-
-    def __iter__(self):
-        return iter(self._general_names)
-
-    def __len__(self):
-        return len(self._general_names)
+    __len__, __iter__, __getitem__ = _make_sequence_methods("_general_names")
 
     def get_values_for_type(self, type):
         # Return the value of each GeneralName, except for OtherName instances
@@ -1265,9 +1231,6 @@ class GeneralNames(object):
     def __ne__(self, other):
         return not self == other
 
-    def __getitem__(self, idx):
-        return self._general_names[idx]
-
     def __hash__(self):
         return hash(tuple(self._general_names))
 
@@ -1279,11 +1242,7 @@ class SubjectAlternativeName(object):
     def __init__(self, general_names):
         self._general_names = GeneralNames(general_names)
 
-    def __iter__(self):
-        return iter(self._general_names)
-
-    def __len__(self):
-        return len(self._general_names)
+    __len__, __iter__, __getitem__ = _make_sequence_methods("_general_names")
 
     def get_values_for_type(self, type):
         return self._general_names.get_values_for_type(type)
@@ -1297,9 +1256,6 @@ class SubjectAlternativeName(object):
 
         return self._general_names == other._general_names
 
-    def __getitem__(self, idx):
-        return self._general_names[idx]
-
     def __ne__(self, other):
         return not self == other
 
@@ -1314,11 +1270,7 @@ class IssuerAlternativeName(object):
     def __init__(self, general_names):
         self._general_names = GeneralNames(general_names)
 
-    def __iter__(self):
-        return iter(self._general_names)
-
-    def __len__(self):
-        return len(self._general_names)
+    __len__, __iter__, __getitem__ = _make_sequence_methods("_general_names")
 
     def get_values_for_type(self, type):
         return self._general_names.get_values_for_type(type)
@@ -1335,9 +1287,6 @@ class IssuerAlternativeName(object):
     def __ne__(self, other):
         return not self == other
 
-    def __getitem__(self, idx):
-        return self._general_names[idx]
-
     def __hash__(self):
         return hash(self._general_names)
 
@@ -1349,11 +1298,7 @@ class CertificateIssuer(object):
     def __init__(self, general_names):
         self._general_names = GeneralNames(general_names)
 
-    def __iter__(self):
-        return iter(self._general_names)
-
-    def __len__(self):
-        return len(self._general_names)
+    __len__, __iter__, __getitem__ = _make_sequence_methods("_general_names")
 
     def get_values_for_type(self, type):
         return self._general_names.get_values_for_type(type)
@@ -1370,9 +1315,6 @@ class CertificateIssuer(object):
     def __ne__(self, other):
         return not self == other
 
-    def __getitem__(self, idx):
-        return self._general_names[idx]
-
     def __hash__(self):
         return hash(self._general_names)
 
@@ -1451,14 +1393,9 @@ class PrecertificateSignedCertificateTimestamps(object):
             )
         self._signed_certificate_timestamps = signed_certificate_timestamps
 
-    def __iter__(self):
-        return iter(self._signed_certificate_timestamps)
-
-    def __len__(self):
-        return len(self._signed_certificate_timestamps)
-
-    def __getitem__(self, idx):
-        return self._signed_certificate_timestamps[idx]
+    __len__, __iter__, __getitem__ = _make_sequence_methods(
+        "_signed_certificate_timestamps"
+    )
 
     def __repr__(self):
         return (