Simplify string formatting (#4757)

32 files changed, 89 insertions, 89 deletions

diff --git a/src/cryptography/__about__.py b/src/cryptography/__about__.py
index 87890823..759c3037 100644
--- a/src/cryptography/__about__.py
+++ b/src/cryptography/__about__.py
@@ -20,4 +20,4 @@ __author__ = "The cryptography developers"
 __email__ = "cryptography-dev@python.org"
 
 __license__ = "BSD or Apache License, Version 2.0"
-__copyright__ = "Copyright 2013-2017 {0}".format(__author__)
+__copyright__ = "Copyright 2013-2017 {}".format(__author__)
diff --git a/src/cryptography/hazmat/_oid.py b/src/cryptography/hazmat/_oid.py
index cfe906cd..4b08722f 100644
--- a/src/cryptography/hazmat/_oid.py
+++ b/src/cryptography/hazmat/_oid.py
@@ -50,7 +50,7 @@ class ObjectIdentifier(object):
         return not self == other
 
     def __repr__(self):
-        return "<ObjectIdentifier(oid={0}, name={1})>".format(
+        return "<ObjectIdentifier(oid={}, name={})>".format(
             self.dotted_string,
             self._name
         )
diff --git a/src/cryptography/hazmat/backends/openssl/aead.py b/src/cryptography/hazmat/backends/openssl/aead.py
index 73195ff3..1335b4f9 100644
--- a/src/cryptography/hazmat/backends/openssl/aead.py
+++ b/src/cryptography/hazmat/backends/openssl/aead.py
@@ -18,10 +18,10 @@ def _aead_cipher_name(cipher):
     if isinstance(cipher, ChaCha20Poly1305):
         return b"chacha20-poly1305"
     elif isinstance(cipher, AESCCM):
-        return "aes-{0}-ccm".format(len(cipher._key) * 8).encode("ascii")
+        return "aes-{}-ccm".format(len(cipher._key) * 8).encode("ascii")
     else:
         assert isinstance(cipher, AESGCM)
-        return "aes-{0}-gcm".format(len(cipher._key) * 8).encode("ascii")
+        return "aes-{}-gcm".format(len(cipher._key) * 8).encode("ascii")
 
 
 def _aead_setup(backend, cipher_name, key, nonce, tag, tag_len, operation):
diff --git a/src/cryptography/hazmat/backends/openssl/backend.py b/src/cryptography/hazmat/backends/openssl/backend.py
index 0a9bc53a..33a96af2 100644
--- a/src/cryptography/hazmat/backends/openssl/backend.py
+++ b/src/cryptography/hazmat/backends/openssl/backend.py
@@ -187,7 +187,7 @@ class Backend(object):
 
     def _evp_md_from_algorithm(self, algorithm):
         if algorithm.name == "blake2b" or algorithm.name == "blake2s":
-            alg = "{0}{1}".format(
+            alg = "{}{}".format(
                 algorithm.name, algorithm.digest_size * 8
             ).encode("ascii")
         else:
@@ -221,7 +221,7 @@ class Backend(object):
 
     def register_cipher_adapter(self, cipher_cls, mode_cls, adapter):
         if (cipher_cls, mode_cls) in self._cipher_registry:
-            raise ValueError("Duplicate registration for: {0} {1}.".format(
+            raise ValueError("Duplicate registration for: {} {}.".format(
                 cipher_cls, mode_cls)
             )
         self._cipher_registry[cipher_cls, mode_cls] = adapter
@@ -980,7 +980,7 @@ class Backend(object):
                 encode = handlers[extension.oid]
             except KeyError:
                 raise NotImplementedError(
-                    'Extension not supported: {0}'.format(extension.oid)
+                    'Extension not supported: {}'.format(extension.oid)
                 )
 
             ext_struct = encode(self, extension.value)
@@ -1244,7 +1244,7 @@ class Backend(object):
                 else:
                     assert userdata.error == -2
                     raise ValueError(
-                        "Passwords longer than {0} bytes are not supported "
+                        "Passwords longer than {} bytes are not supported "
                         "by this backend.".format(userdata.maxsize - 1)
                     )
             else:
@@ -1356,7 +1356,7 @@ class Backend(object):
             return _EllipticCurvePrivateKey(self, ec_cdata, evp_pkey)
         else:
             raise UnsupportedAlgorithm(
-                "Backend object does not support {0}.".format(curve.name),
+                "Backend object does not support {}.".format(curve.name),
                 _Reasons.UNSUPPORTED_ELLIPTIC_CURVE
             )
 
@@ -1610,7 +1610,7 @@ class Backend(object):
         curve_nid = self._lib.OBJ_sn2nid(curve_name.encode())
         if curve_nid == self._lib.NID_undef:
             raise UnsupportedAlgorithm(
-                "{0} is not a supported elliptic curve".format(curve.name),
+                "{} is not a supported elliptic curve".format(curve.name),
                 _Reasons.UNSUPPORTED_ELLIPTIC_CURVE
             )
         return curve_nid
@@ -2323,7 +2323,7 @@ class GetCipherByName(object):
 
 
 def _get_xts_cipher(backend, cipher, mode):
-    cipher_name = "aes-{0}-xts".format(cipher.key_size // 2)
+    cipher_name = "aes-{}-xts".format(cipher.key_size // 2)
     return backend._lib.EVP_get_cipherbyname(cipher_name.encode("ascii"))
 
 
diff --git a/src/cryptography/hazmat/backends/openssl/ciphers.py b/src/cryptography/hazmat/backends/openssl/ciphers.py
index 66ac5fd6..94b48f52 100644
--- a/src/cryptography/hazmat/backends/openssl/ciphers.py
+++ b/src/cryptography/hazmat/backends/openssl/ciphers.py
@@ -40,7 +40,7 @@ class _CipherContext(object):
             adapter = registry[type(cipher), type(mode)]
         except KeyError:
             raise UnsupportedAlgorithm(
-                "cipher {0} in {1} mode is not supported "
+                "cipher {} in {} mode is not supported "
                 "by this backend.".format(
                     cipher.name, mode.name if mode else mode),
                 _Reasons.UNSUPPORTED_CIPHER
@@ -53,7 +53,7 @@ class _CipherContext(object):
                 msg += "in {0.name} mode ".format(mode)
             msg += (
                 "is not supported by this backend (Your version of OpenSSL "
-                "may be too old. Current version: {0}.)"
+                "may be too old. Current version: {}.)"
             ).format(self._backend.openssl_version_text())
             raise UnsupportedAlgorithm(msg, _Reasons.UNSUPPORTED_CIPHER)
 
@@ -127,7 +127,7 @@ class _CipherContext(object):
     def update_into(self, data, buf):
         if len(buf) < (len(data) + self._block_size_bytes - 1):
             raise ValueError(
-                "buffer must be at least {0} bytes for this "
+                "buffer must be at least {} bytes for this "
                 "payload".format(len(data) + self._block_size_bytes - 1)
             )
 
@@ -207,7 +207,7 @@ class _CipherContext(object):
             )
         if len(tag) < self._mode._min_tag_length:
             raise ValueError(
-                "Authentication tag must be {0} bytes or longer.".format(
+                "Authentication tag must be {} bytes or longer.".format(
                     self._mode._min_tag_length)
             )
         res = self._backend._lib.EVP_CIPHER_CTX_ctrl(
diff --git a/src/cryptography/hazmat/backends/openssl/decode_asn1.py b/src/cryptography/hazmat/backends/openssl/decode_asn1.py
index 007675d4..773189d4 100644
--- a/src/cryptography/hazmat/backends/openssl/decode_asn1.py
+++ b/src/cryptography/hazmat/backends/openssl/decode_asn1.py
@@ -135,7 +135,7 @@ def _decode_general_name(backend, gn):
             if "1" in bits[prefix:]:
                 raise ValueError("Invalid netmask")
 
-            ip = ipaddress.ip_network(base.exploded + u"/{0}".format(prefix))
+            ip = ipaddress.ip_network(base.exploded + u"/{}".format(prefix))
         else:
             ip = ipaddress.ip_address(data)
 
@@ -160,7 +160,7 @@ def _decode_general_name(backend, gn):
     else:
         # x400Address or ediPartyName
         raise x509.UnsupportedGeneralNameType(
-            "{0} is not a supported type".format(
+            "{} is not a supported type".format(
                 x509._GENERAL_NAMES.get(gn.type, gn.type)
             ),
             gn.type
@@ -202,7 +202,7 @@ class _X509ExtensionParser(object):
             )
             if oid in seen_oids:
                 raise x509.DuplicateExtension(
-                    "Duplicate {0} extension found".format(oid), oid
+                    "Duplicate {} extension found".format(oid), oid
                 )
 
             # These OIDs are only supported in OpenSSL 1.1.0+ but we want
@@ -245,7 +245,7 @@ class _X509ExtensionParser(object):
                 if ext_data == backend._ffi.NULL:
                     backend._consume_errors()
                     raise ValueError(
-                        "The {0} extension is invalid and can't be "
+                        "The {} extension is invalid and can't be "
                         "parsed".format(oid)
                     )
 
@@ -698,7 +698,7 @@ def _decode_crl_reason(backend, enum):
     try:
         return x509.CRLReason(_CRL_ENTRY_REASON_CODE_TO_ENUM[code])
     except KeyError:
-        raise ValueError("Unsupported reason code: {0}".format(code))
+        raise ValueError("Unsupported reason code: {}".format(code))
 
 
 def _decode_invalidity_date(backend, inv_date):
@@ -758,7 +758,7 @@ def _asn1_string_to_utf8(backend, asn1_string):
     res = backend._lib.ASN1_STRING_to_UTF8(buf, asn1_string)
     if res == -1:
         raise ValueError(
-            "Unsupported ASN1 string type. Type: {0}".format(asn1_string.type)
+            "Unsupported ASN1 string type. Type: {}".format(asn1_string.type)
         )
 
     backend.openssl_assert(buf[0] != backend._ffi.NULL)
diff --git a/src/cryptography/hazmat/backends/openssl/ec.py b/src/cryptography/hazmat/backends/openssl/ec.py
index a8d69bdf..2ca48091 100644
--- a/src/cryptography/hazmat/backends/openssl/ec.py
+++ b/src/cryptography/hazmat/backends/openssl/ec.py
@@ -62,7 +62,7 @@ def _sn_to_elliptic_curve(backend, sn):
         return ec._CURVE_TYPES[sn]()
     except KeyError:
         raise UnsupportedAlgorithm(
-            "{0} is not a supported elliptic curve".format(sn),
+            "{} is not a supported elliptic curve".format(sn),
             _Reasons.UNSUPPORTED_ELLIPTIC_CURVE
         )
 
diff --git a/src/cryptography/hazmat/backends/openssl/encode_asn1.py b/src/cryptography/hazmat/backends/openssl/encode_asn1.py
index 35575762..61cfd14d 100644
--- a/src/cryptography/hazmat/backends/openssl/encode_asn1.py
+++ b/src/cryptography/hazmat/backends/openssl/encode_asn1.py
@@ -475,7 +475,7 @@ def _encode_general_name(backend, name):
         gn.d.uniformResourceIdentifier = asn1_str
     else:
         raise ValueError(
-            "{0} is an unknown GeneralName type".format(name)
+            "{} is an unknown GeneralName type".format(name)
         )
 
     return gn
diff --git a/src/cryptography/hazmat/backends/openssl/hashes.py b/src/cryptography/hazmat/backends/openssl/hashes.py
index 549fa2bf..7f9d840b 100644
--- a/src/cryptography/hazmat/backends/openssl/hashes.py
+++ b/src/cryptography/hazmat/backends/openssl/hashes.py
@@ -25,7 +25,7 @@ class _HashContext(object):
             evp_md = self._backend._evp_md_from_algorithm(algorithm)
             if evp_md == self._backend._ffi.NULL:
                 raise UnsupportedAlgorithm(
-                    "{0} is not a supported hash on this backend.".format(
+                    "{} is not a supported hash on this backend.".format(
                         algorithm.name),
                     _Reasons.UNSUPPORTED_HASH
                 )
diff --git a/src/cryptography/hazmat/backends/openssl/hmac.py b/src/cryptography/hazmat/backends/openssl/hmac.py
index b23ac649..4b66a610 100644
--- a/src/cryptography/hazmat/backends/openssl/hmac.py
+++ b/src/cryptography/hazmat/backends/openssl/hmac.py
@@ -28,7 +28,7 @@ class _HMACContext(object):
             evp_md = self._backend._evp_md_from_algorithm(algorithm)
             if evp_md == self._backend._ffi.NULL:
                 raise UnsupportedAlgorithm(
-                    "{0} is not a supported hash on this backend".format(
+                    "{} is not a supported hash on this backend".format(
                         algorithm.name),
                     _Reasons.UNSUPPORTED_HASH
                 )
diff --git a/src/cryptography/hazmat/backends/openssl/ocsp.py b/src/cryptography/hazmat/backends/openssl/ocsp.py
index 16dbbc2a..7420f657 100644
--- a/src/cryptography/hazmat/backends/openssl/ocsp.py
+++ b/src/cryptography/hazmat/backends/openssl/ocsp.py
@@ -82,7 +82,7 @@ def _hash_algorithm(backend, cert_id):
         return _OIDS_TO_HASH[oid]
     except KeyError:
         raise UnsupportedAlgorithm(
-            "Signature algorithm OID: {0} not recognized".format(oid)
+            "Signature algorithm OID: {} not recognized".format(oid)
         )
 
 
@@ -134,7 +134,7 @@ class _OCSPResponse(object):
             return x509._SIG_OIDS_TO_HASH[oid]
         except KeyError:
             raise UnsupportedAlgorithm(
-                "Signature algorithm OID:{0} not recognized".format(oid)
+                "Signature algorithm OID:{} not recognized".format(oid)
             )
 
     @property
diff --git a/src/cryptography/hazmat/backends/openssl/rsa.py b/src/cryptography/hazmat/backends/openssl/rsa.py
index 30d59bd8..3e4c2fd2 100644
--- a/src/cryptography/hazmat/backends/openssl/rsa.py
+++ b/src/cryptography/hazmat/backends/openssl/rsa.py
@@ -59,7 +59,7 @@ def _enc_dec_rsa(backend, key, data, padding):
 
     else:
         raise UnsupportedAlgorithm(
-            "{0} is not supported by this backend.".format(
+            "{} is not supported by this backend.".format(
                 padding.name
             ),
             _Reasons.UNSUPPORTED_PADDING
@@ -178,7 +178,7 @@ def _rsa_sig_determine_padding(backend, key, padding, algorithm):
         padding_enum = backend._lib.RSA_PKCS1_PSS_PADDING
     else:
         raise UnsupportedAlgorithm(
-            "{0} is not supported by this backend.".format(padding.name),
+            "{} is not supported by this backend.".format(padding.name),
             _Reasons.UNSUPPORTED_PADDING
         )
 
@@ -197,7 +197,7 @@ def _rsa_sig_setup(backend, padding, algorithm, key, data, init_func):
     if res == 0:
         backend._consume_errors()
         raise UnsupportedAlgorithm(
-            "{0} is not supported by this backend for RSA signing.".format(
+            "{} is not supported by this backend for RSA signing.".format(
                 algorithm.name
             ),
             _Reasons.UNSUPPORTED_HASH
diff --git a/src/cryptography/hazmat/backends/openssl/x509.py b/src/cryptography/hazmat/backends/openssl/x509.py
index b3eb797d..920eaf52 100644
--- a/src/cryptography/hazmat/backends/openssl/x509.py
+++ b/src/cryptography/hazmat/backends/openssl/x509.py
@@ -29,7 +29,7 @@ class _Certificate(object):
         self._x509 = x509
 
     def __repr__(self):
-        return "<Certificate(subject={0}, ...)>".format(self.subject)
+        return "<Certificate(subject={}, ...)>".format(self.subject)
 
     def __eq__(self, other):
         if not isinstance(other, x509.Certificate):
@@ -58,7 +58,7 @@ class _Certificate(object):
             return x509.Version.v3
         else:
             raise x509.InvalidVersion(
-                "{0} is not a valid X509 version".format(version), version
+                "{} is not a valid X509 version".format(version), version
             )
 
     @property
@@ -107,7 +107,7 @@ class _Certificate(object):
             return x509._SIG_OIDS_TO_HASH[oid]
         except KeyError:
             raise UnsupportedAlgorithm(
-                "Signature algorithm OID:{0} not recognized".format(oid)
+                "Signature algorithm OID:{} not recognized".format(oid)
             )
 
     @property
@@ -261,7 +261,7 @@ class _CertificateRevocationList(object):
             return x509._SIG_OIDS_TO_HASH[oid]
         except KeyError:
             raise UnsupportedAlgorithm(
-                "Signature algorithm OID:{0} not recognized".format(oid)
+                "Signature algorithm OID:{} not recognized".format(oid)
             )
 
     @property
@@ -413,7 +413,7 @@ class _CertificateSigningRequest(object):
             return x509._SIG_OIDS_TO_HASH[oid]
         except KeyError:
             raise UnsupportedAlgorithm(
-                "Signature algorithm OID:{0} not recognized".format(oid)
+                "Signature algorithm OID:{} not recognized".format(oid)
             )
 
     @property
diff --git a/src/cryptography/hazmat/primitives/ciphers/algorithms.py b/src/cryptography/hazmat/primitives/ciphers/algorithms.py
index 1f49fd9d..f4d5160b 100644
--- a/src/cryptography/hazmat/primitives/ciphers/algorithms.py
+++ b/src/cryptography/hazmat/primitives/ciphers/algorithms.py
@@ -17,7 +17,7 @@ def _verify_key_size(algorithm, key):
 
     # Verify that the key size matches the expected key size
     if len(key) * 8 not in algorithm.key_sizes:
-        raise ValueError("Invalid key size ({0}) for {1}.".format(
+        raise ValueError("Invalid key size ({}) for {}.".format(
             len(key) * 8, algorithm.name
         ))
     return key
diff --git a/src/cryptography/hazmat/primitives/ciphers/base.py b/src/cryptography/hazmat/primitives/ciphers/base.py
index f8570414..4d5f8d60 100644
--- a/src/cryptography/hazmat/primitives/ciphers/base.py
+++ b/src/cryptography/hazmat/primitives/ciphers/base.py
@@ -179,7 +179,7 @@ class _AEADCipherContext(object):
         self._bytes_processed += data_size
         if self._bytes_processed > self._ctx._mode._MAX_ENCRYPTED_BYTES:
             raise ValueError(
-                "{0} has a maximum encrypted byte limit of {1}".format(
+                "{} has a maximum encrypted byte limit of {}".format(
                     self._ctx._mode.name, self._ctx._mode._MAX_ENCRYPTED_BYTES
                 )
             )
@@ -217,7 +217,7 @@ class _AEADCipherContext(object):
         self._aad_bytes_processed += len(data)
         if self._aad_bytes_processed > self._ctx._mode._MAX_AAD_BYTES:
             raise ValueError(
-                "{0} has a maximum AAD byte limit of {1}".format(
+                "{} has a maximum AAD byte limit of {}".format(
                     self._ctx._mode.name, self._ctx._mode._MAX_AAD_BYTES
                 )
             )
diff --git a/src/cryptography/hazmat/primitives/ciphers/modes.py b/src/cryptography/hazmat/primitives/ciphers/modes.py
index ad91a6e1..78fa1c48 100644
--- a/src/cryptography/hazmat/primitives/ciphers/modes.py
+++ b/src/cryptography/hazmat/primitives/ciphers/modes.py
@@ -72,7 +72,7 @@ def _check_aes_key_length(self, algorithm):
 
 def _check_iv_length(self, algorithm):
     if len(self.initialization_vector) * 8 != algorithm.block_size:
-        raise ValueError("Invalid IV size ({0}) for {1}.".format(
+        raise ValueError("Invalid IV size ({}) for {}.".format(
             len(self.initialization_vector), self.name
         ))
 
@@ -178,7 +178,7 @@ class CTR(object):
     def validate_for_algorithm(self, algorithm):
         _check_aes_key_length(self, algorithm)
         if len(self.nonce) * 8 != algorithm.block_size:
-            raise ValueError("Invalid nonce size ({0}) for {1}.".format(
+            raise ValueError("Invalid nonce size ({}) for {}.".format(
                 len(self.nonce), self.name
             ))
 
@@ -205,7 +205,7 @@ class GCM(object):
                 raise ValueError("min_tag_length must be >= 4")
             if len(tag) < min_tag_length:
                 raise ValueError(
-                    "Authentication tag must be {0} bytes or longer.".format(
+                    "Authentication tag must be {} bytes or longer.".format(
                         min_tag_length)
                 )
         self._tag = tag
diff --git a/src/cryptography/hazmat/primitives/kdf/concatkdf.py b/src/cryptography/hazmat/primitives/kdf/concatkdf.py
index 65b25cdc..7cb63856 100644
--- a/src/cryptography/hazmat/primitives/kdf/concatkdf.py
+++ b/src/cryptography/hazmat/primitives/kdf/concatkdf.py
@@ -24,7 +24,7 @@ def _common_args_checks(algorithm, length, otherinfo):
     max_length = algorithm.digest_size * (2 ** 32 - 1)
     if length > max_length:
         raise ValueError(
-            "Can not derive keys larger than {0} bits.".format(
+            "Can not derive keys larger than {} bits.".format(
                 max_length
             ))
     if otherinfo is not None:
diff --git a/src/cryptography/hazmat/primitives/kdf/hkdf.py b/src/cryptography/hazmat/primitives/kdf/hkdf.py
index 307f91cc..01f0f288 100644
--- a/src/cryptography/hazmat/primitives/kdf/hkdf.py
+++ b/src/cryptography/hazmat/primitives/kdf/hkdf.py
@@ -68,7 +68,7 @@ class HKDFExpand(object):
 
         if length > max_length:
             raise ValueError(
-                "Can not derive keys larger than {0} octets.".format(
+                "Can not derive keys larger than {} octets.".format(
                     max_length
                 ))
 
diff --git a/src/cryptography/hazmat/primitives/kdf/pbkdf2.py b/src/cryptography/hazmat/primitives/kdf/pbkdf2.py
index a47b7bbc..07d8ac67 100644
--- a/src/cryptography/hazmat/primitives/kdf/pbkdf2.py
+++ b/src/cryptography/hazmat/primitives/kdf/pbkdf2.py
@@ -24,7 +24,7 @@ class PBKDF2HMAC(object):
 
         if not backend.pbkdf2_hmac_supported(algorithm):
             raise UnsupportedAlgorithm(
-                "{0} is not supported for PBKDF2 by this backend.".format(
+                "{} is not supported for PBKDF2 by this backend.".format(
                     algorithm.name),
                 _Reasons.UNSUPPORTED_HASH
             )
diff --git a/src/cryptography/hazmat/primitives/kdf/x963kdf.py b/src/cryptography/hazmat/primitives/kdf/x963kdf.py
index fd9d125e..9eb50b0f 100644
--- a/src/cryptography/hazmat/primitives/kdf/x963kdf.py
+++ b/src/cryptography/hazmat/primitives/kdf/x963kdf.py
@@ -26,7 +26,7 @@ class X963KDF(object):
         max_len = algorithm.digest_size * (2 ** 32 - 1)
         if length > max_len:
             raise ValueError(
-                "Can not derive keys larger than {0} bits.".format(max_len))
+                "Can not derive keys larger than {} bits.".format(max_len))
         if sharedinfo is not None:
             utils._check_bytes("sharedinfo", sharedinfo)
 
diff --git a/src/cryptography/utils.py b/src/cryptography/utils.py
index 567600fb..18c2ab3b 100644
--- a/src/cryptography/utils.py
+++ b/src/cryptography/utils.py
@@ -27,14 +27,14 @@ DeprecatedIn25 = CryptographyDeprecationWarning
 
 def _check_bytes(name, value):
     if not isinstance(value, bytes):
-        raise TypeError("{0} must be bytes".format(name))
+        raise TypeError("{} must be bytes".format(name))
 
 
 def _check_byteslike(name, value):
     try:
         memoryview(value)
     except TypeError:
-        raise TypeError("{0} must be bytes-like".format(name))
+        raise TypeError("{} must be bytes-like".format(name))
 
 
 def read_only_property(name):
@@ -97,7 +97,7 @@ def verify_interface(iface, klass):
     for method in iface.__abstractmethods__:
         if not hasattr(klass, method):
             raise InterfaceNotImplemented(
-                "{0} is missing a {1!r} method".format(klass, method)
+                "{} is missing a {!r} method".format(klass, method)
             )
         if isinstance(getattr(iface, method), abc.abstractproperty):
             # Can't properly verify these yet.
@@ -106,8 +106,8 @@ def verify_interface(iface, klass):
         actual = signature(getattr(klass, method))
         if sig != actual:
             raise InterfaceNotImplemented(
-                "{0}.{1}'s signature differs from the expected. Expected: "
-                "{2!r}. Received: {3!r}".format(
+                "{}.{}'s signature differs from the expected. Expected: "
+                "{!r}. Received: {!r}".format(
                     klass, method, sig, actual
                 )
             )
@@ -159,7 +159,7 @@ def deprecated(value, module_name, message, warning_class):
 
 
 def cached_property(func):
-    cached_name = "_cached_{0}".format(func)
+    cached_name = "_cached_{}".format(func)
     sentinel = object()
 
     def inner(instance):
diff --git a/src/cryptography/x509/extensions.py b/src/cryptography/x509/extensions.py
index 88afa310..f027247e 100644
--- a/src/cryptography/x509/extensions.py
+++ b/src/cryptography/x509/extensions.py
@@ -81,7 +81,7 @@ class Extensions(object):
             if ext.oid == oid:
                 return ext
 
-        raise ExtensionNotFound("No {0} extension was found".format(oid), oid)
+        raise ExtensionNotFound("No {} extension was found".format(oid), oid)
 
     def get_extension_for_class(self, extclass):
         if extclass is UnrecognizedExtension:
@@ -96,7 +96,7 @@ class Extensions(object):
                 return ext
 
         raise ExtensionNotFound(
-            "No {0} extension was found".format(extclass), extclass.oid
+            "No {} extension was found".format(extclass), extclass.oid
         )
 
     def __iter__(self):
@@ -110,7 +110,7 @@ class Extensions(object):
 
     def __repr__(self):
         return (
-            "<Extensions({0})>".format(self._extensions)
+            "<Extensions({})>".format(self._extensions)
         )
 
 
@@ -137,7 +137,7 @@ class CRLNumber(object):
         return hash(self.crl_number)
 
     def __repr__(self):
-        return "<CRLNumber({0})>".format(self.crl_number)
+        return "<CRLNumber({})>".format(self.crl_number)
 
     crl_number = utils.read_only_property("_crl_number")
 
@@ -282,7 +282,7 @@ class AuthorityInformationAccess(object):
         return len(self._descriptions)
 
     def __repr__(self):
-        return "<AuthorityInformationAccess({0})>".format(self._descriptions)
+        return "<AuthorityInformationAccess({})>".format(self._descriptions)
 
     def __eq__(self, other):
         if not isinstance(other, AuthorityInformationAccess):
@@ -429,7 +429,7 @@ class CRLDistributionPoints(object):
         return len(self._distribution_points)
 
     def __repr__(self):
-        return "<CRLDistributionPoints({0})>".format(self._distribution_points)
+        return "<CRLDistributionPoints({})>".format(self._distribution_points)
 
     def __eq__(self, other):
         if not isinstance(other, CRLDistributionPoints):
@@ -470,7 +470,7 @@ class FreshestCRL(object):
         return len(self._distribution_points)
 
     def __repr__(self):
-        return "<FreshestCRL({0})>".format(self._distribution_points)
+        return "<FreshestCRL({})>".format(self._distribution_points)
 
     def __eq__(self, other):
         if not isinstance(other, FreshestCRL):
@@ -676,7 +676,7 @@ class CertificatePolicies(object):
         return len(self._policies)
 
     def __repr__(self):
-        return "<CertificatePolicies({0})>".format(self._policies)
+        return "<CertificatePolicies({})>".format(self._policies)
 
     def __eq__(self, other):
         if not isinstance(other, CertificatePolicies):
@@ -837,7 +837,7 @@ class ExtendedKeyUsage(object):
         return len(self._usages)
 
     def __repr__(self):
-        return "<ExtendedKeyUsage({0})>".format(self._usages)
+        return "<ExtendedKeyUsage({})>".format(self._usages)
 
     def __eq__(self, other):
         if not isinstance(other, ExtendedKeyUsage):
@@ -1192,7 +1192,7 @@ class GeneralNames(object):
         return list(objs)
 
     def __repr__(self):
-        return "<GeneralNames({0})>".format(self._general_names)
+        return "<GeneralNames({})>".format(self._general_names)
 
     def __eq__(self, other):
         if not isinstance(other, GeneralNames):
@@ -1227,7 +1227,7 @@ class SubjectAlternativeName(object):
         return self._general_names.get_values_for_type(type)
 
     def __repr__(self):
-        return "<SubjectAlternativeName({0})>".format(self._general_names)
+        return "<SubjectAlternativeName({})>".format(self._general_names)
 
     def __eq__(self, other):
         if not isinstance(other, SubjectAlternativeName):
@@ -1262,7 +1262,7 @@ class IssuerAlternativeName(object):
         return self._general_names.get_values_for_type(type)
 
     def __repr__(self):
-        return "<IssuerAlternativeName({0})>".format(self._general_names)
+        return "<IssuerAlternativeName({})>".format(self._general_names)
 
     def __eq__(self, other):
         if not isinstance(other, IssuerAlternativeName):
@@ -1297,7 +1297,7 @@ class CertificateIssuer(object):
         return self._general_names.get_values_for_type(type)
 
     def __repr__(self):
-        return "<CertificateIssuer({0})>".format(self._general_names)
+        return "<CertificateIssuer({})>".format(self._general_names)
 
     def __eq__(self, other):
         if not isinstance(other, CertificateIssuer):
@@ -1326,7 +1326,7 @@ class CRLReason(object):
         self._reason = reason
 
     def __repr__(self):
-        return "<CRLReason(reason={0})>".format(self._reason)
+        return "<CRLReason(reason={})>".format(self._reason)
 
     def __eq__(self, other):
         if not isinstance(other, CRLReason):
@@ -1354,7 +1354,7 @@ class InvalidityDate(object):
         self._invalidity_date = invalidity_date
 
     def __repr__(self):
-        return "<InvalidityDate(invalidity_date={0})>".format(
+        return "<InvalidityDate(invalidity_date={})>".format(
             self._invalidity_date
         )
 
@@ -1400,7 +1400,7 @@ class PrecertificateSignedCertificateTimestamps(object):
 
     def __repr__(self):
         return (
-            "<PrecertificateSignedCertificateTimestamps({0})>".format(
+            "<PrecertificateSignedCertificateTimestamps({})>".format(
                 list(self)
             )
         )
diff --git a/src/cryptography/x509/general_name.py b/src/cryptography/x509/general_name.py
index fef29c8c..12338415 100644
--- a/src/cryptography/x509/general_name.py
+++ b/src/cryptography/x509/general_name.py
@@ -206,7 +206,7 @@ class UniformResourceIdentifier(object):
         if parsed.port:
             netloc = (
                 idna.encode(parsed.hostname) +
-                ":{0}".format(parsed.port).encode("ascii")
+                ":{}".format(parsed.port).encode("ascii")
             ).decode("ascii")
         else:
             netloc = idna.encode(parsed.hostname).decode("ascii")
@@ -250,7 +250,7 @@ class DirectoryName(object):
     value = utils.read_only_property("_value")
 
     def __repr__(self):
-        return "<DirectoryName(value={0})>".format(self.value)
+        return "<DirectoryName(value={})>".format(self.value)
 
     def __eq__(self, other):
         if not isinstance(other, DirectoryName):
@@ -276,7 +276,7 @@ class RegisteredID(object):
     value = utils.read_only_property("_value")
 
     def __repr__(self):
-        return "<RegisteredID(value={0})>".format(self.value)
+        return "<RegisteredID(value={})>".format(self.value)
 
     def __eq__(self, other):
         if not isinstance(other, RegisteredID):
@@ -314,7 +314,7 @@ class IPAddress(object):
     value = utils.read_only_property("_value")
 
     def __repr__(self):
-        return "<IPAddress(value={0})>".format(self.value)
+        return "<IPAddress(value={})>".format(self.value)
 
     def __eq__(self, other):
         if not isinstance(other, IPAddress):
@@ -344,7 +344,7 @@ class OtherName(object):
     value = utils.read_only_property("_value")
 
     def __repr__(self):
-        return "<OtherName(type_id={0}, value={1!r})>".format(
+        return "<OtherName(type_id={}, value={!r})>".format(
             self.type_id, self.value)
 
     def __eq__(self, other):
diff --git a/src/cryptography/x509/name.py b/src/cryptography/x509/name.py
index 026b79c2..dac5639e 100644
--- a/src/cryptography/x509/name.py
+++ b/src/cryptography/x509/name.py
@@ -190,7 +190,7 @@ class RelativeDistinguishedName(object):
         return len(self._attributes)
 
     def __repr__(self):
-        return "<RelativeDistinguishedName({0})>".format(self.rfc4514_string())
+        return "<RelativeDistinguishedName({})>".format(self.rfc4514_string())
 
 
 class Name(object):
@@ -253,4 +253,4 @@ class Name(object):
         return sum(len(rdn) for rdn in self._attributes)
 
     def __repr__(self):
-        return "<Name({0})>".format(self.rfc4514_string())
+        return "<Name({})>".format(self.rfc4514_string())
diff --git a/tests/conftest.py b/tests/conftest.py
index d858b4f7..fd690ce7 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -14,7 +14,7 @@ from .utils import (
 
 
 def pytest_report_header(config):
-    return "OpenSSL: {0}".format(openssl_backend.openssl_version_text())
+    return "OpenSSL: {}".format(openssl_backend.openssl_version_text())
 
 
 def pytest_addoption(parser):
@@ -43,7 +43,7 @@ def backend(request):
         isinstance(openssl_backend, iface) for iface in required_interfaces
     ):
         pytest.skip(
-            "OpenSSL doesn't implement required interfaces: {0}".format(
+            "OpenSSL doesn't implement required interfaces: {}".format(
                 required_interfaces
             )
         )
diff --git a/tests/hazmat/backends/test_openssl_memleak.py b/tests/hazmat/backends/test_openssl_memleak.py
index 1db103b5..ed22b5db 100644
--- a/tests/hazmat/backends/test_openssl_memleak.py
+++ b/tests/hazmat/backends/test_openssl_memleak.py
@@ -128,7 +128,7 @@ def assert_no_memory_leaks(s, argv=[]):
     env = os.environ.copy()
     env["PYTHONPATH"] = os.pathsep.join(sys.path)
     argv = [
-        sys.executable, "-c", "{0}\n\n{1}".format(s, MEMORY_LEAK_SCRIPT)
+        sys.executable, "-c", "{}\n\n{}".format(s, MEMORY_LEAK_SCRIPT)
     ] + argv
     # Shell out to a fresh Python process because OpenSSL does not allow you to
     # install new memory hooks after the first malloc/free occurs.
diff --git a/tests/hazmat/primitives/test_dsa.py b/tests/hazmat/primitives/test_dsa.py
index efd2239c..9e1acf93 100644
--- a/tests/hazmat/primitives/test_dsa.py
+++ b/tests/hazmat/primitives/test_dsa.py
@@ -36,7 +36,7 @@ def _skip_if_dsa_not_supported(backend, algorithm, p, q, g):
         not backend.dsa_hash_supported(algorithm)
     ):
         pytest.skip(
-            "{0} does not support the provided parameters".format(backend)
+            "{} does not support the provided parameters".format(backend)
         )
 
 
diff --git a/tests/hazmat/primitives/test_ec.py b/tests/hazmat/primitives/test_ec.py
index 7a6d6aff..1f3a67d3 100644
--- a/tests/hazmat/primitives/test_ec.py
+++ b/tests/hazmat/primitives/test_ec.py
@@ -45,7 +45,7 @@ def _skip_ecdsa_vector(backend, curve_type, hash_type):
         curve_type()
     ):
         pytest.skip(
-            "ECDSA not supported with this hash {0} and curve {1}".format(
+            "ECDSA not supported with this hash {} and curve {}".format(
                 hash_type().name, curve_type().name
             )
         )
@@ -54,7 +54,7 @@ def _skip_ecdsa_vector(backend, curve_type, hash_type):
 def _skip_curve_unsupported(backend, curve):
     if not backend.elliptic_curve_supported(curve):
         pytest.skip(
-            "Curve {0} is not supported by this backend {1}".format(
+            "Curve {} is not supported by this backend {}".format(
                 curve.name, backend
             )
         )
@@ -65,7 +65,7 @@ def _skip_exchange_algorithm_unsupported(backend, algorithm, curve):
         algorithm, curve
     ):
         pytest.skip(
-            "Exchange with {0} curve is not supported by {1}".format(
+            "Exchange with {} curve is not supported by {}".format(
                 curve.name, backend
             )
         )
diff --git a/tests/hazmat/primitives/test_rsa.py b/tests/hazmat/primitives/test_rsa.py
index 65d88f54..9a0aaf1a 100644
--- a/tests/hazmat/primitives/test_rsa.py
+++ b/tests/hazmat/primitives/test_rsa.py
@@ -89,7 +89,7 @@ def _build_oaep_sha2_vectors():
             load_vectors_from_file(
                 os.path.join(
                     base_path,
-                    "oaep-{0}-{1}.txt".format(
+                    "oaep-{}-{}.txt".format(
                         mgf1alg.name, oaepalg.name
                     )
                 ),
@@ -112,7 +112,7 @@ def _skip_pss_hash_algorithm_unsupported(backend, hash_alg):
         )
     ):
         pytest.skip(
-            "Does not support {0} in MGF1 using PSS.".format(hash_alg.name)
+            "Does not support {} in MGF1 using PSS.".format(hash_alg.name)
         )
 
 
diff --git a/tests/hazmat/primitives/test_x963_vectors.py b/tests/hazmat/primitives/test_x963_vectors.py
index 4a945d47..c75afa41 100644
--- a/tests/hazmat/primitives/test_x963_vectors.py
+++ b/tests/hazmat/primitives/test_x963_vectors.py
@@ -21,7 +21,7 @@ from ...utils import load_vectors_from_file, load_x963_vectors
 def _skip_hashfn_unsupported(backend, hashfn):
     if not backend.hash_supported(hashfn):
         pytest.skip(
-            "Hash {0} is not supported by this backend {1}".format(
+            "Hash {} is not supported by this backend {}".format(
                 hashfn.name, backend
             )
         )
diff --git a/tests/hazmat/primitives/utils.py b/tests/hazmat/primitives/utils.py
index 811dcf90..4aa5ce71 100644
--- a/tests/hazmat/primitives/utils.py
+++ b/tests/hazmat/primitives/utils.py
@@ -387,13 +387,13 @@ def kbkdf_counter_mode_test(backend, params):
 
     algorithm = supported_algorithms.get(params.get('prf'))
     if algorithm is None or not backend.hmac_supported(algorithm()):
-        pytest.skip("KBKDF does not support algorithm: {0}".format(
+        pytest.skip("KBKDF does not support algorithm: {}".format(
             params.get('prf')
         ))
 
     ctr_loc = supported_counter_locations.get(params.get("ctrlocation"))
     if ctr_loc is None or not isinstance(ctr_loc, CounterLocation):
-        pytest.skip("Does not support counter location: {0}".format(
+        pytest.skip("Does not support counter location: {}".format(
             params.get('ctrlocation')
         ))
 
diff --git a/tests/utils.py b/tests/utils.py
index b4812808..1362e906 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -30,7 +30,7 @@ KeyedHashVector = collections.namedtuple(
 def check_backend_support(backend, item):
     for mark in item.node.iter_markers("supported"):
         if not mark.kwargs["only_if"](backend):
-            pytest.skip("{0} ({1})".format(
+            pytest.skip("{} ({})".format(
                 mark.kwargs["skip_message"], backend
             ))
 
@@ -396,7 +396,7 @@ def load_fips_dsa_sig_vectors(vector_data):
 
         sha_match = sha_regex.match(line)
         if sha_match:
-            digest_algorithm = "SHA-{0}".format(sha_match.group("sha"))
+            digest_algorithm = "SHA-{}".format(sha_match.group("sha"))
 
         if line.startswith("[mod"):
             continue
@@ -511,7 +511,7 @@ def load_fips_ecdsa_signing_vectors(vector_data):
         curve_match = curve_rx.match(line)
         if curve_match:
             curve_name = _ECDSA_CURVE_NAMES[curve_match.group("curve")]
-            digest_name = "SHA-{0}".format(curve_match.group("sha"))
+            digest_name = "SHA-{}".format(curve_match.group("sha"))
 
         elif line.startswith("Msg = "):
             if data is not None: