diff --git a/awscli/customizations/cloudformation/artifact_exporter.py b/awscli/customizations/cloudformation/artifact_exporter.py
index 20f955305066..80158c4ad73e 100644
--- a/awscli/customizations/cloudformation/artifact_exporter.py
+++ b/awscli/customizations/cloudformation/artifact_exporter.py
@@ -289,7 +289,7 @@ class ResourceWithS3UrlDict(Resource):
     VERSION_PROPERTY = None
 
     def __init__(self, uploader):
-        super(ResourceWithS3UrlDict, self).__init__(uploader)
+        super().__init__(uploader)
 
     def do_export(self, resource_id, resource_dict, parent_dir):
         """
@@ -444,7 +444,7 @@ class CloudFormationStackResource(Resource):
     PROPERTY_NAME = "TemplateURL"
 
     def __init__(self, uploader):
-        super(CloudFormationStackResource, self).__init__(uploader)
+        super().__init__(uploader)
 
     def do_export(self, resource_id, resource_dict, parent_dir):
         """
diff --git a/awscli/customizations/cloudtrail/utils.py b/awscli/customizations/cloudtrail/utils.py
index 995b32fcace4..3ade7383bd22 100644
--- a/awscli/customizations/cloudtrail/utils.py
+++ b/awscli/customizations/cloudtrail/utils.py
@@ -28,7 +28,7 @@ def get_trail_by_arn(cloudtrail_client, trail_arn):
     for trail in trails:
         if trail.get("TrailARN", None) == trail_arn:
             return trail
-    raise ValueError("A trail could not be found for %s" % trail_arn)
+    raise ValueError(f"A trail could not be found for {trail_arn}")
 
 
 def format_date(date):
@@ -45,7 +45,7 @@ def parse_date(date_string):
     try:
         return parser.parse(date_string)
     except ValueError:
-        raise ValueError("Unable to parse date value: %s" % date_string)
+        raise ValueError(f"Unable to parse date value: {date_string}")
 
 
 class PublicKeyProvider:
@@ -94,5 +94,5 @@ def get_public_key(self, signature_generate_time, public_key_fingerprint):
                 return key["Value"]
 
         raise RuntimeError(
-            "No public keys found for key with fingerprint: %s" % public_key_fingerprint
+            f"No public keys found for key with fingerprint: {public_key_fingerprint}"
         )
diff --git a/awscli/customizations/cloudtrail/validation.py b/awscli/customizations/cloudtrail/validation.py
index fb4518535c66..6df84ab9e87a 100644
--- a/awscli/customizations/cloudtrail/validation.py
+++ b/awscli/customizations/cloudtrail/validation.py
@@ -66,7 +66,7 @@ def parse_date(date_string):
         return parser.parse(date_string)
     except ValueError:
         raise ParamValidationError(
-            'Unable to parse date value: %s' % date_string
+            f'Unable to parse date value: {date_string}'
         )
 
 
@@ -77,7 +77,7 @@ def assert_cloudtrail_arn_is_valid(trail_arn):
     pattern = re.compile(r'arn:.+:cloudtrail:.+:\d{12}:trail/.+')
     if not pattern.match(trail_arn):
         raise ParamValidationError(
-            'Invalid trail ARN provided: %s' % trail_arn
+            f'Invalid trail ARN provided: {trail_arn}'
         )
 
 
@@ -202,17 +202,16 @@ class DigestError(ValueError):
 class DigestSignatureError(DigestError):
     """Exception raised when a digest signature is invalid"""
     def __init__(self, bucket, key):
-        message = ('Digest file\ts3://%s/%s\tINVALID: signature verification '
-                   'failed') % (bucket, key)
-        super(DigestSignatureError, self).__init__(message)
+        message = (f'Digest file\ts3://{bucket}/{key}\tINVALID: signature verification '
+                   'failed')
+        super().__init__(message)
 
 
 class InvalidDigestFormat(DigestError):
     """Exception raised when a digest has an invalid format"""
     def __init__(self, bucket, key):
-        message = 'Digest file\ts3://%s/%s\tINVALID: invalid format' % (bucket,
-                                                                        key)
-        super(InvalidDigestFormat, self).__init__(message)
+        message = f'Digest file\ts3://{bucket}/{key}\tINVALID: invalid format'
+        super().__init__(message)
 
 
 class DigestProvider:
@@ -444,8 +443,7 @@ def traverse(self, start_date, end_date=None):
                 key, end_date = self._find_next_digest(
                     digests=digests, bucket=bucket, last_key=key,
                     last_start_date=last_start_date, cb=self._on_invalid,
-                    message='Digest file\ts3://%s/%s\tINVALID: %s'
-                            % (bucket, key, str(e)))
+                    message=f'Digest file\ts3://{bucket}/{key}\tINVALID: {str(e)}')
 
     def _load_digests(self, bucket, prefix, start_date, end_date):
         return self.digest_provider.load_digest_keys_in_range(
@@ -502,16 +500,14 @@ def _load_and_validate_digest(self, public_keys, bucket, key):
         if digest_data['digestS3Bucket'] != bucket \
                 or digest_data['digestS3Object'] != key:
             raise DigestError(
-                ('Digest file\ts3://%s/%s\tINVALID: has been moved from its '
-                 'original location') % (bucket, key))
+                f'Digest file\ts3://{bucket}/{key}\tINVALID: has been moved from its '
+                 'original location')
         # Get the public keys in the given time range.
         fingerprint = digest_data['digestPublicKeyFingerprint']
         if fingerprint not in public_keys:
             raise DigestError(
-                ('Digest file\ts3://%s/%s\tINVALID: public key not found in '
-                 'region %s for fingerprint %s') %
-                (bucket, key, self.digest_provider.trail_home_region,
-                 fingerprint))
+                f'Digest file\ts3://{bucket}/{key}\tINVALID: public key not found in '
+                 f'region {self.digest_provider.trail_home_region} for fingerprint {fingerprint}')
         public_key_hex = public_keys[fingerprint]['Value']
         self._digest_validator.validate(
             bucket, key, public_key_hex, digest_data, digest)
@@ -523,9 +519,7 @@ def _load_public_keys(self, start_date, end_date):
             start_date, end_date)
         if not public_keys:
             raise RuntimeError(
-                'No public keys found between %s and %s' %
-                (format_display_date(start_date),
-                 format_display_date(end_date)))
+                f'No public keys found between {format_display_date(start_date)} and {format_display_date(end_date)}')
         return public_keys
 
 
@@ -554,9 +548,8 @@ def validate(self, bucket, key, public_key, digest_data, inflated_digest):
             public_key = RSA.new_public_key_from_der_data(decoded_key)
         except RuntimeError:
             raise DigestError(
-                ('Digest file\ts3://%s/%s\tINVALID: Unable to load PKCS #1 key'
-                 ' with fingerprint %s')
-                % (bucket, key, digest_data['digestPublicKeyFingerprint']))
+                ('Digest file\ts3://{}/{}\tINVALID: Unable to load PKCS #1 key'
+                 ' with fingerprint {}').format(bucket, key, digest_data['digestPublicKeyFingerprint']))
 
         to_sign = self._create_string_to_sign(digest_data, inflated_digest)
         signature_bytes = binascii.unhexlify(digest_data['_signature'])
@@ -577,7 +570,7 @@ def _create_string_to_sign(self, digest_data, inflated_digest):
         if previous_signature is None:
             # The value must be 'null' to match the Java implementation.
             previous_signature = 'null'
-        string_to_sign = "%s\n%s/%s\n%s\n%s" % (
+        string_to_sign = "{}\n{}/{}\n{}\n{}".format(
             digest_data['digestEndTime'],
             digest_data['digestS3Bucket'],
             digest_data['digestS3Object'],
@@ -668,7 +661,7 @@ class CloudTrailValidateLogs(BasicCommand):
     ]
 
     def __init__(self, session):
-        super(CloudTrailValidateLogs, self).__init__(session)
+        super().__init__(session)
         self.trail_arn = None
         self.is_verbose = False
         self.start_time = None
@@ -750,8 +743,7 @@ def _call(self):
             self._track_found_times(digest)
             self._valid_digests += 1
             self._write_status(
-                'Digest file\ts3://%s/%s\tvalid'
-                % (digest['digestS3Bucket'], digest['digestS3Object']))
+                'Digest file\ts3://{}/{}\tvalid'.format(digest['digestS3Bucket'], digest['digestS3Object']))
             if not digest['logFiles']:
                 continue
             for log in digest['logFiles']:
@@ -790,8 +782,7 @@ def _download_log(self, log):
                 self._on_log_invalid(log)
             else:
                 self._valid_logs += 1
-                self._write_status('Log file\ts3://%s/%s\tvalid'
-                                    % (log['s3Bucket'], log['s3Object']))
+                self._write_status('Log file\ts3://{}/{}\tvalid'.format(log['s3Bucket'], log['s3Object']))
         except ClientError as e:
             if e.response['Error']['Code'] != 'NoSuchKey':
                 raise
@@ -802,35 +793,29 @@ def _download_log(self, log):
     def _write_status(self, message, is_error=False):
         if is_error:
             if self._is_last_status_double_space:
-                sys.stderr.write("%s\n\n" % message)
+                sys.stderr.write(f"{message}\n\n")
             else:
-                sys.stderr.write("\n%s\n\n" % message)
+                sys.stderr.write(f"\n{message}\n\n")
             self._is_last_status_double_space = True
         elif self.is_verbose:
             self._is_last_status_double_space = False
-            sys.stdout.write("%s\n" % message)
+            sys.stdout.write(f"{message}\n")
 
     def _write_startup_text(self):
         sys.stdout.write(
-            'Validating log files for trail %s between %s and %s\n\n'
-            % (self.trail_arn, format_display_date(self.start_time),
-               format_display_date(self.end_time)))
+            f'Validating log files for trail {self.trail_arn} between {format_display_date(self.start_time)} and {format_display_date(self.end_time)}\n\n')
 
     def _write_summary_text(self):
         if not self._is_last_status_double_space:
             sys.stdout.write('\n')
-        sys.stdout.write('Results requested for %s to %s\n'
-                         % (format_display_date(self.start_time),
-                            format_display_date(self.end_time)))
+        sys.stdout.write(f'Results requested for {format_display_date(self.start_time)} to {format_display_date(self.end_time)}\n')
         if not self._valid_digests and not self._invalid_digests:
             sys.stdout.write('No digests found\n')
             return
         if not self._found_start_time or not self._found_end_time:
             sys.stdout.write('No valid digests found in range\n')
         else:
-            sys.stdout.write('Results found for %s to %s:\n'
-                             % (format_display_date(self._found_start_time),
-                                format_display_date(self._found_end_time)))
+            sys.stdout.write(f'Results found for {format_display_date(self._found_start_time)} to {format_display_date(self._found_end_time)}:\n')
         self._write_ratio(self._valid_digests, self._invalid_digests, 'digest')
         self._write_ratio(self._valid_logs, self._invalid_logs, 'log')
         sys.stdout.write('\n')
@@ -845,13 +830,11 @@ def _write_ratio(self, valid, invalid, name):
 
     def _on_missing_digest(self, bucket, last_key, **kwargs):
         self._invalid_digests += 1
-        self._write_status('Digest file\ts3://%s/%s\tINVALID: not found'
-                           % (bucket, last_key), True)
+        self._write_status(f'Digest file\ts3://{bucket}/{last_key}\tINVALID: not found', True)
 
     def _on_digest_gap(self, **kwargs):
         self._write_status(
-            'No log files were delivered by CloudTrail between %s and %s'
-            % (format_display_date(kwargs['next_end_date']),
+            'No log files were delivered by CloudTrail between {} and {}'.format(format_display_date(kwargs['next_end_date']),
                format_display_date(kwargs['last_start_date'])), True)
 
     def _on_invalid_digest(self, message, **kwargs):
@@ -861,17 +844,14 @@ def _on_invalid_digest(self, message, **kwargs):
     def _on_invalid_log_format(self, log_data):
         self._invalid_logs += 1
         self._write_status(
-            ('Log file\ts3://%s/%s\tINVALID: invalid format'
-             % (log_data['s3Bucket'], log_data['s3Object'])), True)
+            ('Log file\ts3://{}/{}\tINVALID: invalid format'.format(log_data['s3Bucket'], log_data['s3Object'])), True)
 
     def _on_log_invalid(self, log_data):
         self._invalid_logs += 1
         self._write_status(
-            "Log file\ts3://%s/%s\tINVALID: hash value doesn't match"
-            % (log_data['s3Bucket'], log_data['s3Object']), True)
+            "Log file\ts3://{}/{}\tINVALID: hash value doesn't match".format(log_data['s3Bucket'], log_data['s3Object']), True)
 
     def _on_missing_log(self, log_data):
         self._invalid_logs += 1
         self._write_status(
-            'Log file\ts3://%s/%s\tINVALID: not found'
-            % (log_data['s3Bucket'], log_data['s3Object']), True)
+            'Log file\ts3://{}/{}\tINVALID: not found'.format(log_data['s3Bucket'], log_data['s3Object']), True)
diff --git a/awscli/customizations/configservice/getstatus.py b/awscli/customizations/configservice/getstatus.py
index d3a2dd8ce2e9..fe01925065b0 100644
--- a/awscli/customizations/configservice/getstatus.py
+++ b/awscli/customizations/configservice/getstatus.py
@@ -30,7 +30,7 @@ class GetStatusCommand(BasicCommand):
 
     def __init__(self, session):
         self._config_client = None
-        super(GetStatusCommand, self).__init__(session)
+        super().__init__(session)
 
     def _run_main(self, parsed_args, parsed_globals):
         self._setup_client(parsed_globals)
@@ -57,12 +57,12 @@ def _check_configuration_recorders(self):
     def _check_configure_recorder_status(self, configuration_recorder):
         # Get the name of the recorder and print it out.
         name = configuration_recorder['name']
-        sys.stdout.write('name: %s\n' % name)
+        sys.stdout.write(f'name: {name}\n')
 
         # Get the recording status and print it out.
         recording = configuration_recorder['recording']
         recording_map = {False: 'OFF', True: 'ON'}
-        sys.stdout.write('recorder: %s\n' % recording_map[recording])
+        sys.stdout.write(f'recorder: {recording_map[recording]}\n')
 
         # If the recorder is on, get the last status and print it out.
         if recording:
@@ -78,7 +78,7 @@ def _check_delivery_channels(self):
     def _check_delivery_channel_status(self, delivery_channel):
         # Get the name of the delivery channel and print it out.
         name = delivery_channel['name']
-        sys.stdout.write('name: %s\n' % name)
+        sys.stdout.write(f'name: {name}\n')
 
         # Obtain the various delivery statuses.
         stream_delivery = delivery_channel['configStreamDeliveryInfo']
@@ -95,7 +95,7 @@ def _check_delivery_channel_status(self, delivery_channel):
 
     def _check_last_status(self, status, status_name=''):
         last_status = status['lastStatus']
-        sys.stdout.write('last %sstatus: %s\n' % (status_name, last_status))
+        sys.stdout.write(f'last {status_name}status: {last_status}\n')
         if last_status == "FAILURE":
-            sys.stdout.write('error code: %s\n' % status['lastErrorCode'])
-            sys.stdout.write('message: %s\n' % status['lastErrorMessage'])
+            sys.stdout.write('error code: {}\n'.format(status['lastErrorCode']))
+            sys.stdout.write('message: {}\n'.format(status['lastErrorMessage']))
diff --git a/awscli/customizations/configservice/subscribe.py b/awscli/customizations/configservice/subscribe.py
index 0a3c1b2def31..d1c62af6a3ba 100644
--- a/awscli/customizations/configservice/subscribe.py
+++ b/awscli/customizations/configservice/subscribe.py
@@ -59,7 +59,7 @@ def __init__(self, session):
         self._s3_client = None
         self._sns_client = None
         self._config_client = None
-        super(SubscribeCommand, self).__init__(session)
+        super().__init__(session)
 
     def _run_main(self, parsed_args, parsed_globals):
         # Setup the necessary all of the necessary clients.
@@ -139,9 +139,9 @@ def prepare_bucket(self, s3_path):
         bucket_exists = self._check_bucket_exists(bucket)
         if not bucket_exists:
             self._create_bucket(bucket)
-            sys.stdout.write('Using new S3 bucket: %s\n' % bucket)
+            sys.stdout.write(f'Using new S3 bucket: {bucket}\n')
         else:
-            sys.stdout.write('Using existing S3 bucket: %s\n' % bucket)
+            sys.stdout.write(f'Using existing S3 bucket: {bucket}\n')
         return bucket, key
 
     def _check_bucket_exists(self, bucket):
@@ -168,9 +168,9 @@ def prepare_topic(self, sns_topic):
         if not self._check_is_arn(sns_topic):
             response = self._sns_client.create_topic(Name=sns_topic)
             sns_topic_arn = response['TopicArn']
-            sys.stdout.write('Using new SNS topic: %s\n' % sns_topic_arn)
+            sys.stdout.write(f'Using new SNS topic: {sns_topic_arn}\n')
         else:
-            sys.stdout.write('Using existing SNS topic: %s\n' % sns_topic_arn)
+            sys.stdout.write(f'Using existing SNS topic: {sns_topic_arn}\n')
         return sns_topic_arn
 
     def _check_is_arn(self, sns_topic):
diff --git a/awscli/customizations/configure/configure.py b/awscli/customizations/configure/configure.py
index aa8fc88ea9fd..6f7770cf618d 100644
--- a/awscli/customizations/configure/configure.py
+++ b/awscli/customizations/configure/configure.py
@@ -45,7 +45,7 @@ class InteractivePrompter:
     def get_value(self, current_value, config_name, prompt_text=''):
         if config_name in ('aws_access_key_id', 'aws_secret_access_key'):
             current_value = mask_value(current_value)
-        response = compat_input("%s [%s]: " % (prompt_text, current_value))
+        response = compat_input(f"{prompt_text} [{current_value}]: ")
         if not response:
             # If the user hits enter, we return a value of None
             # instead of an empty string.  That way we can determine
@@ -98,7 +98,7 @@ class ConfigureCommand(BasicCommand):
     ]
 
     def __init__(self, session, prompter=None, config_writer=None):
-        super(ConfigureCommand, self).__init__(session)
+        super().__init__(session)
         if prompter is None:
             prompter = InteractivePrompter()
         self._prompter = prompter
diff --git a/awscli/customizations/configure/exportcreds.py b/awscli/customizations/configure/exportcreds.py
index 7082f0c5b8ba..bf516865390e 100644
--- a/awscli/customizations/configure/exportcreds.py
+++ b/awscli/customizations/configure/exportcreds.py
@@ -194,7 +194,7 @@ class ConfigureExportCredentialsCommand(BasicCommand):
     _MAX_RECURSION = 4
 
     def __init__(self, session, out_stream=None, error_stream=None, env=None):
-        super(ConfigureExportCredentialsCommand, self).__init__(session)
+        super().__init__(session)
         if out_stream is None:
             out_stream = sys.stdout
         if error_stream is None:
diff --git a/awscli/customizations/configure/get.py b/awscli/customizations/configure/get.py
index 624b8768d793..306604bcf3b4 100644
--- a/awscli/customizations/configure/get.py
+++ b/awscli/customizations/configure/get.py
@@ -34,7 +34,7 @@ class ConfigureGetCommand(BasicCommand):
     ]
 
     def __init__(self, session, stream=None, error_stream=None):
-        super(ConfigureGetCommand, self).__init__(session)
+        super().__init__(session)
         if stream is None:
             stream = sys.stdout
         if error_stream is None:
@@ -53,7 +53,7 @@ def _run_main(self, args, parsed_globals):
         else:
             value = self._get_dotted_config_value(varname)
 
-        LOG.debug('Config value retrieved: %s' % value)
+        LOG.debug(f'Config value retrieved: {value}')
 
         if isinstance(value, str):
             self._stream.write(value)
@@ -63,8 +63,8 @@ def _run_main(self, args, parsed_globals):
             # TODO: add support for this. We would need to print it off in
             # the same format as the config file.
             self._error_stream.write(
-                'varname (%s) must reference a value, not a section or '
-                'sub-section.' % varname
+                f'varname ({varname}) must reference a value, not a section or '
+                'sub-section.'
             )
             return 1
         else:
diff --git a/awscli/customizations/configure/importer.py b/awscli/customizations/configure/importer.py
index 2aeb4627c787..2a35a264771f 100644
--- a/awscli/customizations/configure/importer.py
+++ b/awscli/customizations/configure/importer.py
@@ -60,7 +60,7 @@ class ConfigureImportCommand(BasicCommand):
 
     def __init__(self, session, csv_parser=None, importer=None,
                  out_stream=None):
-        super(ConfigureImportCommand, self).__init__(session)
+        super().__init__(session)
         if csv_parser is None:
             csv_parser = CSVCredentialParser()
         self._csv_parser = csv_parser
@@ -86,7 +86,7 @@ def _import_csv(self, contents):
                 credential, config_path,
                 profile_prefix=self._profile_prefix,
             )
-        import_msg = 'Successfully imported %s profile(s)\n' % len(credentials)
+        import_msg = f'Successfully imported {len(credentials)} profile(s)\n'
         uni_print(import_msg, out_file=self._out_stream)
 
     def _run_main(self, parsed_args, parsed_globals):
diff --git a/awscli/customizations/configure/list.py b/awscli/customizations/configure/list.py
index c1f0f342e058..a1c073b5a961 100644
--- a/awscli/customizations/configure/list.py
+++ b/awscli/customizations/configure/list.py
@@ -51,7 +51,7 @@ class ConfigureListCommand(BasicCommand):
     )
 
     def __init__(self, session, stream=None):
-        super(ConfigureListCommand, self).__init__(session)
+        super().__init__(session)
         if stream is None:
             stream = sys.stdout
         self._stream = stream
diff --git a/awscli/customizations/configure/listprofiles.py b/awscli/customizations/configure/listprofiles.py
index 411fb858ad8c..9d1be3926c5e 100644
--- a/awscli/customizations/configure/listprofiles.py
+++ b/awscli/customizations/configure/listprofiles.py
@@ -26,7 +26,7 @@ class ListProfilesCommand(BasicCommand):
     )
 
     def __init__(self, session, out_stream=None):
-        super(ListProfilesCommand, self).__init__(session)
+        super().__init__(session)
 
         if out_stream is None:
             out_stream = sys.stdout
@@ -34,5 +34,5 @@ def __init__(self, session, out_stream=None):
 
     def _run_main(self, parsed_args, parsed_globals):
         for profile in self._session.available_profiles:
-            uni_print('%s\n' % profile, out_file=self._out_stream)
+            uni_print(f'{profile}\n', out_file=self._out_stream)
         return 0
diff --git a/awscli/customizations/configure/set.py b/awscli/customizations/configure/set.py
index c17f38d955a3..ce2df90236be 100644
--- a/awscli/customizations/configure/set.py
+++ b/awscli/customizations/configure/set.py
@@ -41,7 +41,7 @@ class ConfigureSetCommand(BasicCommand):
                             'aws_session_token']
 
     def __init__(self, session, config_writer=None):
-        super(ConfigureSetCommand, self).__init__(session)
+        super().__init__(session)
         if config_writer is None:
             config_writer = ConfigFileWriter()
         self._config_writer = config_writer
diff --git a/awscli/customizations/configure/sso.py b/awscli/customizations/configure/sso.py
index d10e9a4703ee..251a507b234b 100644
--- a/awscli/customizations/configure/sso.py
+++ b/awscli/customizations/configure/sso.py
@@ -64,7 +64,7 @@
 
 class ValidatorWithDefault(Validator):
     def __init__(self, default=None):
-        super(ValidatorWithDefault, self).__init__()
+        super().__init__()
         self._default = default
 
     def _raise_validation_error(self, document, message):
@@ -326,7 +326,7 @@ def _get_previously_used_scopes_to_sso_sessions(self):
 
 class BaseSSOConfigurationCommand(BaseSSOCommand):
     def __init__(self, session, prompter=None, config_writer=None):
-        super(BaseSSOConfigurationCommand, self).__init__(session)
+        super().__init__(session)
         if prompter is None:
             prompter = PTKPrompt()
         self._prompter = prompter
@@ -370,7 +370,7 @@ class ConfigureSSOCommand(BaseSSOConfigurationCommand):
 
     def __init__(self, session, prompter=None, selector=None,
                  config_writer=None, sso_token_cache=None, sso_login=None):
-        super(ConfigureSSOCommand, self).__init__(
+        super().__init__(
             session, prompter=prompter, config_writer=config_writer)
         if selector is None:
             selector = select_menu
diff --git a/awscli/customizations/configure/writer.py b/awscli/customizations/configure/writer.py
index 077196c085e9..b7185c2de1cd 100644
--- a/awscli/customizations/configure/writer.py
+++ b/awscli/customizations/configure/writer.py
@@ -92,7 +92,7 @@ def _write_new_section(self, section_name, new_values, config_filename):
         with open(config_filename, 'a') as f:
             if needs_newline:
                 f.write('\n')
-            f.write('[%s]\n' % section_name)
+            f.write(f'[{section_name}]\n')
             contents = []
             self._insert_new_values(line_number=0,
                                     contents=contents,
@@ -143,7 +143,7 @@ def _update_section_contents(self, contents, section_name, new_values):
                     # out now.
                     if not isinstance(new_values[key_name], dict):
                         option_value = new_values[key_name]
-                        new_line = '%s = %s\n' % (key_name, option_value)
+                        new_line = f'{key_name} = {option_value}\n'
                         contents[j] = new_line
                         del new_values[key_name]
                     else:
@@ -171,7 +171,7 @@ def _update_subattributes(self, index, contents, values, starting_indent):
                 key_name = match.group(1).strip()
                 if key_name in values:
                     option_value = values[key_name]
-                    new_line = '%s%s = %s\n' % (' ' * current_indent,
+                    new_line = '{}{} = {}\n'.format(' ' * current_indent,
                                                 key_name, option_value)
                     contents[i] = new_line
                     del values[key_name]
@@ -192,20 +192,19 @@ def _insert_new_values(self, line_number, contents, new_values, indent=''):
         for key, value in list(new_values.items()):
             if isinstance(value, dict):
                 subindent = indent + '    '
-                new_contents.append('%s%s =\n' % (indent, key))
+                new_contents.append(f'{indent}{key} =\n')
                 for subkey, subval in list(value.items()):
-                    new_contents.append('%s%s = %s\n' % (subindent, subkey,
-                                                         subval))
+                    new_contents.append(f'{subindent}{subkey} = {subval}\n')
             else:
-                new_contents.append('%s%s = %s\n' % (indent, key, value))
+                new_contents.append(f'{indent}{key} = {value}\n')
             del new_values[key]
         contents.insert(line_number + 1, ''.join(new_contents))
 
     def _matches_section(self, match, section_name):
         parts = section_name.split(' ')
-        unquoted_match = match.group(0) == '[%s]' % section_name
+        unquoted_match = match.group(0) == f'[{section_name}]'
         if len(parts) > 1:
-            quoted_match = match.group(0) == '[%s "%s"]' % (
+            quoted_match = match.group(0) == '[{} "{}"]'.format(
                 parts[0], ' '.join(parts[1:]))
             return unquoted_match or quoted_match
         return unquoted_match