Use list literal instead of list()

dict, tuple, and list literals are actually single instructions in the CPython virtual machine, so it's always faster and better form to use them over the type constructors.

Author: adamchainz

docs/getting_started/rules.md

@@ -71,7 +71,7 @@ class MyNewRule(CloudFormationLintRule):
     def match(self, cfn):
         """Basic Rule Matching"""
 
-        matches = list()
+        matches = []
 
         # Your Rule code goes here
 
@@ -208,7 +208,7 @@ The following snippet is a simple example on checking specific property values:
 ```python
 def check_value(self, value, path):
     """Check SecurityGroup descriptions"""
-    matches = list()
+    matches = []
     full_path = ('/'.join(str(x) for x in path))
 
     # Check max length
@@ -219,7 +219,7 @@ def check_value(self, value, path):
 def match(self, cfn):
     """Check SecurityGroup descriptions"""
 
-    matches = list()
+    matches = []
 
     resources = cfn.get_resources(['AWS::EC2::SecurityGroup'])
 

examples/rules/PropertiesTagsIncluded.py

@@ -31,7 +31,7 @@ def get_resources_with_tags(self, region):
         resourcespecs = cfnlint.helpers.RESOURCE_SPECS[region]
         resourcetypes = resourcespecs['ResourceTypes']
 
-        matches = list()
+        matches = []
         for resourcetype, resourceobj in resourcetypes.items():
             propertiesobj = resourceobj.get('Properties')
             if propertiesobj:
@@ -43,7 +43,7 @@ def get_resources_with_tags(self, region):
     def match(self, cfn):
         """Check Tags for required keys"""
 
-        matches = list()
+        matches = []
 
         all_tags = cfn.search_deep_keys('Tags')
         all_tags = [x for x in all_tags if x[0] == 'Resources']

examples/rules/PropertiesTagsRequired.py

@@ -28,7 +28,7 @@ class PropertiesTagsRequired(CloudFormationLintRule):
     def match(self, cfn):
         """Check Tags for required keys"""
 
-        matches = list()
+        matches = []
 
         required_tags = ['CostCenter', 'ApplicationName']
 

src/cfnlint/__init__.py

@@ -164,7 +164,7 @@ def is_rule_enabled(self, rule_id):
 
     def resource_property(self, filename, cfn, path, properties, resource_type, property_type):
         """Run loops in resource checks for embedded properties"""
-        matches = list()
+        matches = []
         property_spec = cfnlint.helpers.RESOURCE_SPECS['us-east-1'].get('PropertyTypes')
         if property_type == 'Tag':
             property_spec_name = 'Tag'
@@ -221,7 +221,7 @@ def resource_property(self, filename, cfn, path, properties, resource_type, prop
 
     def run_resource(self, filename, cfn, resource_type, resource_properties, path):
         """Run loops in resource checks for embedded properties"""
-        matches = list()
+        matches = []
         resource_spec = cfnlint.helpers.RESOURCE_SPECS['us-east-1'].get('ResourceTypes')
         if resource_properties and resource_type in resource_spec:
             resource_spec_properties = resource_spec.get(resource_type, {}).get('Properties')
@@ -259,7 +259,7 @@ def run_resource(self, filename, cfn, resource_type, resource_properties, path):
 
     def run(self, filename, cfn):
         """Run rules"""
-        matches = list()
+        matches = []
         for rule in self.rules:
             try:
                 matches.extend(rule.matchall(filename, cfn))
@@ -423,7 +423,7 @@ def get_mappings(self):
     def get_resource_names(self):
         """Get all the Resource Names"""
         LOGGER.debug('Get the names of all resources from template...')
-        results = list()
+        results = []
         resources = self.template.get('Resources', {})
         if isinstance(resources, dict):
             for resourcename, _ in resources.items():
@@ -434,7 +434,7 @@ def get_resource_names(self):
     def get_parameter_names(self):
         """Get all Parameter Names"""
         LOGGER.debug('Get names of all parameters from template...')
-        results = list()
+        results = []
         parameters = self.template.get('Parameters', {})
         if isinstance(parameters, dict):
             for parametername, _ in parameters.items():
@@ -524,15 +524,15 @@ def _get_sub_resource_properties(self, keys, properties, path):
                     if results:
                         return results
         elif isinstance(properties, list):
-            matches = list()
+            matches = []
             for index, item in enumerate(properties):
                 results = None
                 if isinstance(item, dict):
                     if len(item) == 1:
                         for sub_key, sub_value in item.items():
                             if sub_key in cfnlint.helpers.CONDITION_FUNCTIONS:
                                 cond_values = self.get_condition_values(sub_value)
-                                results = list()
+                                results = []
                                 for cond_value in cond_values:
                                     result_path = path[:] + [index, sub_key] + cond_value['Path']
                                     results.extend(
@@ -551,12 +551,12 @@ def _get_sub_resource_properties(self, keys, properties, path):
                     matches.extend(results)
             return matches
 
-        return list()
+        return []
 
     def get_resource_properties(self, keys):
         """Filter keys of template"""
         LOGGER.debug('Get Properties from a resource: %s', keys)
-        matches = list()
+        matches = []
         resourcetype = keys.pop(0)
         for resource_name, resource_value in self.get_resources(resourcetype).items():
             path = ['Resources', resource_name, 'Properties']
@@ -570,7 +570,7 @@ def get_resource_properties(self, keys):
     # pylint: disable=dangerous-default-value
     def _search_deep_keys(self, searchText, cfndict, path):
         """Search deep for keys and get their values"""
-        keys = list()
+        keys = []
         if isinstance(cfndict, dict):
             for key in cfndict:
                 pathprop = path[:]
@@ -606,7 +606,7 @@ def search_deep_keys(self, searchText):
     def get_condition_values(self, template, path=[]):
         """Evaluates conditions and brings back the values"""
         LOGGER.debug('Get condition values...')
-        matches = list()
+        matches = []
         if not isinstance(template, list):
             return matches
         if not len(template) == 3:
@@ -656,7 +656,7 @@ def get_values(self, obj, key, path=[]):
 
         """
         LOGGER.debug('Get the value for key %s in %s', key, obj)
-        matches = list()
+        matches = []
 
         if not isinstance(obj, dict):
             return None
@@ -774,7 +774,7 @@ def check_resource_property(self, resource_type, resource_property,
                                 check_join=None, check_sub=None, **kwargs):
         """ Check Resource Properties """
         LOGGER.debug('Check property %s for %s', resource_property, resource_type)
-        matches = list()
+        matches = []
         resources = self.get_resources(resource_type=resource_type)
         for resource_name, resource_object in resources.items():
             properties = resource_object.get('Properties', {})
@@ -800,7 +800,7 @@ def check_value(self, obj, key, path,
             Check the value
         """
         LOGGER.debug('Check value %s for %s', key, obj)
-        matches = list()
+        matches = []
         values_obj = self.get_values(obj=obj, key=key)
         new_path = path[:] + [key]
         if not values_obj:
@@ -882,14 +882,14 @@ def transform(self):
     def run(self):
         """Run rules"""
         LOGGER.debug('Run scan of template...')
-        matches = list()
+        matches = []
         if self.cfn.template is not None:
             matches.extend(
                 self.rules.run(
                     self.filename, self.cfn))
 
         # uniq the list of incidents
-        return_matches = list()
+        return_matches = []
         for _, match in enumerate(matches):
             if not any(match == u for u in return_matches):
                 return_matches.append(match)

src/cfnlint/core.py

@@ -286,7 +286,7 @@ def run_checks(filename, template, rules, regions):
                 LOGGER.error('Supported regions are %s', REGIONS)
                 exit(32)
 
-    matches = list()
+    matches = []
 
     runner = cfnlint.Runner(rules, filename, template, regions)
     matches.extend(runner.transform())

src/cfnlint/rules/conditions/Configuration.py

@@ -37,7 +37,7 @@ class Configuration(CloudFormationLintRule):
     def match(self, cfn):
         """Check CloudFormation Conditions"""
 
-        matches = list()
+        matches = []
 
         conditions = cfn.template.get('Conditions', {})
         if conditions:

src/cfnlint/rules/conditions/Used.py

@@ -30,8 +30,8 @@ class Used(CloudFormationLintRule):
     def match(self, cfn):
         """Check CloudFormation Conditions"""
 
-        matches = list()
-        ref_conditions = list()
+        matches = []
+        ref_conditions = []
 
         conditions = cfn.template.get('Conditions', {})
         if conditions:

src/cfnlint/rules/functions/Base64.py

@@ -30,7 +30,7 @@ class Base64(CloudFormationLintRule):
     def match(self, cfn):
         """Check CloudFormation Base64"""
 
-        matches = list()
+        matches = []
 
         base64_objs = cfn.search_deep_keys('Fn::Base64')
         for base64_obj in base64_objs:

src/cfnlint/rules/functions/Cidr.py

@@ -31,7 +31,7 @@ class Cidr(CloudFormationLintRule):
 
     def check_parameter_count(self, cfn, parameter_name):
         """Check Count Parameter if used"""
-        matches = list()
+        matches = []
         parameter_obj = cfn.get_parameters().get(parameter_name, {})
         if parameter_obj:
             tree = ['Parameters', parameter_name]
@@ -56,7 +56,7 @@ def check_parameter_count(self, cfn, parameter_name):
 
     def check_parameter_size_mask(self, cfn, parameter_name):
         """Check SizeMask Parameter if used"""
-        matches = list()
+        matches = []
         parameter_obj = cfn.get_parameters().get(parameter_name, {})
         if parameter_obj:
             tree = ['Parameters', parameter_name]
@@ -84,7 +84,7 @@ def check_parameter_size_mask(self, cfn, parameter_name):
     def match(self, cfn):
         """Check CloudFormation Cidr"""
 
-        matches = list()
+        matches = []
 
         cidr_objs = cfn.search_deep_keys('Fn::Cidr')
 

src/cfnlint/rules/functions/DynamicReferenceSecureString.py

@@ -57,7 +57,7 @@ def __init__(self, ):
 
     def check_dyn_ref_value(self, value, path):
         """Chec item type"""
-        matches = list()
+        matches = []
 
         if isinstance(value, six.string_types):
             if re.match(cfnlint.helpers.REGEX_DYN_REF_SSM_SECURE, value):
@@ -69,7 +69,7 @@ def check_dyn_ref_value(self, value, path):
 
     def check_value(self, value, path, **kwargs):
         """Check Value"""
-        matches = list()
+        matches = []
         item_type = kwargs.get('item_type', {})
         if item_type in ['Map']:
             if isinstance(value, dict):
@@ -85,7 +85,7 @@ def check_value(self, value, path, **kwargs):
     # Need to disable for the function to work
     def check_sub(self, value, path, **kwargs):
         """Check Sub Function Dynamic References"""
-        matches = list()
+        matches = []
         if isinstance(value, list):
             if isinstance(value[0], six.string_types):
                 matches.extend(self.check_dyn_ref_value(value[0], path[:] + [0]))
@@ -96,7 +96,7 @@ def check_sub(self, value, path, **kwargs):
 
     def check(self, cfn, properties, specs, property_type, path):
         """Check itself"""
-        matches = list()
+        matches = []
 
         for prop in properties:
             if prop in specs:
@@ -125,7 +125,7 @@ def check(self, cfn, properties, specs, property_type, path):
 
     def match_resource_sub_properties(self, properties, property_type, path, cfn):
         """Match for sub properties"""
-        matches = list()
+        matches = []
 
         property_specs = self.property_specs.get(property_type, {}).get('Properties', {})
         matches.extend(self.check(cfn, properties, property_specs, property_type, path))
@@ -134,7 +134,7 @@ def match_resource_sub_properties(self, properties, property_type, path, cfn):
 
     def match_resource_properties(self, properties, resource_type, path, cfn):
         """Check CloudFormation Properties"""
-        matches = list()
+        matches = []
         resource_specs = self.resource_specs.get(resource_type, {}).get('Properties', {})
         matches.extend(self.check(cfn, properties, resource_specs, resource_type, path))