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SONARPY-3114 Rule S7621: AWS waiters should be used instead of custom polling loops (#427)
GitOrigin-RevId: 49d2035805ab3ef579efb5de7505b336ee27cf57
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‎python-checks/src/main/java/org/sonar/python/checks/AwsWaitersInsteadOfCustomPollingCheck.java‎

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/*
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* SonarQube Python Plugin
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* Copyright (C) 2011-2025 SonarSource SA
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* mailto:info AT sonarsource DOT com
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the Sonar Source-Available License Version 1, as published by SonarSource SA.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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* See the Sonar Source-Available License for more details.
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*
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* You should have received a copy of the Sonar Source-Available License
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* along with this program; if not, see https://sonarsource.com/license/ssal/
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*/
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package org.sonar.python.checks;
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import java.util.Set;
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import org.sonar.check.Rule;
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import org.sonar.plugins.python.api.PythonSubscriptionCheck;
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import org.sonar.plugins.python.api.SubscriptionContext;
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import org.sonar.plugins.python.api.tree.CallExpression;
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import org.sonar.plugins.python.api.tree.FunctionDef;
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import org.sonar.plugins.python.api.tree.Tree;
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import org.sonar.plugins.python.api.tree.WhileStatement;
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import org.sonar.python.checks.utils.AwsLambdaChecksUtils;
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import org.sonar.python.checks.utils.Expressions;
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import org.sonar.python.tree.TreeUtils;
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import org.sonar.python.types.v2.TypeCheckMap;
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@Rule(key = "S7621")
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public class AwsWaitersInsteadOfCustomPollingCheck extends PythonSubscriptionCheck {
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private static final Set<String> NON_WAITERS_BOTO3_METHODS = Set.of(
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// EC2
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"botocore.client.BaseClient.describe_instances",
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"botocore.client.BaseClient.describe_instance_status",
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"botocore.client.BaseClient.describe_volumes",
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"botocore.client.BaseClient.describe_snapshots",
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"botocore.client.BaseClient.describe_images",
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"botocore.client.BaseClient.describe_vpcs",
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"botocore.client.BaseClient.describe_subnets",
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"botocore.client.BaseClient.describe_nat_gateways",
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"botocore.client.BaseClient.describe_key_pairs",
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"botocore.client.BaseClient.get_password_data",
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// S3
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"botocore.client.BaseClient.head_bucket",
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"botocore.client.BaseClient.head_object",
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// RDS
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"botocore.client.BaseClient.describe_db_instances",
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"botocore.client.BaseClient.describe_db_clusters",
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"botocore.client.BaseClient.describe_db_snapshots",
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// DynamoDB
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"botocore.client.BaseClient.describe_table",
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// ECS
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"botocore.client.BaseClient.describe_services",
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"botocore.client.BaseClient.describe_tasks",
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// EKS
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"botocore.client.BaseClient.describe_cluster",
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"botocore.client.BaseClient.describe_nodegroup",
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// CloudFormation
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"botocore.client.BaseClient.describe_stacks",
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"botocore.client.BaseClient.describe_change_set",
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// Lambda
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"botocore.client.BaseClient.get_function_configuration",
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"botocore.client.BaseClient.get_function"
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);
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private final TypeCheckMap<Boolean> nonWaitersBoto3MethodsTypeCheckMap = new TypeCheckMap<>();
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@Override
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public void initialize(Context context) {
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context.registerSyntaxNodeConsumer(Tree.Kind.FILE_INPUT, this::initializeCheck);
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context.registerSyntaxNodeConsumer(Tree.Kind.CALL_EXPR, this::check);
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}
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private void initializeCheck(SubscriptionContext ctx) {
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NON_WAITERS_BOTO3_METHODS.stream()
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.map(fqn -> ctx.typeChecker().typeCheckBuilder().isTypeWithFqn(fqn))
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.forEach(check -> nonWaitersBoto3MethodsTypeCheckMap.put(check, true));
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}
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private void check(SubscriptionContext ctx) {
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var callExpression = (CallExpression) ctx.syntaxNode();
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if (nonWaitersBoto3MethodsTypeCheckMap.containsForType(TreeUtils.inferSingleAssignedExpressionType(callExpression.callee()))
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&& TreeUtils.firstAncestorOfKind(callExpression, Tree.Kind.WHILE_STMT) instanceof WhileStatement whileStatement
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&& Expressions.isTruthy(whileStatement.condition())
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&& TreeUtils.firstAncestorOfKind(callExpression, Tree.Kind.FUNCDEF) instanceof FunctionDef functionDef
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&& AwsLambdaChecksUtils.isLambdaHandler(ctx, functionDef)
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) {
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ctx.addIssue(callExpression, "Use AWS waiters instead of custom polling loops.");
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}
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}
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}

‎python-checks/src/main/java/org/sonar/python/checks/OpenSourceCheckList.java‎

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AwsLambdaReservedEnvironmentVariableCheck.class,
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AwsLambdaReturnValueAreSerializableCheck.class,
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AwsMissingPaginationCheck.class,
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AwsWaitersInsteadOfCustomPollingCheck.class,
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BackslashInStringCheck.class,
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BackticksUsageCheck.class,
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BareRaiseInFinallyCheck.class,

‎python-checks/src/main/resources/org/sonar/l10n/py/rules/python/S7621.html‎

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<p>This rule raises an issue when custom polling loops are used instead of AWS waiters for checking resource states.</p>
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<h2>Why is this an issue?</h2>
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<p>When working with AWS resources that require time to reach a desired state, such as EC2 instances starting up, S3 buckets being created, or
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DynamoDB tables becoming available, developers often implement custom polling loops to check the resource status repeatedly. However, this approach is
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inefficient and error-prone. Custom polling requires manual handling of timing intervals, retry logic, error conditions, and timeout scenarios. It
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also tends to be verbose and duplicates logic that AWS already provides in a more robust form. AWS SDK provides waiters, which are purpose-built
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abstractions specifically designed to poll AWS resources until they reach a desired state. Waiters handle the complexities of polling automatically,
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including appropriate delays, exponential backoff, maximum wait times, and proper error handling.</p>
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<h3>What is the potential impact?</h3>
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<p>Custom polling implementations can lead to inefficient resource usage due to inappropriate polling intervals, increased complexity and maintenance
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overhead, potential race conditions and timing issues, and unreliable error handling that may cause application failures or infinite loops.</p>
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<h2>How to fix it</h2>
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<p>Replace custom polling loops with AWS waiters. Identify the AWS resource you need to wait for, then use the appropriate waiter method from the
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boto3 client. Waiters are available for most AWS services and common state transitions. Use the <code>get_waiter()</code> method on your boto3 client
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to obtain the waiter, then call <code>wait()</code> with the appropriate parameters.</p>
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<h3>Noncompliant code example</h3>
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<pre data-diff-id="1" data-diff-type="noncompliant">
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import boto3
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import time
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ec2_client = boto3.client('ec2', region_name='us-east-1')
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while True:
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response = ec2_client.describe_instance_status( # Noncompliant
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InstanceIds=[instance_id],
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IncludeAllInstances=True
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)
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instance_status = response['Statuses'][0]['InstanceStatus']['Status']
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if instance_status == 'ok':
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break
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time.sleep(10)
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</pre>
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<h3>Compliant solution</h3>
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<pre data-diff-id="1" data-diff-type="compliant">
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import boto3
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ec2_client = boto3.client('ec2', region_name='us-east-1')
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ec2_client.get_waiter('instance_status_ok').wait(
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InstanceIds=[instance_id],
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IncludeAllInstances=True
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)
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</pre>
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<h2>Resources</h2>
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<ul>
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<li> boto3 Documentation - <a href="https://boto3.amazonaws.com/v1/documentation/api/latest/guide/clients.html#waiters">Waiters</a> </li>
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<li> AWS Documentation - <a href="https://docs.aws.amazon.com/lambda/latest/dg/python-handler.html#python-handler-best-practices">AWS Lambda Python
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Handler Best Practices</a> </li>
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</ul>
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‎python-checks/src/main/resources/org/sonar/l10n/py/rules/python/S7621.json‎

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{
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"title": "AWS waiters should be used instead of custom polling loops",
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"type": "CODE_SMELL",
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"status": "ready",
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"remediation": {
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"func": "Constant\/Issue",
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"constantCost": "5min"
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},
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"tags": [
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"aws"
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],
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"defaultSeverity": "Major",
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"ruleSpecification": "RSPEC-S7621",
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"sqKey": "S7621",
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"scope": "Main",
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"quickfix": "infeasible",
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"code": {
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"impacts": {
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"MAINTAINABILITY": "LOW",
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"RELIABILITY": "MEDIUM"
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},
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"attribute": "EFFICIENT"
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}
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}

‎python-checks/src/main/resources/org/sonar/l10n/py/rules/python/Sonar_way_profile.json‎

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"S7516",
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"S7517",
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"S7519",
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"S7617",
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"S7613",
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"S7617",
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"S7621",
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"S7622",
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"S7632"
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]

‎python-checks/src/test/java/org/sonar/python/checks/AwsWaitersInsteadOfCustomPollingCheckTest.java‎

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/*
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* SonarQube Python Plugin
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* Copyright (C) 2011-2025 SonarSource SA
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* mailto:info AT sonarsource DOT com
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the Sonar Source-Available License Version 1, as published by SonarSource SA.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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* See the Sonar Source-Available License for more details.
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*
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* You should have received a copy of the Sonar Source-Available License
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* along with this program; if not, see https://sonarsource.com/license/ssal/
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*/
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package org.sonar.python.checks;
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import org.junit.jupiter.api.Test;
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import org.sonar.python.checks.utils.PythonCheckVerifier;
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class AwsWaitersInsteadOfCustomPollingCheckTest {
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@Test
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void test() {
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PythonCheckVerifier.verify("src/test/resources/checks/awsWaitersInsteadOfCustomPolling.py", new AwsWaitersInsteadOfCustomPollingCheck());
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}
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}

‎python-checks/src/test/resources/checks/awsWaitersInsteadOfCustomPolling.py‎

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import boto3
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client = boto3.client('s3')
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def lambda_handler(event, context):
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while True:
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response = client.describe_instances() # Noncompliant
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while context:
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response = client.describe_instances() # OK
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response = client.describe_instances() # OK
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def not_a_lambda():
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while True:
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response = client.describe_instances() # OK
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response = client.describe_instances() # OK
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while a:
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response = client.describe_instances() # OK

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