BAEL-3925 - How to call Python from Java? (#9277)
* BAEL-3491 - Check for null before calling parse in the Double.parseDouble * BAEL-3491 - Check for null before calling parse in the Double.parseDouble - Return to indentation with spaces. * BAEL-3854 - Pattern Matching for instanceof in Java 14 * BAEL-3854 - Pattern Matching for instanceof in Java 14 - add unit test * BAEL-3868 - Fix the integrations tests in mocks * BAEL-3925 - How to call Python from Java Co-authored-by: Jonathan Cook <jcook@sciops.esa.int>
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Jonathan Cook
GitHub
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## Java Python Interop
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This module contains articles about Java and Python interoperability.
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### Relevant Articles:
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<?xml version="1.0" encoding="UTF-8" ?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<artifactId>java-python-interop</artifactId>
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<version>0.0.1-SNAPSHOT</version>
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<name>java-python-interop</name>
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<parent>
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<groupId>com.baeldung</groupId>
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<artifactId>parent-modules</artifactId>
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<version>1.0.0-SNAPSHOT</version>
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</parent>
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<dependencies>
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<dependency>
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<groupId>org.python</groupId>
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<artifactId>jython-slim</artifactId>
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<version>${jython.version}</version>
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</dependency>
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<dependency>
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<groupId>org.apache.commons</groupId>
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<artifactId>commons-exec</artifactId>
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<version>${commons-exec.version}</version>
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</dependency>
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<dependency>
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<groupId>org.assertj</groupId>
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<artifactId>assertj-core</artifactId>
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<version>${assertj.version}</version>
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<scope>test</scope>
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</dependency>
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</dependencies>
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<build>
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<finalName>java-python-interop</finalName>
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<resources>
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<resource>
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<directory>src/main/resources</directory>
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<filtering>true</filtering>
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</resource>
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<resource>
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<directory>src/test/resources</directory>
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<filtering>true</filtering>
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</resource>
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</resources>
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</build>
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<properties>
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<jython.version>2.7.2</jython.version>
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<commons-exec.version>1.3</commons-exec.version>
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<assertj.version>3.6.1</assertj.version>
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</properties>
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</project>
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package com.baeldung.python.interop;
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import java.util.List;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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import javax.script.ScriptEngineFactory;
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import javax.script.ScriptEngineManager;
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public class ScriptEngineManagerUtils {
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private static final Logger LOGGER = LoggerFactory.getLogger(ScriptEngineManagerUtils.class);
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private ScriptEngineManagerUtils() {
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}
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public static void listEngines() {
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ScriptEngineManager manager = new ScriptEngineManager();
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List<ScriptEngineFactory> engines = manager.getEngineFactories();
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for (ScriptEngineFactory engine : engines) {
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LOGGER.info("Engine name: {}", engine.getEngineName());
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LOGGER.info("Version: {}", engine.getEngineVersion());
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LOGGER.info("Language: {}", engine.getLanguageName());
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LOGGER.info("Short Names:");
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for (String names : engine.getNames()) {
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LOGGER.info(names);
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}
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}
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}
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}
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<?xml version="1.0" encoding="UTF-8"?>
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<configuration>
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<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
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<encoder>
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<pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
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</pattern>
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</encoder>
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</appender>
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<root level="INFO">
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<appender-ref ref="STDOUT" />
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</root>
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</configuration>
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package com.baeldung.python.interop;
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import static org.hamcrest.Matchers.containsString;
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import static org.hamcrest.Matchers.empty;
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import static org.hamcrest.Matchers.hasItem;
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import static org.hamcrest.Matchers.is;
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import static org.hamcrest.Matchers.not;
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import static org.junit.Assert.assertEquals;
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import static org.junit.Assert.assertThat;
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import java.io.BufferedReader;
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import java.io.ByteArrayOutputStream;
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import java.io.File;
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import java.io.FileReader;
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import java.io.IOException;
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import java.io.InputStream;
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import java.io.InputStreamReader;
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import java.io.StringWriter;
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import java.util.List;
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import java.util.stream.Collectors;
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import javax.script.ScriptContext;
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import javax.script.ScriptEngine;
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import javax.script.ScriptEngineManager;
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import javax.script.SimpleScriptContext;
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import org.apache.commons.exec.CommandLine;
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import org.apache.commons.exec.DefaultExecutor;
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import org.apache.commons.exec.ExecuteException;
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import org.apache.commons.exec.PumpStreamHandler;
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import org.junit.Rule;
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import org.junit.Test;
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import org.junit.rules.ExpectedException;
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import org.python.core.PyException;
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import org.python.core.PyObject;
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import org.python.util.PythonInterpreter;
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public class JavaPythonInteropUnitTest {
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@Rule
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public ExpectedException thrown = ExpectedException.none();
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@Test
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public void givenPythonScript_whenPythonProcessInvoked_thenSuccess() throws Exception {
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ProcessBuilder processBuilder = new ProcessBuilder("python", resolvePythonScriptPath("hello.py"));
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processBuilder.redirectErrorStream(true);
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Process process = processBuilder.start();
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List<String> results = readProcessOutput(process.getInputStream());
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assertThat("Results should not be empty", results, is(not(empty())));
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assertThat("Results should contain output of script: ", results, hasItem(containsString("Hello Baeldung Readers!!")));
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int exitCode = process.waitFor();
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assertEquals("No errors should be detected", 0, exitCode);
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}
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@Test
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public void givenPythonScriptEngineIsAvailable_whenScriptInvoked_thenOutputDisplayed() throws Exception {
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StringWriter output = new StringWriter();
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ScriptContext context = new SimpleScriptContext();
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context.setWriter(output);
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ScriptEngineManager manager = new ScriptEngineManager();
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ScriptEngine engine = manager.getEngineByName("python");
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engine.eval(new FileReader(resolvePythonScriptPath("hello.py")), context);
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assertEquals("Should contain script output: ", "Hello Baeldung Readers!!", output.toString()
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.trim());
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}
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@Test
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public void givenPythonInterpreter_whenPrintExecuted_thenOutputDisplayed() {
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try (PythonInterpreter pyInterp = new PythonInterpreter()) {
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StringWriter output = new StringWriter();
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pyInterp.setOut(output);
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pyInterp.exec("print('Hello Baeldung Readers!!')");
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assertEquals("Should contain script output: ", "Hello Baeldung Readers!!", output.toString()
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.trim());
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}
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}
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@Test
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public void givenPythonInterpreter_whenNumbersAdded_thenOutputDisplayed() {
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try (PythonInterpreter pyInterp = new PythonInterpreter()) {
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pyInterp.exec("x = 10+10");
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PyObject x = pyInterp.get("x");
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assertEquals("x: ", 20, x.asInt());
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}
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}
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@Test
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public void givenPythonInterpreter_whenErrorOccurs_thenExceptionIsThrown() {
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thrown.expect(PyException.class);
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thrown.expectMessage("ImportError: No module named syds");
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try (PythonInterpreter pyInterp = new PythonInterpreter()) {
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pyInterp.exec("import syds");
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}
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}
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@Test
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public void givenPythonScript_whenPythonProcessExecuted_thenSuccess() throws ExecuteException, IOException {
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String line = "python " + resolvePythonScriptPath("hello.py");
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CommandLine cmdLine = CommandLine.parse(line);
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ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
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PumpStreamHandler streamHandler = new PumpStreamHandler(outputStream);
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DefaultExecutor executor = new DefaultExecutor();
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executor.setStreamHandler(streamHandler);
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int exitCode = executor.execute(cmdLine);
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assertEquals("No errors should be detected", 0, exitCode);
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assertEquals("Should contain script output: ", "Hello Baeldung Readers!!", outputStream.toString()
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.trim());
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}
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private List<String> readProcessOutput(InputStream inputStream) throws IOException {
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try (BufferedReader output = new BufferedReader(new InputStreamReader(inputStream))) {
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return output.lines()
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.collect(Collectors.toList());
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}
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}
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private String resolvePythonScriptPath(String filename) {
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File file = new File("src/test/resources/" + filename);
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return file.getAbsolutePath();
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}
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}
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print("Hello Baeldung Readers!!")
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