ZEPPELIN-1287. No need to call print to display output in PythonInterpreter

python/src/main/java/org/apache/zeppelin/python/PythonInterpreter.java

@@ -134,10 +134,11 @@ public InterpreterResult interpret(String cmd, InterpreterContext contextInterpr
 
     InterpreterResult result;
     if (pythonErrorIn(output)) {
-      result = new InterpreterResult(Code.ERROR, output.replaceAll(">>>", "").trim());
+      result = new InterpreterResult(Code.ERROR, output);
     } else {
-      result = new InterpreterResult(Code.SUCCESS, output.replaceAll(">>>", "")
-          .replaceAll("\\.\\.\\.", "").trim());
+      // TODO(zjffdu), we should not do string replacement operation in the result, as it is
+      // possible that the output contains the kind of pattern itself, e.g. print("...")
+      result = new InterpreterResult(Code.SUCCESS, output.replaceAll("\\.\\.\\.", ""));
     }
     return result;
   }
@@ -265,4 +266,5 @@ private int findRandomOpenPortOnAllLocalInterfaces() {
   public int getMaxResult() {
     return maxResult;
   }
+
 }

python/src/main/java/org/apache/zeppelin/python/PythonProcess.java

@@ -21,24 +21,23 @@
 import org.slf4j.LoggerFactory;
 
 import java.io.BufferedReader;
-import java.io.BufferedWriter;
 import java.io.InputStream;
-import java.io.OutputStream;
 import java.io.IOException;
-import java.io.OutputStreamWriter;
 import java.io.InputStreamReader;
+import java.io.PrintWriter;
+import java.io.OutputStream;
 import java.lang.reflect.Field;
 
 /**
  * Object encapsulated interactive
  * Python process (REPL) used by python interpreter
  */
 public class PythonProcess {
-  Logger logger = LoggerFactory.getLogger(PythonProcess.class);
-
+  private static final Logger logger = LoggerFactory.getLogger(PythonProcess.class);
+  private static final String STATEMENT_END = "*!?flush reader!?*";
   InputStream stdout;
   OutputStream stdin;
-  BufferedWriter writer;
+  PrintWriter writer;
   BufferedReader reader;
   Process process;
 
@@ -56,7 +55,7 @@ public void open() throws IOException {
     process = builder.start();
     stdout = process.getInputStream();
     stdin = process.getOutputStream();
-    writer = new BufferedWriter(new OutputStreamWriter(stdin));
+    writer = new PrintWriter(stdin, true);
     reader = new BufferedReader(new InputStreamReader(stdout));
     try {
       pid = findPid();
@@ -85,22 +84,21 @@ public void interrupt() throws IOException {
   }
 
   public String sendAndGetResult(String cmd) throws IOException {
-    writer.write(cmd + "\n\n");
-    writer.write("print (\"*!?flush reader!?*\")\n\n");
-    writer.flush();
-
-    String output = "";
-    String line;
-    while (!(line = reader.readLine()).contains("*!?flush reader!?*")) {
+    writer.println(cmd);
+    writer.println();
+    writer.println("\"" + STATEMENT_END + "\"");
+    StringBuilder output = new StringBuilder();
+    String line = null;
+    while (!(line = reader.readLine()).contains(STATEMENT_END)) {
       logger.debug("Read line from python shell : " + line);
       if (line.equals("...")) {
         logger.warn("Syntax error ! ");
-        output += "Syntax error ! ";
+        output.append("Syntax error ! ");
         break;
       }
-      output += "\r" + line + "\n";
+      output.append(line + "\n");
     }
-    return output;
+    return output.toString();
   }
 
   private long findPid() throws NoSuchFieldException, IllegalAccessException {

python/src/main/resources/bootstrap.py

@@ -25,13 +25,13 @@
 except ImportError:
     import io as io
 
-sys.displayhook = lambda x: None
-
 def intHandler(signum, frame):  # Set the signal handler
     print ("Paragraph interrupted")
     raise KeyboardInterrupt()
 
 signal.signal(signal.SIGINT, intHandler)
+# set prompt as empty string so that java side don't need to remove the prompt.
+sys.ps1=""
 
 def help():
     print("""%html

python/src/test/java/org/apache/zeppelin/python/PythonInterpreterTest.java

@@ -115,7 +115,7 @@ public void testPy4jIsNotInstalled() {
    */
   @Test
   public void testPy4jInstalled() throws IOException, InterruptedException {
-    when(mockPythonProcess.sendAndGetResult(eq("\n\nimport py4j\n"))).thenReturn(">>>");
+    when(mockPythonProcess.sendAndGetResult(eq("\n\nimport py4j\n"))).thenReturn("");
 
     pythonInterpreter.open();
     Integer py4jPort = pythonInterpreter.getPy4jPort();
@@ -137,7 +137,7 @@ public void testPy4jInstalled() throws IOException, InterruptedException {
   @Test
   public void testClose() throws IOException, InterruptedException {
     //given: py4j is installed
-    when(mockPythonProcess.sendAndGetResult(eq("\n\nimport py4j\n"))).thenReturn(">>>");
+    when(mockPythonProcess.sendAndGetResult(eq("\n\nimport py4j\n"))).thenReturn("");
 
     pythonInterpreter.open();
     Integer py4jPort = pythonInterpreter.getPy4jPort();
@@ -210,11 +210,11 @@ private String answerFromPythonMock(InvocationOnMock invocationOnMock) {
       String output = "";
 
       for (int i = 0; i < lines.length; i++) {
-        output += ">>>" + lines[i];
+        output += lines[i];
       }
       return output;
     } else {
-      return ">>>";
+      return "";
     }
   }