Call Python 3.x functions in Java

Question

I want to call Python functions in Java. I know there is Jython, which comes with the PythonInterpreter for Java, but sadly it only supports Python 2.7.

For a better explanation of what I want to do. Let's say I have the following Python code in a given file:

@staticmethod
def my_first_function():
   print("Hi!")

@staticmethod
def my_second_function():
   print("Hi again!")

I want to be able to EXPLICITLY call functions like this in Java now:

PythonToJava pythonToJava = new PythonToJava("my/python/script/path");
pythonToJava.my_second_function(); 
pythonToJava.my_first_function();

How can I use/call a Python module/script/class/etc. in Java?

Try Py4J, it allows to define java interface to a python code py4j.org/… — nosklo
– nosklo, Commented Oct 9, 2018 at 14:25
I dont want to call Java functions in Python. I want to call Python functions in Java. — Faram
– Faram, Commented Oct 9, 2018 at 14:47
That's what the link I sent you is doing, please read - "... Py4J allows Python classes to implement Java interfaces so that the JVM can call back Python objects..." — nosklo
– nosklo, Commented Oct 9, 2018 at 15:34
Could you give me an example of how to implement that with my example code? — Faram
– Faram, Commented Oct 10, 2018 at 6:54
Sure, here's the example: py4j.org/… There is python code defining an interface and java code to call it. — nosklo
– nosklo, Commented Oct 10, 2018 at 14:10

GiulioP · Accepted Answer · 2018-10-10 12:48:56Z

4

How about using the Runtime.exec() method? Just do Process process = Runtime.getRuntime().exec("python script.py arg1 arg2"). Runtime is a class from the java.lang package, so you don't need to do any fancy import.

More info here.

EDIT

Ok, not too easy to manage if you have lots of functions. On the other hand if you don't mind a bunch of wrapper files just do a bit of code to build one automatically for each function.

Check out this little piece of Python code. Just replace foo with whatever your huge module is called, and you're good to go.

from inspect import getmembers, isfunction
import foo

f_list=[o[0] for o in getmembers(foo) if isfunction(o[1])]
for x in f_list:
    print("Build "+str(x))
    with open("helper_"+str(x)+".py","wt") as f:
        f.write("""import foo
import sys

arg_list=sys.argv[1::]
print(foo.{x}(*arg_list))""".format(x=x))

edited Oct 10, 2018 at 12:48

answered Oct 9, 2018 at 15:13

GiulioP

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3 Comments

Faram Over a year ago

This is exactly what I don't want to do. The problem here is, that I can't call a specific function. I've got a Python module with hundred of functions. I want to be able to call them individually. I know that I could do that with arguments (and switch case in the python script) or that I could put each function in a separate file, but that would be crazy. Considering that I need to debug here and then, it would be a problematic approach, too.

GiulioP Over a year ago

@TheOnionMaster Got it, please check out the edit to my answer. Is that un-crazy enough?

Faram Over a year ago

Perfect. Thanks!

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