Back to coding...

ilan · Jul 17, 2026

After a short break, I’m back to coding.
I’ve been playing around with PyBridge, and I have to say, this might be the most impressive library Erel has created in years. I already finished my B4J server using a great Python library I downloaded, and everything works beautifully.

Now I’m working on the B4X clients, and I’ll upload them to the store soon. The huge advantage here is how easily we can use external Python libraries. I even configured the server to use the
latest Python framework instead of the minimal version bundled with B4J, and it runs perfectly.

B4X:

Dim opt As PyOptions = Py.CreateOptions("C:\Users\ilan1\AppData\Local\Programs\Python\Python314\python.exe")

This is a game changer. We can build so many powerful things while still staying in our familiar environment.

THANK YOU @Erel

hatzisn · Jul 17, 2026

I have tried it too. It is incredible. And the fact that it is implementable in B4J it is a plus^2. The only caveat is if the python code has long processing time you cannot implement it easily in a WebApp because the calls are sequential. Although I cannot understand why is this happening... Since it is communication with open ports why don't we run more instances of the bridge in the Java part (or one instance with multiple open ports in different threads) and the Python part will just communicate in different ports with the Java side bridge as different instances (I am not familiar with threads in the Python side). It is just a Try-Except block to select the appropriate port in python side or am I thinking it is easy because I have not checked the implementation?

Erel · Jul 19, 2026

I agree that PyBridge is a great library and open many options that were previously difficult to achieve.

@hatzisn the solution for such cases is usually to implement it with async methods that do not block the python process. PyBridge support such methods with Py.RunCodeAwait and Wrapper.RunAwait.

ilan · Jul 19, 2026

Erel said:
@hatzisn the solution for such cases is usually to implement it with async methods that do not block the python process. PyBridge support such methods with Py.RunCodeAwait and Wrapper.RunAwait.

i did it like this:

B4X:

Wait For (pyw.Fetch) Complete (Result As PyWrapper)

and also added at the end of the function:

B4X:

StopMessageLoop

after its done i call again:

B4X:

StartMessageLoop

the important thing is NOT TO RUN A ASYNC METHOD INSIDE THE HANDLER!!

i tried running 50 calls to the server at the same time and all went through and all responded back.

B4X:

for /l %i in (1,1,50) do curl "http://localhost/ai/apitest1?text=בערב קיץ חמים ישב דניאל על ספסל העץ שבקצה החצר והרוח נשאה ריח של יסמין והירח עלה לאט מעל הגגות"

if there is a better solution, could you please upload a simple version how to make async calls to PyBridge?

Magma · Jul 19, 2026

ilan said:
i did it like this:

B4X:

Wait For (pyw.Fetch) Complete (Result As PyWrapper)

and also added at the end of the function:

B4X:

StopMessageLoop

after its done i call again:

B4X:

StartMessageLoop

the important thing is NOT TO RUN A ASYNC METHOD INSIDE THE HANDLER!!

i tried running 50 calls to the server at the same time and all went through and all responded back.

B4X:

for /l %i in (1,1,50) do curl "http://localhost/ai/apitest1?text=בערב קיץ חמים ישב דניאל על ספסל העץ שבקצה החצר והרוח נשאה ריח של יסמין והירח עלה לאט מעל הגגות"

if there is a better solution, could you please upload a simple version how to make async calls to PyBridge?

welcome back @ilan ...b4x is better with company!

websockets with call backs work better for python... but always is how your want your app to works..

b4j combines many technolgies under one package...

hatzisn · Jul 19, 2026

Erel said:
I agree that PyBridge is a great library and open many options that were previously difficult to achieve.

@hatzisn the solution for such cases is usually to implement it with async methods that do not block the python process. PyBridge support such methods with Py.RunCodeAwait and Wrapper.RunAwait.

Would it be possible to post an example?

If I run it with Await then is this code correct?

B4X:

Wait For (py.RunCodeAwait("DoSomething", Array(sString1, sString2, sString3), sCode)) Complete (lRet As PyWrapper)

While with run code I do this to get the list returned from Python (with Fetch):

B4X:

Wait For (py.RunCode("DoSomething", Array(sString1, sString2, sString3), sCode).Fetch) Complete (lRet As PyWrapper)

The DoSomething sub in Python calls an OnLine http service that answers after some time.

ilan · Jul 19, 2026

Magma said:
websockets with call backs work better for python... but always is how your want your app to works..

i though about using websocket but because its not a feature that make sense to use in my scenario because all i do is a get request to the api and return a value i dont need to stay connected so using handler is more the right way in my case.

ilan · Jul 19, 2026

hatzisn said:
Would it be possible to post an example?

If I run it with Await then is this code correct?

B4X:

Wait For (py.RunCodeAwait("DoSomething", Array(sString1, sString2, sString3), sCode)) Complete (lRet As PyWrapper)

While with run code I do this to get the list returned from Python (with Fetch):

B4X:

Wait For (py.RunCode("DoSomething", Array(sString1, sString2, sString3), sCode).Fetch) Complete (lRet As PyWrapper)

The DoSomething sub in Python calls an OnLine http service that answers after some time.

it should look like this:

B4X:

Sub Handle(req As ServletRequest, resp As ServletResponse)
    resp.ContentType = "application/json; charset=utf-8"
   
    Dim action As String = req.RequestURI.ToLowerCase
    If action.EndsWith("/test") Then
        Dim txt As String = req.GetParameter("text")
        If txt.Length = 0 Then
            resp.Write("{""error"":""missing text""}")
            Return
        End If
        runTest(txt,resp)
        StartMessageLoop
    Else
        resp.Write("{""error"":""unknown endpoint""}")
    End If
End Sub

Sub runTest(txt As String,resp As ServletResponse)
    Dim pyw As PyWrapper = test1(txt)
    Wait For (pyw.Fetch) Complete (Result As PyWrapper)
    Dim jg As JSONGenerator
    jg.Initialize(CreateMap("text":txt))
    resp.ContentType = "application/json; charset=utf-8"
    resp.Write(jg.ToPrettyString(2))
    StopMessageLoop
End Sub
 
Sub test1(txt As String) As PyWrapper
    Dim code As String = $"
def test1(text):
    return text
"$
    Return Main.Py.RunCode("test1",Array(txt),code)
End Sub

i am including a example project and you can try. i have also tested in CMD and all requests went trough

Erel · Jul 19, 2026

Two important links about servers and PyBridge:

[PyBridge][server] Using PyBridge in web apps

PyBridge must be accessed from a single thread. In server solutions, each handler runs in its own thread so we need to add some barriers to ensure proper usage. The way to implement it is by adding a background worker dedicated to PyBridge. Other handlers make requests to this worker using...

www.b4x.com

[PyBridge] [Server] Online charts with Plotly

Porting of this desktop example: https://www.b4x.com/android/forum/threads/pybridge-visualization-of-hierarchical-data-with-plotly.167965/ to jServer. PyBridge runs with a background worker and the interaction with this worker is done with CallSubDelayed. This ensures that the code will be...

www.b4x.com

ilan · Jul 19, 2026

thank you erel for the examples. they are very useful. i dont need websocket in my web api. all calls are done to handlers. is my solution (example in post #8) correct? can i use it like this? (it works but i am not sure its the correct way to do it)

hatzisn · Jul 19, 2026

Erel said:
Two important links about servers and PyBridge:

[PyBridge][server] Using PyBridge in web apps

PyBridge must be accessed from a single thread. In server solutions, each handler runs in its own thread so we need to add some barriers to ensure proper usage. The way to implement it is by adding a background worker dedicated to PyBridge. Other handlers make requests to this worker using...

www.b4x.com

[PyBridge] [Server] Online charts with Plotly

Porting of this desktop example: https://www.b4x.com/android/forum/threads/pybridge-visualization-of-hierarchical-data-with-plotly.167965/ to jServer. PyBridge runs with a background worker and the interaction with this worker is done with CallSubDelayed. This ensures that the code will be...

www.b4x.com

The first I have tried it in the past but the second I have not. Quite Impressive.
I tried to find "Await" in both examples but I could not find it. Can you please post also an example with RunCodeAwait.

Maybe when I return home I will try it with my code to check it.

ilan · Jul 19, 2026

hatzisn said:
The first I have tried it in the past but the second I have not. Quite Impressive.
I tried to find "Await" in both examples but I could not find it. Can you please post also an example with RunCodeAwait.

Maybe when I return home I will try it with my code to check it.

check also post #8 this may solve your issue

hatzisn · Jul 19, 2026

ilan said:
check also post #8 this may solve your issue

You also execute py.RunCode...

ilan · Jul 19, 2026

hatzisn said:
You also execute py.RunCode...

Erel · Jul 20, 2026

Your solution is not 100% correct. It will fail if multiple calls are made concurrently. Remember that with jServer requests are handled concurrently (in release mode).

The safe solution is to use a background worker that owns and manages PyBridge. Other handles call it with CallSubDelayed and wait for its response.

For simple cases, you can configure the handler to be a single thread handler: srvr.AddHandler("/test/*", "testHandler", True), but this is not scalable.

ilan · Jul 20, 2026

Erel said:
Your solution is not 100% correct. It will fail if multiple calls are made concurrently. Remember that with jServer requests are handled concurrently (in release mode).

The safe solution is to use a background worker that owns and manages PyBridge. Other handles call it with CallSubDelayed and wait for its response.

For simple cases, you can configure the handler to be a single thread handler: srvr.AddHandler("/test/*", "testHandler", True), but this is not scalable.

This is the problem i am facing now. Everything works in debug mode but in release it doesnot work. Stopmessageloop ends the server and without it it even doesnot work in debug mode.

What would be the right way to do using handlers and not websocket?

Magma · Jul 20, 2026

ilan said:
This is the problem i am facing now. Everything works in debug mode but in release it doesnot work. Stopmessageloop ends the server and without it it even doesnot work in debug mode.

What would be the right way to do using handlers and not websocket?

why not combine them ?

Erel · Jul 20, 2026

ilan said:
What would be the right way to do using handlers and not websocket?

I will create a small example

josejad · Jul 20, 2026

hatzisn said:
The only caveat is if the python code has long processing time you cannot implement it easily in a WebApp because the calls are sequential.

Erel said:
The safe solution is to use a background worker that owns and manages PyBridge. Other handles call it with CallSubDelayed and wait for its response.

I think this thread is becoming something that deserves a place in the B4J [PyBridge] forum

Erel · Jul 20, 2026

josejad said:
I think this thread is becoming something that deserves a place in the B4J [PyBridge] forum

I've created a related "code snippet": [PyBridge][Server] PyBridge with standard handlers - Erel

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