how to block python code execution till js snippet returns in Jupyter notebook about ipython_blocking

[kafonek]

Hi @theSuiGenerisAakash, I'm afraid I don't have a good answer for you. What's happening is that func() is getting executed and returns a Javascript object that evaluates as True if you bool() it. That gets you out of the %block command immediately.

When the Python kernel receives the code and executes it, it's actually sending another message asynchronously back to the front end to execute the javascript (setting notebook_name). When the front-end receives that, it sends a execute_request message to the Python kernel (again asynchronously) to eval that Python code (notebook_name = 'Untitled.ipynb' or whatever your name is).

I believe if you keep fiddling, you'll get to something like this:

### cell 1
import ipython_blocking
import IPython
from IPython.core.magics.display import Javascript
Javascript("IPython.notebook.kernel.execute(`notebook_name = '${IPython.notebook.notebook_name}'`)")

### cell 2
def block():
    try:
        return notebook_name
    except NameError:
        pass

### cell 3
%block block

### cell 4
print(notebook_name)

If you run those cells manually with a second or so pause in between, then it will work and notebook_name is set. However if you cell -> run all it will block forever. Ultimately ipython_blocking is only good for blocking and capturing/replaying execute_request messages while watching comm_msg (widget changes) in order to break out of the context. In the example above, the execute_request notebook_name = ... message that's eventually getting triggered asynchronously by the first cell gets queued up behind cell 3 and is captured instead of executed, so you'll never break out of the context.

I'm afraid you'll have to look around for other options to get your notebook name within the Notebook. Thanks.

[theSuiGenerisAakash]

This is as I had thought, thanks for the detailed explanation. Please let me know if I should close the issue.