Location is None when initializing with pn.serve (but works when served from commandline)

Panel
,
1

I have a successfully working Panel multi-page application that can be run via commandline using panel serve page1.py page2.py page3.py

I thought I would refactor this into a single app.py to programmatically launch my multipage Panel application. The application looks something like this:

import views
...

pn.extension("tabular")

page1 = views.Page1()
page2 = views.Page2()
page3 = views.Page3()

pn.serve({
    "page1":page1.get_page,
    "page2":page2.get_page,
    "page3":page3.get_page,
})

where each Page is a Python class with a defined function get_page that returns a template object.

Since I want to provide some session state for individual users via url, I sync the pn.state.location url with one of the current widgets/variables:

# in views.py
class Page1:
    def __init__(self,*args,**kwargs):
        ...
        self.variable = pn.widgets.Select(...)
        pn.state.location.sync(self.variable, {"value":"variable"})
    ...

This works fine when using panel serve however, when refactoring into the singular app.py listed above and running python -m app.py via commandline, I am met with the following error:

Traceback (most recent call last):
  File "~/app.py", line 13, in <module>
    page1 = views.Page1()
                   ^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/sundeep/moi/work/safeyou/app/views.py", line 52, in __init__
    pn.state.location.sync(self.variable, {"value":"variable"})
    ^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'sync'

Which suggests that pn.state.location is not initialized. Does anyone have any suggestions how to go about amending this or what the issue might be?

2

Try adding an if pn.state.location

3

Thanks @ahuang11 , this works however leaves the option of syncing unavailable the first time the page is loaded. Do you know any way pn.state.location could be initialized beforehand?

4

I think you might want to file an issue