Python Meeting Düsseldorf - Spring Sprint 2024

• Python Meeting Düsseldorf: https://www.pyddf.de/
• Sprint Meetup page: https://www.meetup.com/python-meeting-dusseldorf/events/299529260/

Experiments with Taipy

Resources

• Github project: https://github.com/malemburg/pyddf-spring-sprint-2024
• Taipy home page: https://www.taipy.io/
• Documentation: https://docs.taipy.io/en/latest/
• Get started: https://docs.taipy.io/en/latest/getting_started/
• Intro video: https://www.youtube.com/watch?v=PDkP1jxXfiA
• Weather data for Düsseldorf: https://meteostat.net/de/station/10400?t=2024-02-25/2024-03-03

Prepare env

• make install-venv install-requirements
• create exampleN.py files based on Getting Started guide and tutorial

Observations

example1.py

• global vars are just used for initialization, not updated later on
  • updates go into state parameter of on-change APIs
• adding new variables requires a restart
  • the auto reloader doesn't seem the handle them correctly and creates weird errors
• auto reload also doesn't update when markdown is changed
  • it seems the auto-reloader isn't ready for prime time yet
• markdown for headers does not seem to apply to widgets
  • widget sizes don't adapt automatically
• Taipy appears to use some WASM as runtime
  • ca. 10MB in total
• Uses WebSockets for interactivity
  • slider changes are reported via WS
• Restarting the app causes a new browser tab to open
  • if you don't pay attention, you suddenly have 10s of tabs all listening and working with the same backend app, making it very sluggish
• Changes to state variables propogate to the client side automatically
  • You can also call other functions from an on_change trigger function. If those functions change state, these changes will also propagate.
• Taipy uses Plotly for charting
  • full Plotly charting API available for customization
• All global variables get converted into state variables and are subject to the automatic state exchange with the client

example2-5.py

• The Taipy UI does not indicate when the server connection goes down
  • perhaps there's some way to create a widget for this
• There doesn't appear to be a way to select rows of a table and interact with them
  • It is possible to set a callback when selecting rows and marking selected rows would be possible via a CSS callback, but that's cumbersome
  • Should be a standard parameter of tables
• When defining widget properties, just listing the property name will implicitly add an =True, e.g. |filter| is the same as |filter=True|

sheetviewer.py

• Editing dataframes should be done by copying the state.dataframe and then assigning back the edited version
  • Otherwise Taipy doesn't notice the data change
• on_action on tables gets called when a row is selected
  • this gets data in form of a dict {'action': 'on_select', 'index': 0, 'col': 'colname', 'args': []}
  • unfortunately, the column name is passed back, not the integer value, which makes it difficult to figure out exactly which column was clicked if column names are not unique
• Table height property doesn't work with % notation
  • px notation appears to work
• File upload widget saves to /tmp
  • doesn't clean up after itself
  • appends numbers to the filename to make them unique
• Styling
  • see https://docs.taipy.io/en/latest/manuals/gui/styling/#style-sheets
  • passing in css_file to the Gui constructor doesn't appear to work
    • could be a mistake on my side: adding this keyword to the .run() method doesn't create an error and I may have placed it there
  • what does work is naming a CSS file after the file defining the app
• The selected property on tables dosen't do anything much
  • better build your own selection mechanism
• The table auto_loading property doesn't work reliably and messes up the CSS it seems
• Table property page_size_options doesn't appear to work. page_size on its own does work.
• Selector property width doesn't work
  • as a work-around, define a wide-selector CSS class and set this using class_name=wide-selector on the widget