Merely changes from Fahrenheit to Celcius then the weather data would have to be re-downloaded, whichĬan be time consuming. You could have one callback that outputs the temperatureīy taking both the date and the temperature unit as inputs, but this means that if the user Then displays the temperature for that day. Your Dash app allows a user to select a date and a temperature unit (Fahrenheit or Celcius), and For example, if some data needs to be queried from a database and then displayed inīoth a graph and a table, then you can have one callback that calculates the data and createsīut sometimes having multiple outputs in one callback isn’t a good solution. One way to achieve this is by having multiple outputsįor one callback: the expensive task can be done once and immediately used in all the You can have one callback run the task and then share the results to the other callbacks. Rather than have each callback run the same expensive task, Processing tasks like making database queries, running simulations, or downloading data. In some apps, you may have multiple callbacks that depend on expensive data This chapter explains why and provides some alternative patterns for It is not safe to modify any global variables. (/basic-callbacks) is that Dash Callbacks must never modify variables outside of their One of the core Dash principles explained in the Just getting started? Make sure to install the necessary The rest of the Dashĭocumentation covers other topics like multi-page apps and component The previous chapter covered how to use callbacks This is the final chapter of the essential Dash Fundamentals.
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