Dash app re-performs early caching steps after loading server

When I spin up my Dash app, I do a bunch of once-off tasks - pulling in the data I'll need, etc. However, it seems like Dash is performing them twice: once at the point I'm asking for them to happen in the script, and a second time once it's loaded the server up.

Here's a simple example of what I'm talking about:

module_link_test_source.py

print("Source module")

def source_module_function():
    print("Source function")

    return 1

module_link_test_destination.py

import module_link_test_source as source
import dash
import dash_html_components as html

print("Destination module")
app = dash.Dash(__name__)

function_run = source.source_module_function()

app.layout = html.Div()

if __name__ =='__main__':
    app.run_server(debug=True)

When I run python module_link_test_destination.py, here's what the console spits out:

Source module
Destination module
Source function
Dash is running on http://127.0.0.1:8050/

 * Serving Flask app "module_link_test_destination" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: on
Source module
Destination module
Source function

I would only expect those print() statements to have executed once each. How do I make these steps only occur once?