dash_functions.py

# ========== Callbacks ================
@app.callback(Output('line-chart-1', 'figure'),
              [Input('dropdown-1', 'value')])
def update_graph(selected_dropdown_value):
    dff = filter_df(selected_dropdown_value)
    return {
        'data': [{
            'x': dff.Date,
            'y': dff.QuoteCount,
            'line': {
                'width': 3,
            }
        }],
    }
}

# ========== Functions ================
def filter_df(df, names):
    dff = df[df['Date'] == selected_dropdown_value]
    # Perform more complex actions here
    # .
    # .
    return dff