How to make if statement with combobox

If statement With Combobox

I am Making App for Calculating BMI with GUI And I make Combobox For Select Gender like (Male, Female, Child) And You Know that the BMI result (obese or underweight.... ) will Be different Between Male, Female, And Child so I want when the user selects Gender ... if the selected Gender is male will print normal (18-25) And When the user select Gender is the child normal is (14-18) etc... Please help me to do that... My code wrote with python Thanks!