# Плохо
return render_template("index.html", form = data, goals = goals, id_list = id_list)

variableName = ...

date_time = week_days[request.form["clientWeekday"]] + ", " + request.form["clientTime"]


# Хорошо
return render_template("index.html", form=data, goals=goals, id_list=id_list)

variable_name = ...


week_days = week_days[request.form["clientWeekday"]] 
some_var =  request.form["clientTime"]
date_time = f"{week_days} {some_var}"