How to make the plot of number of students who are passed and fails

I have the data in .csv format and one column of them is the total score I want to count and plot the number of people who passes and fails right now I try using

def Grade(Total):
if Total >= 50:
    return("Pass")
else: return("Fail")

I try making something like Grade(['Total']) and didn't work and I realised that my function Grade() need to be number not string I want it to be the data frame shows how each rows(students) passes to fails what should I use instead of this? P.S. sorry I'm very new to stackoverflow and this post might have some flaws in it