Python percentage calculator I'm learning Python for 2 months now and I'm working on a little exercise app calculating percentages. I'd like to ask for a code review and comments. I'd like to make sure I'm following the right habits from the beginning.

# coding: utf-8

# In[9]:


def percA(perc, num):
    perc_a = perc/100 * num
    return perc_a

def percB(first, second):
    percB = first/second*100
    return percB

def percC(old, new):
    percC = (new - old)/old*100
    return percC

def percD(num, perc):
    perc = perc/100
    percD = num * (1 + perc)
    return percD

def percE(num, perc):
    perc = perc/100
    percD = num * (1 - perc)
    return percD

print("**************************************")
print("************** WELCOME ***************")
print("**************************************")
print("\n")
choose = input("Choose option:\nA. X% of Y\nB. X is what percent of Y\nC. By what percentage a number increased?\nD. Add percent to a number\nE.Substract percentage from a number\nYour answer: ")
if choose.isupper() == True:
    choose = choose.lower()
while choose == "a":
    if "a":
        usrperc = int(input("Provide percentage: "))
        usrnum = int(input("Provide number: "))
        result = percA(usrperc, usrnum)
        print("{0}% of {1} is {2}".format(usrperc, usrnum, result))
        break
    elif "b":
        usrperc = int(input("Provide percentage: "))
        usrnum = int(input("Provide number: "))
        result = percA(usrperc, usrnum)
        print("{0}% of {1} is {2}".format(usrperc, usrnum, result))
        break
else:
    print("Choose from range A - E")
You can call chose.lower without the if statement without any consequences as far as I know. I don’t have any experience with using something like while choose ==“a”, bit it looks to me like if choose ==“a” would work just the same way, and be more readable.