A Function is the simple callable object in python. A function can accept some arguments and possibly return some object. The following python code represents the basic calculator operation like addition, subtraction, multiplication and division. The code is well organized with different functions. Sample Flowchart can access from here

```# menu() function prints the main menu, and prompts for a choice
#print what options you have
print "Welcome to calculator in Python"
print " "
print "2) Subtraction"
print "3) Multiplication"
print "4) Division"
print "5) Quit calculator"
print " "
return input ("Choose your option: ")

# this adds two numbers given
print a, "+", b, "=", a + b

# this subtracts two numbers given
def sub(a,b):
print b, "-", a, "=", b - a

# this multiplies two numbers given
def mul(a,b):
print a, "*", b, "=", a * b

# this divides two numbers given
def div(a,b):
print a, "/", b, "=", a / b

# NOW THE PROGRAM STARTS, AS CODE IS RUN
loop = 1
choice = 0
while loop == 1:
if choice == 1:
elif choice == 2:
sub(input("Subtract this: "),input("from this: "))
elif choice == 3:
mul(input("Multiply this: "),input("by this: "))
elif choice == 4:
div(input("Divide this: "),input("by this: "))
elif choice == 5:
loop = 0

print "Thankyou for using calculator!"

# End of the program```

OUTPUT:

```Welcome to calculator in Python

2) Subtraction
3) Multiplication
4) Division
5) Quit calculator

to this: 35
25 + 35 = 60
Welcome to calculator

2) Subtraction
3) Multiplication
4) Division
5) Quit calculator

Multiply this: 15
by this: 10
15 * 10 = 150
Welcome to calculator