python类中的简单计算器

Question

I'm lagging in logic that the following basic script should not ask to enter the input of A and B even after giving the irrelevant numbers that's greater than 5.

#!/usr/bin/python
try :
     print "Enter 1 for Addition "
     print "Enter 2 for Subtraction"
     print "Enter 3 for Multiplication"
     print "Enter 4 for Divition"

     class calc :

        def Add ( self, A, B ):
           print A + B
        def Sub (self, A, B ):
           print A - B
        def Mul (self, A, B ):
           print A * B
        def Div (self, A, B ):
           print A / B

    C = calc()

    Input = int (raw_input ("Enter the choice:"))

    A = int (raw_input ("Enter A:"))
    B = int (raw_input ("Enter B:"))

    if Input == 1:
          C.Add (A,B)
    elif Input == 2:
          C.Sub (A,B)
    elif Input == 3:
          C.Mul (A,B)
    elif Input == 4:
          C.Div (A,B)
    elif Input <= 5:
          print "Its not avaliable try again"
          exit ()

except ValueError:
      "The value is wrong"

Answer 1

Your entire if ... elif chain is better handled using a dict structure like this:

try:
    {1: C.Add, 2: C.Sub, 3: C.Mul, 4: C.Div}.get(Input)(A,B)
except TypeError: 
    print "It's not available, try again"
    exit()

Answer 2

You can move the condition which checks for wrong user input to the line next to the raw_input invocation (and fix the issue in the statement itself - the wrong choices are choices which are bigger than 4 and less than 0):

C = calc()

Input = int (raw_input ("Enter the choice:"))

if Input not in [1,2,3,4]:
    print "Its not avaliable try again"
    exit ()

BTW: it'll be better to wrap in try/except block only the lines which can cause the exception, not the whole program:

C = calc()
try:
    Input = int (raw_input ("Enter the choice:"))
except ValueError:
    print "Wrong input"
    exit()

if Input not in [1,2,3,4]:
    print "Its not avaliable try again"
    exit ()

Also, it'll be better to use naming conventions: names of variables should start with non-capitalized letter, eg input , names of classes should start with capitalized letters - class Calc .

Answer 3

Instead of

... 
elif Input <= 5: # This doesn't make sense, this check will work just for negative numbers
    print "Its not avaliable try again"
    exit ()

use

...
else:
    print "Its not avaliable try again"
    exit ()