Multiple numbers calculator

Question

This is my first ever Python program so I would really like to know if it's any good (I mean if it is well writen), and if not then how to make it better. I would also like to know if there is a way to get all the veriables in one line without a space between them.

This calculator is basicly this calculator which I wrote in C++ upgraded and writen in Python.

def calculate(num1, num2, act):
 if(act=='+'):
 total=num1+num2
 elif(act=='-'):
 total=num1-num2
 elif(act=='*'):
 total=num1*num2
 elif(act=='/'):
 total=num1/num2
 else:
 print("input not recognized")
 return total
def calc2():
 user_input=input("Enter a num1 act num2 (with a space between them): ") #Gets the values
 var1, action, var2=user_input.split() #assigns the values into the variables
 if(action=='/' and var2==0): #checks for division by 0
 print("YOU CAN'T DIVIDE BY ZERO!!!")
 else:
 print(calculate(float(var1), float(var2), action)) #calls the 'calculating' function, recives and prints the total of act
def calc3():
 user_input=input("Enter a num1 act1 num2 act2 num3 (with a space between them): ") #Gets the values
 var1, action1, var2, action2, var3=user_input.split() #assigns the values into the variables
 if(action1=='/' and var2==0 or action2=='/' and var3==0): #checks for division by 0
 print("YOU CAN'T DIVIDE BY ZERO!!!")
 elif((action2=='*' or action2=='/') and (action1=='+' or action2=='-')): #checks if act2 should be done before act1 (order of operation)
 total=calculate(float(var2), float(var3), action2) #calls the 'calculating' function, recives the total of act2
 print(calculate(float(var1), float(total), action1)) #calls the 'calculating' function, assigns the total of act2 as num2, recives and prints the total of act1
 else: #act1 is done before act2 (order of operation)
 total=calculate(float(var1), float(var2), action1) #calls the 'calculating' function, recives the total of act1
 print(calculate(float(total), float(var3), action2)) #calls the 'calculating' function, assigns the total of act1 as num1, recives and prints the total of act2
def main():
 amount=float(input("How many numbers? (2-3 numbers) "))
 if(amount==2):
 calc2()
 elif(amount==3):
 calc3()
 else:
 print("I SAID TWO OR THREE NUMBERS")
main() #starts program

---

Input/Output

Input:2 + 3 * 4
Output:14

Answer 1

There are some places where you can dictionaries instead of if/elif/else statements, I will analyze one here:

if(act=='+'):
 total=num1+num2
elif(act=='-'):
 total=num1-num2
elif(act=='*'):
 total=num1*num2
elif(act=='/'):
 total=num1/num2
else:
 print("input not recognized")

Is often re-written as a dictionary. So, you could create a dictionary called OPS and write:

import operator
OPS = {
 '+' : operator.add,
 '-' : operator.sub,
 ...
}
ERROR = lambda arg1, arg2: print("input not recognized")

You can then you can do:

def calculate(num1, num2, act):
 return OPS.get(act, ERROR)(num1, num2)

This tries getting the particular key which is a function. It then calls it. If the operator is not found, it defaults to the ERROR.

• Graipher: I would use a try..except KeyError instead of dict.get, but otherwise nice answer.