This question already has answers here:
Evaluating a mathematical expression in a string
(14 answers)
Closed 4 years ago.
This is what I have so far:
import sys
first = float(sys.argv[1])
second = str(sys.argv[2])
third = float(sys.argv[3])
if second == "+":
print first + third
elif second == "-":
print first - third
elif second == "*":
print first * third
elif second == "/":
print first / third
elif second == "^":
print first ** third
else:
print "Invalid Operator"
The first and third arguments are supposed to be double floating point numbers. I wasn't sure how the operator is supposed to be represented, so I just named it "second" and set it as a string. I'm confused as to how I'm supposed to actually get the calculations. Are my if/elif/else statements wrong? Am I supposed to use "print" or "return" for actual calculations to be made?
This is an example of a test file:
def test_add(self):
output = self.runScript("simple_calc.py", "1", "+", "1")
result = float(output)
self.assertAlmostEqual(2.0, result, places=10)
output = self.runScript("simple_calc.py", "-1", "+", "1")
result = float(output)
self.assertAlmostEqual(0.0, result, places=10)
output = self.runScript("simple_calc.py", "1.0", "+", "-1.0")
result = float(output)
self.assertAlmostEqual(0.0, result, places=10)
your using = instead of ==
so it should be like this
if second =="+":
and do the same for all
= is an assignment statement not comparison
You could for example make a function called calculator and then use it with user inputs. :
def calculator(x, y, operator):
if operator == "+":
return x + y
if operator == "-":
return x - y
if operator == "*":
return x * y
if operator == "/":
return x / y
The x and y would of course be numbers user would input, operator is the operator of choice. So basically the function here would take 3 arguments.
Here is my solution:
def Operation():
while True:
operation = raw_input('Select operation: \n + = addition\n - = Subtraction\n * = multiplication\n / = Division\n')
if operation.strip() == '+':
break
elif operation.strip() == '-':
break
elif operation.strip() == '*':
break
elif operation.strip() == '/':
break
else:
print "Please select one of the operations"
continue
return operation
def number():
while True:
try:
number = int(raw_input("Please enter a number: "))
break
except ValueError:
print "Please enter valid number: "
return number
num1 = number()
operator = Operation()
num2 = number()
def calculate(num1, operator, num2):
if operator == "+":
return num1 + num2
elif operator == "-":
return num1 - num2
elif operator == "*":
return num1 * num2
elif operator == "/":
return num1 / num2
print calculate(num1, operator, num2)
Related
My Calculator is half working. I really put my brain in it but I cant figure out why its not working. Can someone help me?
number1 = input("Enter first number: ")
number2 = input("Enter second number: ")
operator = input("Enter the operation character: ")
result = number1 + operator + number2
if operator == '+':
result = int(number1) + int(number2)
elif operator == '-':
result = int(number1) - int(number2)
elif operator == '*':
result = int(number1) * int(number2)
elif operator == '/':
result = int(number1) / int(number2)
if number1.isdigit() == True:
print (result)
elif number2.isdigit() == True:
print(result)
else:
print("Enter a number.")
It's printing the calculated value, but if you enter a letter instead of a number.
For example:
Enter a first number: 5
Enter a second number: f
Now it should print "enter a number". But im getting this message istead
ValueError: invalid literal for int() with base 10: 'a'
if number1.isdigit() == True:
print (result)
elif number2.isdigit() == True:
print(result)
**else:
print("Enter a number.")**
You have lines like these:
if operator == '+':
result = int(number1) + int(number2)
Before lines like these:
if number1.isdigit() == True:
print (result)
elif number2.isdigit() == True:
print(result)
else:
print("Enter a number.")
So, if operater is indeed a +, Python will try to evaluate int(number1) + int(number2) and fail if number1 or number2 is not the string representation of a number.
This raises a ValueError (as it should) and a raised exception that isn't caught in a try .. except .. block will cause your program to terminated. You cannot continue with uncaught exceptions.
Either you should check first and then try to convert these strings, or you should catch the exception.
Also, you seem to expect your code to continue running after the mistake is made, so you'll need some sort of loop that keeps the program running until the user enters some input that makes sense.
I am not sure that I understood what you what but I think this solves the problem
number1 = input("Enter first number: ")
number2 = input("Enter second number: ")
operator = input("Enter the operation character: ")
result = number1 + operator + number2
if number1.isdigit() == True and number2.isdigit() == True:
if operator == '+':
result = int(number1) + int(number2)
elif operator == '-':
result = int(number1) - int(number2)
elif operator == '*':
result = int(number1) * int(number2)
elif operator == '/':
result = int(number1) / int(number2)
print (result)
else:
print("Enter a number.")
If you are just starting on coding, I suggest you to use this as a reason to search and learn on some few important concepts that will help you to get going.
First, you must validate your inputs before doing anything else with them. In your case, validate that your first and second numbers are actually valid integers, right after they are input. As it is the same validation to be done on both, you can create a function so you can reuse the logic.
def input_number():
num = input("Enter a number: ")
if num.isdigit():
return int(num)
else:
print("Invalid number.")
return input_number()
Here, I check if the input is valid (isdigit is true), and then I return the value already converted to int. If it is not, I call the same function again, and repeat the process. This is called recursion.
You should also validate the operator, because it is only valid among a few options.
def input_operator():
while True:
op = input("Enter the operation character: ")
if op in ["+", "-", "*", "/"]:
return op
else:
print("Invalid operator.")
Here I used a different technique. It is called while statement, and it will repeat the execution inside it until the condition is not True, or until it is explicitly broken (in this case, with a return statement).
Now, you have to add both function definitions on top of your code, then adjust you logic accordingly.
number1 = input_number()
operator = input_operator()
number2 = input_number()
if operator == "+":
result = number1 + number2
elif operator == "-":
result = number1 - number2
elif operator == "*":
result = number1 * number2
elif operator == "/":
result = number1 / number2
print (result)
I'm currently trying to make a small script which makes basic mathematical operations, and I want it to return to the number input depending if the user want or not to make another operation based on another input. I've already tried while loops and defining a function
Here is the code:
print('Hi!,this is a calculator')
#Here's where it should return
num1 = input('Please,enter a number ')
num2 = input('Enter another number ')
while True:
operator = input('Insert an operator +,-,*,/ ')
if operator != "+" and operator != "-" and operator != "*" and operator != "/":
print('Invalid Operator')
else:
if operator == "+":
result = int(num1) + int(num2)
result = str(result)
print('Your result is ' + result)
elif operator == "-":
result = int(num1) - int(num2)
result = str(result)
print('Your result is ' + result)
elif operator == "*":
result = int(num1) * int(num2)
result = str(result)
print('Your result is ' + result)
elif operator == "/":
result = int(num1) / int(num2)
result = str(result)
print('Your result is ' + result)
exit()
#Here's the repeating input
# repeat = input('Do you want to make another operation? Y/N ')
# repeat = repeat.lower()
# if repeat == 'y' or repeat == 'yes':
# else:
# exit()
You almost had it right. You can use a function to do the calculation, and call the function in a loop. If the user is finished, then break the loop.
EDIT: Added a loop to calculate() per the asker's specifications
print('Hi!, this is a calculator')
def calculate():
# loop in case the user entered an incorrect operator
while True:
num1 = input('Please,enter a number ')
num2 = input('Enter another number ')
operator = input('Insert an operator +,-,*,/ ')
if operator != "+" and operator != "-" and operator != "*" and operator != "/":
print('Invalid Operator')
continue # restart the calculation
else:
if operator == "+":
result = int(num1) + int(num2)
result = str(result)
print('Your result is ' + result)
elif operator == "-":
result = int(num1) - int(num2)
result = str(result)
print('Your result is ' + result)
elif operator == "*":
result = int(num1) * int(num2)
result = str(result)
print('Your result is ' + result)
elif operator == "/":
result = int(num1) / int(num2)
result = str(result)
print('Your result is ' + result)
return # Finished with this calculation
# continuously calculate until the user doesn't say yes
while True:
calculate()
repeat = input('Do you want to make another operation? Y/N ').lower()
if repeat != 'y' and repeat != 'yes':
break
Make two functions and put both functions in a loop.
def calculate(n1,n2):
oper = input("Enter operand: ")
#your if-elif block here
....
....
print("Your result is", ....)
def userInput():
num1 = input("Enter first num: ")
num2 = input("Enter second num: ")
return [num1,num2]
while True:
inlist = userInput()
calculate(inlist[0],inlist[1])
answer = input("Do you want another operation?")
if answer == "Y":
continue
else:
exit()
I got to do this calculator on python 3 that must execute on loop until the user types exit. Besides, programming ahead of the user typing invalid characters, such as letters when asked to type an operator or a number.
I must use while, if... However, I cannot use import.
while True:
operator = input("Give me an operator or \"exit\" to stop : ")
if operator == "exit":
break
if operator != "+" or "-" or "*" or "/":
print ("You must enter an operator")
break
no1 = input("Enter a number: ")
no2 = input("Enter a number: ")
if operator == "+":
output = int(num1) + int(num2)
elif operator == "-":
output = int(num1) - int(num2)
elif operator == "*":
output = int(num1) * int(num2)
else :
output = int(num1) / int(num2)
print("The result is " + str(result))
print("See you soon!")
I expect it to actually not stop when we enter anything but an operator, I want it to loop back to:
operator = input("Give me an operator or \"exit\" to stop : ")
You will find below this your code that work as expected, however lets start with general rules.
Be attentif, when you declare a variable, use the same elsewhere in your code.
Test, simple part of your code before trying to do a script. You condition to test operator was totally broken.
while True:
operator = input("Give me an operator or \"exit\" to stop : ")
if operator == "exit":
break
if operator not in [ "+", "-", "*" , "/"]: #<== here you condition is wrong ,do this instead
print ("You must enter an operator")
continue
try:
num1 = int(input("Enter a number: ")) #
num2 = int(input("Enter a number: ")) # <== both of this variable are not use else where ,rename to be consitdnt with the rest of your code
except ValueError:
print("Please enter an integer")
if operator == "+":
output = num1 + num2
elif operator == "-":
output = num1 - num2
elif operator == "*":
output = num1 * num2
else :
output = num1 / num2
print("The result is " + str(output)) #<=== here also, results was not defined
print("See you soon!")
Put a generic else statement which will continue with the next iteration.
if condition1 :
//logic
elif condition2 :
//logic
else:
continue
Your problem is that you are doing:
if operator != "+" or "-" or "*" or "/":
And what that is really doing, is that:
if operator != "+" or 45 or 42 or 47: (ASCII representation of these characters)
What this means, is that the condition is true no matter what, because or n where N is not 0, would pass any time.
You want:
if operator != "+" and operator != "-" and operator != "*" and operator != "/":
You want an AND gate.
Also, I noticed you are saying no1 = input(...) then doing int(num1) instead of int(no1).
As for jumping back to input, you use continue
Final code:
while True:
operator = input("Give me an operator or \"exit\" to stop : ")
if operator == "exit":
break
if operator not in [ "+", "-", "*" , "/"]: # credit to Florian Bernard for this line :)
print ("You must enter an operator")
continue
num1 = input("Enter a number: ")
num2 = input("Enter a number: ")
if operator == "+":
output = int(num1) + int(num2)
elif operator == "-":
output = int(num1) - int(num2)
elif operator == "*":
output = int(num1) * int(num2)
else:
output = int(num1) / int(num2)
print("The result is " + str(output)) # this was previously str(result) but result is was not defined
print("See you soon!")
BUT! if you are feeling new today, you can use the walrus operator introduced in PEP 572 and available from python 3.8
while (operator := input("Give me an operator or \"exit\" to stop : ")) != "exit":
if operator not in [ "+", "-", "*" , "/"]: # credit to Florian Bernard for this line :)
print ("You must enter an operator")
continue
num1 = input("Enter a number: ")
num2 = input("Enter a number: ")
if operator == "+":
output = int(num1) + int(num2)
elif operator == "-":
output = int(num1) - int(num2)
elif operator == "*":
output = int(num1) * int(num2)
else:
output = int(num1) / int(num2)
print("The result is " + str(output))
print("See you soon!")
EDIT:
Edited the final code to use continue, previous version was.
Also added a python 3.8 implementation.
EDIT2:
Just correcting some stuff, making sentences truer.
I am here trying to just make a simple calculator in python, and I wonder if its possible to make the 3 first lines in to one line when command run. What I mean with that is; I don't have to press enter to type the next number/operator but press space instead (in the input section).
while True:
import operator
num1 = int(input("Whats the first number:"))
oper = input("Which operator would you like to use: (+,-,/,*,**,^) :")
num2 = int(input("Whats the second number:"))
if oper == "+":
x = operator.add
elif oper == "-":
x = operator.sub
elif oper == "*":
x = operator.mul
elif oper == "/":
x = operator.__truediv__
elif oper == "**":
x = operator.pow
elif oper == "^":
x = operator.xor
else:
print("invalid input")
print(num1,oper,num2,"=",x(num1,num2))
You can use the split method of Python strings to accomplish this. Note that this code depends on three objects, separated by spaces, being entered. If more or fewer are entered or the spaces are forgotten, or either "number" is not actually an integer, there will be an error.
print("Enter a number, a space, an operator, a space, and another number.")
num1str, oper, num2str = input().split()
num1, num2 = int(num1str), int(num2str)
Rory's answer and comments pointed on the right direction, but here's a practical example:
operators = ["+","-","/","*","**","^"]
msg = f"Example query: 8 * 4\nAllowed operators: {', '.join(operators)}\nType your query and press enter:\n"
x = input(msg)
cmd_parts = [y.strip() for y in x.split()] # handles multiple spaces between commands
while len(cmd_parts) != 3: # check if lenght of cmd_parts is 3
x = input(msg)
cmd_parts = [y.strip() for y in x.split()]
# verification of command parts
while not cmd_parts[0].isdigit() or not cmd_parts[2].isdigit() or cmd_parts[1] not in operators :
x = input(msg)
cmd_parts = [y.strip() for y in x.split()]
num1 = cmd_parts[0]
oper = cmd_parts[1]
num2 = cmd_parts[2]
res = eval(f"{num1} {oper} {num2}")
print(num1,oper,num2,"=", res)
Python Example (Enable Interactive mode)
calc=input("type here:- ").split()
# type belove with space between
num1,operatoe,num2=calc[:]
# if length of calc doesn't equal to three you can continue with while loop
print(num1,operator,num2)
An improved working calculator which handles some errors based on other answers:
import operator
x = {
"+": operator.add,
"-": operator.sub,
"*": operator.mul,
"/": operator.__truediv__,
"**": operator.pow,
"^": operator.xor
}
while True:
print("Enter a number, a space, an operator, a space, and another number.")
try:
num1str, oper, num2str = input().split()
num1, num2 = int(num1str), int(num2str)
print(num1,oper,num2,"=",x[oper](num1,num2))
except:
print("invalid input")
This question already has answers here:
How can I read inputs as numbers?
(10 answers)
Closed 7 years ago.
So, once I ran the code, the question() returns 'Incorrect', even I'm pretty sure that I put in the right answer.
P.S. The operator() function is alright I checked it; it's only the question() that needs attention.
import random
def numberRan(): # Generate a random number
return random.randint(1, 10) # No arguments needed for this
def operator():
operator = ""
number = random.randint(1, 3)
if number == 1:
operator = "+"
elif number == 2:
operator = "-"
else:
operator = "x"
return operator
def question():
num1 = numberRan()
num2 = numberRan()
realAnswer = 0
int(realAnswer)
oper = operator()
answer = input(str(num1) + str(oper) + str(num2) + "= ")
if oper == "+":
realAnswer = num1 + num2
elif oper == "-":
realAnswer = num1 - num2
elif oper == "x":
realAnswer = num1 * num2
if realAnswer == answer:
return "Correct"
else:
return "Incorrect"
question()
You never convert your answer to an int, so your answer (the result of input(...) is still a str. You're then comparing that str to realAnswer, which is an int: comparing an int and str will be always False.
Just change one line:
answer = input(str(num1) + str(oper) + str(num2) + "= ")
to
try:
answer = int(input(str(num1) + str(oper) + str(num2) + "= "))
except ValueError:
import sys
sys.stderr.write("your input was not an integer number")
return "Incorrect"
if oper == "+":
...
Note the try-except clause: now, there's an explanatory error message if the input was not a number.