Assigning user input operators to variables

Question

I'm trying to set up a situation in which the user inputs a number and an operator and the output is the (user number) (user operator) on a list of 1 through 10.

This is hard to explain, but here's the code:

num = int(input("Enter a number greater than 1: "))

oper = input("Choose a math operation (+, -, *): ")
for i in range(1, 11):
    print(num)

And I get lost there. I want to get something that looks like

num   oper   1   =   (whatever num and the operator and 1 equal)
num   oper   2   =   (whatever num and the operator and 2 equal)

And so on.

So my question is: How do you assign a user-inputted operator to a variable?

JCVanHamme · Accepted Answer · 2016-01-26 03:06:28Z

4

Another possibility is to use the operator module to set up a dictionary of operator functions, like so:

import operator

operator_dict = {
    '+': operator.add,
    '-': operator.sub,
    '*': operator.mul,
}
num = int(input("Enter a number greater than 1: "))

oper = input("Choose a math operation (+, -, *): ")
for i in range(1, 11):
    print(operator_dict[oper](float(num), i))

An example session:

Enter a number greater than 1: 3
Choose a math operation (+, -, *): *
3.0
6.0
9.0
12.0
15.0
18.0
21.0
24.0
27.0
30.0

answered Jan 26, 2016 at 3:06

JCVanHamme

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Comments

intboolstring · Accepted Answer · 2016-01-26 02:58:12Z

3

From what you say here:

I'm trying to set up a situation in which the user inputs a number and an operator and the output is the (user number) (user operator) on a list of 1 through 10.

I think you want to do this:

num = int(input("Enter a number greater than 1: "))

oper = input("Choose a math operation (+, -, *): ")
for i in range(1, 11):
    if oper == "+":
       print(num+i)
    elif oper == "-":
       print (num-i)
    elif oper == "*":
       print (num*i)

answered Jan 26, 2016 at 2:58

intboolstring

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4 Comments

tonyl7126 Over a year ago

this is good but you could move the if block outside the loop

abe Over a year ago

This is something that eval can be used for in a more efficient way.

intboolstring Over a year ago

Eval is something you generally want to avoid, even though it can help.

tonyl7126 Over a year ago

I prefer the if block (or a dictionary lookup) as it allows the programmer to control exactly which operations are allowed

midori · Accepted Answer · 2016-01-26 02:59:44Z

3

Seems like you want something like this:

num = int(input("Enter a number greater than 1: "))

oper = raw_input("Choose a math operation (+, -, *): ")
for i in range(1, 11):
    if oper == '+':
        print(num, oper, i, '=', num + i)
    elif oper == '-':
        print(num, oper, i, '=', num - i)
    elif oper == '*':
        print(num, oper, i, '=', num * i)
    else:
        print('operator is not supported')

Output:

Enter a number greater than 1: 2
Choose a math operation (+, -, *): *
2 * 1 = 2
2 * 2 = 4
2 * 3 = 6
2 * 4 = 8
2 * 5 = 10
2 * 6 = 12
2 * 7 = 14
2 * 8 = 16
2 * 9 = 18
2 * 10 = 20

answered Jan 26, 2016 at 2:59

midori

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Comments

abe · Accepted Answer · 2016-01-26 03:10:59Z

2

Eval can be used here:

num = str(input("Enter a number greater than 1: "))

oper = str(input("Choose a math operation (+, -, *, /, %, //): "))
if oper in ["+", "-", "*", "/", "%", "//"]:
    for i in range(1, 11):
        operation = num + oper + str(i) #Combine the string that is the operation
        print("{} {} {} = {}".format(num,oper,str(i),eval(operation)))
else: #if it is not in our approved items
    print("Operation not supported.")

edited Jan 26, 2016 at 3:10

answered Jan 26, 2016 at 2:59

abe

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Comments

Pax Vobiscum · Accepted Answer · 2016-01-26 03:02:15Z

1

I think the easiest way to do this to create a function, which within itself has all these if/elif conditions, since python does not recognize strings as operators.

The function may look a little bit like:

def operation(number1, number2, operator):
    if operator == '+':
        return number1 + number2
    elif operator == '-':
        return number1 - number2

And so on. Then you can call this function in a for loop, like this:

for n in range(10):
    otherNumber = n + 1
    print(yourNumber, otherNumber, operator)

answered Jan 26, 2016 at 3:02

Pax Vobiscum

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