Assigning operator to a variable in Python [duplicate]

Question

I'm a beginner in Python and I can't figure out the assignment of an operator to a variable.

I've read assign operator to variable in python? but I still can't figure out my problem.

a = str(+) This line of code gives an Invalid Syntax Error.

Whereas, a =input() works completely fine when we give an operator as input. This operator is stored as string type because whatever you enter as input, input function converts it into a string.

Why str() is not able to store an operator as a string whereas input() can do the same task without any error?

But the user isn't giving an operator as input. The user is giving a string, "+", which merely happens to resemble the addition operator. It's a use-mention distinction sort of thing. — Kevin
– Kevin, Commented Sep 17, 2019 at 13:29
For your situation, you should be able to just do this: a = "+" — Jop Knoppers
– Jop Knoppers, Commented Sep 17, 2019 at 13:32

OneCricketeer · Accepted Answer · 2019-09-17 13:33:05Z

2

Based on the other post, you'd have to do

import operator
a = operator.add

The answer there just does a lookup in a dictionary

You're not giving an operator to input(), you're always inputting and outputting a string, which could be any collection of characters & symbols

edited Sep 17, 2019 at 13:33

answered Sep 17, 2019 at 13:29

OneCricketeer

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4 Comments

chepner Over a year ago

I'm almost certain the OP does not want a = '<built-in function add>', a string representation of a built-in function.

chepner Over a year ago

a = operator.add, though, may be a possibility.

PyM Over a year ago

Actually I'm trying to write a function to design a calculator which takes two values and an operator in the form of variable as an argument. The operation is performed on the values on the basis of the operator received, but I was not able to store the operator in a variable.

OneCricketeer Over a year ago

You can just store the characters, then compare and do the appropriate ops. There's several ways to handle it martinbroadhurst.com/shunting-yard-algorithm-in-python.html

chepner · Accepted Answer · 2019-09-17 13:32:18Z

2

+ is not an identifier or value of any kind; it is part of Python's syntax. You probably want a = str("+") (or simply a = "+").

input doesn't take a value; whatever environment you are running in already takes care of converting your keystrokes to strings for input to read and return.

If you want a to be a callable function, then you can use operator.add as mentioned in @cricket_007's answer (though not passed through str, but used directly per my comment to that answer).

edited Sep 17, 2019 at 13:32

answered Sep 17, 2019 at 13:28

chepner

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2 Comments

Kevin Troy Over a year ago

The call to str() doesn't do anything here -- it's passed a string and returns the same string

chepner Over a year ago

True; I'll adjust that.

Barb · Accepted Answer · 2019-09-17 13:52:08Z

0

To add to the above answers you can validate the input as an integer:

while True:
    try:
       userInput = int(input('Enter a number:> '))       
    except ValueError:
       print("Not an integer! Try again.")
       continue
    else:
       return userInput 
       break

answered Sep 17, 2019 at 13:52

Barb

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