Check if the input is integer float or string in python

Question

I am a beginner in python and I am currently working on a calculator not like this:
Enter Something: add
"Enter 1 number : 1"
"Enter 2 number : 3"
The answer is 5
not like that or using eval()
I Want to create a calculator where they input something like this: "add 1 3" and output should be 4.
but I have to check that the first word is a string 2nd is a integer or float and 3rd is also number
I have created a script but I have one problem that I don’t know how to check if the input is a integer or string or float I have used isdigit() it works but it doesn’t count negative numbers and float as a number I have also used isinstance() but it doesn’t work and thinks that the input is a integer even when its a string and I don’t know how to use the try and except method on this script

while True:
    exitcond = ["exit","close","quit"]
    operators =["add","subtract","multiply","divide"]
    uinput = str(input())
    lowereduin = uinput.lower()
    splited = lowereduin.split(" ")
    if lowereduin in exitcond:
        break
    if splited[0] == operators[0]:
        if isinstance(splited[1],int) == True:
            if isinstance(splited[2] , int) == True:
                result = int(splited[1]) + int(splited[2])
                print(result)
            else:
                print("enter a number")
        else:
            print("enter a number")

and when I run this script and type add 1 3 its says enter a number and when I only type add its give this error

Traceback (most recent call last):
  File "C:UsersTyagijiDocumentsPython ProjectsTRyinrg differetexperiments.py", line 11, in <module>
    if isinstance(splited[1],int) == True:
IndexError: list index out of range

Can someone tell me what’s this error and if this doesn’t work can you tell me how to use try: method on this script.

Asked By: Nishesh Tyagi

||

Source

Answer 1

You can try the following approach and play with type checking

import operator

while True:
    exitcond = ["exit","close","quit"]
    operators ={"add": operator.add,"subtract":operator.sub,"multiply": operator.mul,"divide":operator.truediv}
    uinput = str(input())
    lowereduin = uinput.lower()
    splited = lowereduin.split(" ")
    if lowereduin in exitcond or (len(splited) !=3):
        break
    try:
        if splited[0] not in operators.keys():
            raise ValueError(f"{splited[0]} not in {list(operators.keys())}")
        op = operators.get(splited[0])
        val = op(
            *map(int, splited[1:])
        )
        print(val)
    except (ValueError, ZeroDivisionError) as err:
        print(err)
        break

Answered By: Deepak Tripathi

Answer 2

Building on Deepak’s answer. A dictionary of operator names to functions is a good approach. And you can add to splits until you have enough numbers to proceed.

import operator as op
while True:
    exitcond = ["exit","close","quit"]
    operators = {"add": op.add,"subtract": op.sub, "multiply": op.mul, "divide": op.truediv}
    splits = str(input()).lower().split()
    if any(part in exitcond for part in splits):
        break

    while len(splits) < 3:
        splits.append(input('Enter number: '))

    try:
        print(operators[splits[0]](*map(lambda x: float(x.replace(',','')), splits[1:3])))
    except ZeroDivisionError:
        print("Can't divide by 0")
    except:
        print('Expected input: add|subtract|multiply|divide [number1] [number2] -- or -- exit|quit|close')

Things to note, the lambda function removes all commas , as they fail for floats, and then converts the all number strings to floats. So, the answer will always be a float, which opens the can of worms that add 1.1 2.2 won’t be exactly 3.3 due to the well documented issues with floating point arithmatic and computers

Answered By: bn_ln

Check if the input is integer float or string in python

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