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:\Users\Tyagiji\Documents\Python Projects\TRyinrg differet\experiments.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.

the error shows that you have not given correct input. Correct input should be `add 1 2` have you given this input ? — Deepak Tripathi, Oct 15 '22 at 07:23
`isinstance(splited[1],int) == True` will always fail as you've split a string, so `splited[1]` is never an integer. Also the `==True` is redundant. — bn_ln, Oct 15 '22 at 07:26
@bn_ln so what can I I do instead of splitting the string and I have also tried ```if isinstance(splited[1],int): ``` — Nishesh Tyagi, Oct 15 '22 at 07:30
Just remove the `str()` typecaste from the line `uinput = str(input())` and now try `uinput.isdigit()` and `uinput.isfloat()` — Swagrim, Oct 15 '22 at 07:34
@Swagrim removed the ``str()`` and i tried ```uinput.isdigit()``` and it works but it doesn't count negative numbers and float. — Nishesh Tyagi, Oct 15 '22 at 07:37

Deepak Tripathi · Accepted Answer · 2022-10-15T07:44:21.117

0

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

edited Oct 15 '22 at 07:44

answered Oct 15 '22 at 07:36

Deepak Tripathi

3,175
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I tried this and typed add 1 2 it says ```add not in ['add', 'subtract', 'multiply', 'divide']``` – Nishesh Tyagi Oct 15 '22 at 07:40
Yes, this answer has a bug in it. Change `if op not in operators:` to `if not op:` – bn_ln Oct 15 '22 at 07:44
I have changed it , Now check @NisheshTyagi . The condition should be before getting the operator – Deepak Tripathi Oct 15 '22 at 07:44
you should really test your answer before posting it – bn_ln Oct 15 '22 at 07:45
1

@bn_ln Sorry for that , I have tested for failure cases thatwhy success test cases skipped. – Deepak Tripathi Oct 15 '22 at 07:48
@DeepakTripathi when i type add 1 3 it works like it did with ```isdigit()``` but it doesnt work for float it gives ```invalid literal for int() with base 10: '1.6'``` it gives the same for a string ```invalid literal for int() with base 10: 'b'``` it should give "please enter a number" – Nishesh Tyagi Oct 15 '22 at 07:49
For that only , I have said you can play with data type, `map(int, splited[1:])` to `map(float, splitted[1:])` . – Deepak Tripathi Oct 15 '22 at 07:53

score 0 · Answer 2 · answered Oct 15 '22 at 08:40

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

Check if the input is integer float or string in python

2 Answers2