How to find the type of a variable given by the user?

Question

I would like to ask the user to type something and find out what kind of what he wrote. So far I only know the input(), but the input() only returns the type String. If I put int(input()) or float(input()) fall into the same problem:

I can’t do:

n = input()  
if n == int:  
  print('Tente novamente')  

and neither:

n = int(input())  
if n == str:  
  print('Tente novamente') 

Because I have already specified the type of the variable. How do I make the program discover the type so that I perform the condition based on her type?

Answer 1

Even if he type 1 or 1.0 will be string anyway, a string can be numerically formatted normally, just because 1 is a number doesn’t mean his type will be int.

What you can do is use two regex to detect which format the string resembles and then do the cast, for example:

import re

entrada = input()

if re.match('^\d+$', entrada):
    entrada = int(entrada)
elif re.match('^\d+\.\d+$', entrada):
    entrada = float(entrada)

print(type(entrada), entrada)

A regex ^\d+$ of the first if will search from start to end of string if it has number format, no point.

A regex ^\d+\.\d+$ of the first if will search from the beginning to the end of the string starting with numeric format until it reaches a point, as soon as it reaches the point will look for the number after it, if it occurs the match will enter the if

Should you not recognize any he will print as string even

---

About Python 2.7

Just for the record, in Python version 2.7 input() evaluated the content on its own (as if "val"), so if you did a script like this:

entrada = input()

print type(entrada), entrada

• When the input was 1 would return: <type 'int'> 1

• When the input was 1.0 would return: <type 'float'> 1.0

• When the input was "1" would return: <type 'str'> "1"

So the equivalent of input() of Python 3 to the Python 2 actually would be the raw_input()

Answer 2

use the isinstance() function. Ex, I want to check something the user typed, if it’s an integer to select some option, just:

valor = input("Digite um valor inteiro") // usuario digita "a"
print(isinstance(valor, int) // Saida = False

Of course the value that the user type will always be string, but with this function it is easier to understand for conversion or posteior conversion.

Answer 3

Another simple way is to use the ast.literal_eval.

• Eval vs Ast.literal_eval: what are the differences?

Thus, you do not open security loopholes using the function eval, or need to predict all input formats with regular expressions.

import ast

while True:
    entrada = input('Entre com alguma coisa:')
    valor = ast.literal_eval(entrada)
    print(type(valor))

^{See working on Repl.it}

The result would be something like:

>>> Entre com alguma coisa: 1
<class 'int'>
>>> Entre com alguma coisa: 3.14
<class 'float'>
>>> Entre com alguma coisa: 1,2,3
<class 'tuple'>
>>> Entre com alguma coisa: [1,2,3]
<class 'list'>
>>> Entre com alguma coisa: '1'
<class 'str'>
>>> Entre com alguma coisa: "1"
<class 'str'>

Answer 4

The answer is in the question. There’s nothing to do. You will always know the type of the value, no matter how it is obtained and you will know the type of the variable at that time. In fact languages like Python do not have variable types, just a label saying what type it is representing at that time.

If the code already knows what the guy is, there’s no reason to find anything.

If you are using a function that receives a value that can be of several types then you can use the function type() to identify the type of that object.

Answer 5

Colleague, using the Eval() method it is possible to take and interpret the value of the data inserted in the variable. Example:

numero = input()

try:
    if type(eval(numero)) == type(1):
        print("tipo inteiro")
    elif type(eval(numero)) == type(1.0):
        print("tipo real")
    else:
        print('não é um tipo numérico, %s' % type(numero))
except NameError as n:
    print('não é um tipo numérico, %s' % type(numero))

Maybe this will be simpler. Lazy way mode.