Checking whether a variable is an integer or not [duplicate]

Answer 1

If you want to check that a string consists of only digits, but converting to an int won't help, you can always just use regex.

import re
x = "01234"
match = re.search("^\d+$", x)
try: x = match.group(0)
except AttributeError: print("not a valid number")

Result: x == "01234"

In this case, if x were "hello", converting it to a numeric type would throw a ValueError, but data would also be lost in the process. Using a regex and catching an AttributeError would allow you to confirm numeric characters in a string with, for instance, leading 0's.

If you didn't want it to throw an AttributeError, but instead just wanted to look for more specific problems, you could vary the regex and just check the match:

import re
x = "h01234"
match = re.search("\D", x)
if not match:
    print("x is a number")
else:
    print("encountered a problem at character:", match.group(0))

Result: "encountered a problem at character: h"

That actually shows you where the problem occurred without the use of exceptions. Again, this is not for testing the type, but rather the characters themselves. This gives you much more flexibility than simply checking for types, especially when converting between types can lose important string data, like leading 0's.

Answer 2

Here's a summary of the different methods mentioned here:

• int(x) == x
• try x = operator.index(x)
• isinstance(x, int)
• isinstance(x, numbers.Integral)

and here's how they apply to a variety of numerical types that have integer value:

You can see they aren't 100% consistent. Fraction and Rational are conceptually the same, but one supplies a .index() method and the other doesn't. Complex types don't like to convert to int even if the real part is integral and imaginary part is 0.

(np.int8|16|32|64(5) means that np.int8(5), np.int32(5), etc. all behave identically)

Answer 3

Rather than over complicate things, why not just a simple

if type(var) is int:

Answer 4

why not just check if the value you want to check is equal to itself cast as an integer as shown below?

def isInt(val):
    return val == int(val)

Answer 5

I can check if the number is integer include number like 7.0

def is_int(x):
    if x - round(x) == 0 :
        return True
    else:
        return False

Answer 6

In the presence of numpy check like ..

isinstance(var, numbers.Integral)

.. (slow) or ..

isinstance(var, (int, long, np.integer))

.. in order to match all type variants like np.int8, np.uint16, ...

(Drop long in PY3)

Recognizing ANY integer-like object from anywhere is a tricky guessing game. Checking

var & 0 == 0 

for truth and non-exception may be a good bet. Similarly, checking for signed integer type exclusively:

var ^ -1 ==  -var - 1