Checking whether a variable is an integer or not

python

type-checking

polymorphism

try-except

byNikita Barsukov·Oct 11, 2024

Confirm if a variable is an integer with Python's isinstance() function:

is_integer = isinstance(42, int)  # Returns True for integers "by nature"

Clear-cut and effective, it differentiates integers (int) from other types such as float or str.

For a numeric entity that's covertly integral expressed as a float, you can verify using:

is_integer = variable.is_integer() if isinstance(variable, float) else isinstance(variable, int)

Going beyond basics

Polymorphism: Python's wildcard

Polymorphism allows Python to treat any object that has integer-like behaviour as an integer.

Safety net: try-except

You can safely execute code and handle any unexpected bare-thumb types using a try-except clause:

try:
    # checking if variable can slip into integer's skin with no changes
    is_integer = int(variable) == variable
except (TypeError, ValueError):
    is_integer = False # it was a trap, deny everything

Dealing with antiquities: Python 2.x

In the Python 2.x world, long type was considered an integer:

is_integer = isinstance(variable, (int, long)) # embracing both old and new folks

Code in disguise: Subclassing and abstract base

int can be extended or abstract base classes can be used (numbers.Integral) for creating new numeric types:

from numbers import Integral

class MyInt(int): # be anything, even an integer!
    pass

is_integer = isinstance(MyInt(5), Integral) # Yes, MyInt instances can "int"eract

An exception with integer's badge: operator.index

operator.index method allows you to inspect whether an object can be fed to an integer:

import operator

try:
    index = operator.index(variable)
    is_integer = True # success! we have a convert
except TypeError:
    is_integer = False # no luck, move on

Refining the Integer Check

Avoid type checks: Design matters!

Strategical code design can ward off superfluous type checks:

def process_number(num: int):
    # Designing code like this implies num should be an integer.
    # Violators may be subjected to righteous fury of error messages.
    pass