How To Check If A Variable Is An Integer Or Not?

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Summary: Use the isinstance(var, int) method to check if a variable is an Integer or not. The method checks if a specified object is of a specified type or not. Another method to check if the variable is an integer or not is the is_integer() function which checks if a given float variable holds an integer value or a decimal value.

Problem: Given a variable in a program; how to check if it is an integer or not?

Example: 

def checInt(val):
  #Some function to check if val is an Integer
  
  #if YES:
  return True

  #else
  return False

a = 25
b = 'FINXTER' 
print(checInt(a))
print(checInt(b))

Output:

True
False

Thus, in the above example we need to define a procedure such that when we check if a is an integer then it returns True while for b it should return False.

? Before proceeding further, let me give you a teaser of the solutions that are lined up next. Please have a look at the code given below.

def checInt(val):
  # Method 1
  if (isinstance(val,(int,float)) == True):
    print ("Method 1 Successful!")
  # Method 2
  if (val.is_integer):
    print ("Method 2 Successful!")
  # Method 3
  if (val == round(val)):
    print ("Method 3 Successful!")
  # Method 4
  if (val % 1 == 0):
    print ("Method 4 Successful!")
  
a = 25.0
checInt(a)

Output:

Method 1 Successful!
Method 2 Successful!
Method 3 Successful!
Method 4 Successful!

Now, without further delay let us discuss the various methods to get our desired output.

Method 1: Using isinstance(var, int)

◉ isinstance is a built-in method in Python which returns True when the specified object is an instance of the specified type, otherwise it returns False.

Syntax:

Example:

# Example 1
class Finxter:
  name = "Python"

obj = Finxter()

test = isinstance(obj, Finxter)

print(test)

# Example 2
x = isinstance("Hello Finxter!", (str,float,int))
print(x)

Output:

True
True

Now that we know about the isinstance method, let us check how we can use it to check if the variable is integer or not. Please follow the program given below:

class Finxter(int): pass
x = Finxter(0)

print(isinstance(x, int))

Output:

True

Why We Should Not use “type”?

The usage of type to solve our problem should be avoided because if you subclass int as in the above example, type won’t register the value of the variable as int. Let us have a look at the following piece of code to understand, why using type is not a good option.

class Test(int): pass
x = Test(0)
print(type(x) == int) # False
print(type(x),"is not same as int")

Output:

False
<class '__main__.Test'> is not same as int

✍ A probable workaround for the above issue could be the usage of subclass() which is a built-in function in Python that checks if a given class/object is a subclass of another specified class. Let us have a look at this in a program given below:

class Test(int): pass
x = Test(0)
print(issubclass(type(x), int))

Output:

True

Method 2: Using var.is_integer()

An integer represents only an integer value (no decimal), while float represents numbers that can be integers like 25.0 as well as decimal numbers like 25.75. We can thus call the is_integer() method to check if the float represents an integer.

Let us have a look at the following to get a clear picture.

a = 25.0
b = 25.75
print(a.is_integer())
print(b.is_integer())

Output:

True
False

Method 3: Using round()

A simple approach to check if the given variable is an integer or not can be to check if it is equal to the value when it is rounded. For this purpose, we can use the in-built round() method in Python which returns the nearest integer when no values are passed on to the optional digit argument.

Syntax:

round(number, digits)
  • number represents the number that has to be rounded.
  • digits represent the number of decimals to be used while rounding the number.

Let’s have a look at the following program to check if a variable is an integer or not:

def is_int(value):
  if value == round(value):
    print ('True')
  else:
    print ('False')


a = 25.0
b = 25.75
is_int(a)
is_int(b)

Output:

True
False

Method 4: A Quick Hack

Here’s a quick hack to check if the given variable is an integer or not. All we need is a simple modulo operator as shown below.

def is_int(value):
  if value%1 == 0 :
    print ('True')
  else:
    print ('False')

a = 25.0
b = 25.75
is_int(a)
is_int(b)

Output:

True
False

Caution: This just a quick workaround and should not be considered as a first choice while checking if a variable is an integer or not.

Method 5: Using try And except Block

Another approach to our problem is to use the try and except block. Instead of directly checking if the value is an integer or not, we consider it to be an integer initially and catch the exception if it isn’t. If this sounds confusing, please have a look at the program below which will make things easy for you.

def is_int(value):
  try:
    return int(value)==value
  except ValueError:
    return False

a = 25.0
b = 25.75
c = "FINXTER"

print(is_int(a))
print(is_int(b))
print(is_int(c))

Output:

True
False
False

Method 6: Using str.isdigit() Method

If you want to check if a variable has an integer string value or not, then the str.isdigit() method can be very useful. As the name suggests, str.isdigit() returns True if all the characters present in the string are digits. Otherwise, it returns False.

☠ Alert:

  • It only works if the str is string. Integers do not have an isdigit method.
  • isdigit() returns False for negative integers

Now, let us have a look at a working example of the isdigit() method to check if a variable is an integer string or not.

def is_int(value):
  return str.isdigit(value)

a = "25"
b = "FINXTER"

print(is_int(a))
print(is_int(b))

Output:

True
False

Conclusion

The key points that we learned in this article were:

  • Using the isinstance() method.
  • Why type should be avoided in solving our problem.
  • Using the issubclass() method.
  • Using the is_integer() method.
  • Using the round() function.
  • Using try and except blocks to solve our problem.
  • Using the isdigit() method.

I hope you after reading this article you can check if a variable is an integer or not with ease. Please subscribe and stay tuned for more interesting articles.

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