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LAST UPDATED: NOVEMBER 1, 2019

Python Math functions - isinf(), isfinite(), and isnan()

    In previous posts, we discussed a variety of math module functions. Continuing the same, we will discuss the below-mentioned math module functions.

    1. isfinite

    2. isinf

    3. isnan

    These methods are built-in and are present in the math module. They can be accessed and used after importing the math module and referencing it with the help of the dot operator.


    1. The isfinite method

    It takes one argument and returns True if the argument is a valid python number. This number could be positive or negative. If the parameter passed is infinite or Nan (Not a number), it returns False.

    Following is the sntax of the isfinite method,

    math.isfinite(number)

    If no value has been provided to the isfinite function, it throws TypeError.


    Time for an example:

    The below example demonstrates different cases (values) that could be passed to the isfinite method.

    import math
     
    print(math.isfinite(12))
    print(math.isfinite(0.0))  # Python considers 0.0 as finite number
    print(math.isfinite(0/12))
    print(math.isfinite(0.0/21))
    print(math.isfinite(-79))
    print(math.isfinite(-79.89))
    print(math.isfinite(float('nan'))) 
    print(math.isfinite(math.inf))
    print(math.isfinite('{'))   # When a string is passed (error)
    print(math.isfinite())   # When no parameter is passed (error)

    Output:

    True
    True
    True
    True
    True
    True
    False
    False
    Traceback (most recent call last):
    
      File "<ipython-input-197-511869dbfa73>", line 9, in <module>
        print(math.isfinite('{'))
    
    TypeError: must be real number, not str

    Note: Don't confuse this with numpy module's isfinite method.




    2. The isinf method

    The isinf method of the math module takes one argument and checks if the number is infinite. If yes, it returns True and it returns False if the number passed as argument is finite or a Nan (Not a number).

    In case no parameter is passed to the function, it returns TypeError.

    Following is the syntax of the isinf method,

    math.isinf(argument)

    Time for an example:

    import math
     
    print(math.isinf(12))
    print(math.isinf(0.0))  # Python considers 0.0 as finite number
    print(math.isinf(0/12))
    print(math.isinf(0.0/21))
    print(math.isinf(-79))
    print(math.isinf(-79.89))
    print(math.isinf(math.inf))  # When infinity is passed as an argument
    print(math.isinf())   # When no parameter is passed


    Output:

    False
    False
    False
    False
    False
    False
    True
    Traceback (most recent call last):
    
      File "<ipython-input-199-9781ae1653ba>", line 10, in <module>
        print(math.isinf())
    
    TypeError: isinf() takes exactly one argument (0 given)

    Note: Don't confuse this with numpy module's isinf method.




    3. The isnan method

    This method takes one argument and checks if it Nan(not a number). If yes, it returns True and if the argument passed is a valid Python number, it returns False. If no parameter is passed to the isnan method, it throws TypeError.

    Following is the syntax of the isnan method,

    math.isnan(argument)

    Time for an example:

    import math
     
    print(math.isnan(12))
    print(math.isnan(0.0))  # Python considers 0.0 as finite number
    print(math.isinf(0/12))
    print(math.isnan(-79))
    print(math.isnan(-79.89))
    print(math.isnan(math.pi))
    print(math.isnan(float('nan')))   # Passing nan to the isnan method 
    print(math.isnan())  # No parameter passed


    Output:

    False
    False
    False
    False
    False
    False
    True
    Traceback (most recent call last):
    
      File "<ipython-input-204-849cf7490bda>", line 10, in <module>
        print(math.isnan())
    
    TypeError: isnan() takes exactly one argument (0 given)

    Note: Don't confuse this method with numpy.isnan method




    Conclusion

    In this post, we understood three more built-in methods from the math module namely isfinite(), isinf() and isnan(). These methods come in handy while manipulating numbers. Don't forget to execute these Python programs on your IDE. Meddle with the input to see how the output changes.

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    I love writing about Python and have more than 5 years of professional experience in Python development. I like sharing about various standard libraries in Python and other Python Modules.
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