What Data Type Is NaN Python?


Larry Thompson

NaN, short for “Not a Number,” is a special floating-point value in Python that represents an undefined or unrepresentable result of a mathematical operation. It is commonly used to indicate missing or invalid data in numerical computations. In Python, NaN belongs to the float data type.

NaN as a Floating-Point Value

The NaN value is typically used to represent the result of operations that are mathematically undefined or don’t produce a valid numerical output. For example, dividing zero by zero or taking the square root of a negative number would result in NaN. When NaN is encountered in calculations, it propagates throughout subsequent operations, acting as a contagious placeholder for any further undefined results.

Distinguishing NaN from Other Values

NaN is distinct from other values because it does not compare equal to any other value, including itself. This means that comparing a variable containing NaN with another variable, even itself, will always yield False.

  • Example:
    • x = float('nan')
    • x == x returns False

To check if a value is NaN, you can use the math.isnan() function from the math module. This function returns True if the argument is NaN and False otherwise.

Detecting NaN:

  • Example:
    • import math
    • x = float('nan')
    • math.isnan(x) returns True

It is important to note that NaN is not the same as None or an empty string. None is a special constant in Python that represents the absence of a value, while NaN represents an undefined numerical result.

NaN in Numeric Operations

When NaN is involved in arithmetic or logical operations, the result is always NaN.

  • Example:
    • x = float('nan')
    • y = 10
    • x + y returns nan
    • x * y returns nan
    • x / y returns nan

Avoiding NaN Issues

To handle NaN values appropriately in your code, you can use conditional statements and error handling techniques. For example, you can check if a value is NaN before performing a calculation and handle it accordingly. Additionally, some libraries and functions provide built-in methods to handle missing or invalid data gracefully.


  • Avoid comparing variables containing NaN directly using the equality operator (==). Instead, use the math.isnan() function.
  • If you encounter NaN values in your calculations, consider investigating the source of these values.

    It could be due to incorrect input data or an error in your calculations that needs to be addressed.

  • Be cautious when using functions that return NaN as part of their normal behavior. Ensure you handle NaN appropriately in your code to avoid unexpected results.

Remember, NaN is a special floating-point value in Python that represents undefined or unrepresentable results. Understanding how NaN behaves and how to handle it appropriately will help you write more robust and reliable numerical code.

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