In this article, we will check whether the given value is NaN or Infinity. This can be done using the math module. Let’s see how to check each value in detail.
Check for NaN values in Python
NaN Stands for “Not a Number” and it is a numeric datatype used as a proxy for values that are either mathematically undefined or cannot be represented. There are various examples of them like:
- 0/0 is undefined and NaN is used for representing it.
- Sqrt(-ve number) cannot be stored as a real number so NaN is used for representing it.
- Log(-ve number) cannot be stored as a real number so NaN is used for representing it.
- Inverse sin or Inverse cos of a number < -1 or number > 1 is also NaN.
- 0 * inf also leads to NaN.
Since NaN is a type in itself It is used to assign variables whose values are not yet calculated.
Using math.isnan() to Check for NaN values in Python
To check for NaN we can use math.isnan() function as NaN cannot be tested using == operator.
Python3
import mathx = math.nanprint(f"x contains {x}")# checks if variable is equal to NaNif(math.isnan(x)): print("x == nan")else: print("x != nan") |
x contains nan x == nan
Using np.isnan() to Check for NaN values in Python
Here, we use Numpy to test if the value is NaN in Python.
Python3
import numpy as npx = float("nan")print(f"x contains {x}")# checks if variable is equal to NaNif(np.isnan(x)): print("x == nan")else: print("x != nan") |
Output:
x contains nan x == nan
Using pd.isna() to Check for NaN values in Python
Here, we use Pandas to test if the value is NaN in Python.
Python3
import pandas as pdx = float("nan")x = 6print(f"x contains {x}")# checks if variable is equal to NaNif(pd.isna(x)): print("x == nan")else: print("x != nan") |
Output:
x contains nan x != nan
Check for Infinite values in Python
Using math.isinf() to Check for Infinite values in Python
To check for infinite in python the function used is math.isinf() which only checks for infinite. To distinguish between positive and negative infinite we can add more logic that checks if the number is greater than 0 or less than 0. The code shows this in action.
Python3
import math# Function checks if negative or# positive infinite.def check(x): if(math.isinf(x) and x > 0): print("x is Positive inf") elif(math.isinf(x) and x < 0): print("x is negative inf") else: print("x is not inf")# Creating inf using math module.number = math.infcheck(number)number = -math.infcheck(number) |
x is Positive inf x is negative inf
Using np.isneginf() to Check for Infinite values in Python
Numpy also exposes two APIs to check for positive and negative infinite. which are np.isneginf() and np.isposinf().
Python3
# pip install numpyimport numpy as npprint(np.isneginf([np.inf, 0, -np.inf]))print(np.isposinf([np.inf, 0, -np.inf])) |
Output
[False False True] [ True False False]
Check for finite values in Python
Using math.isfinite() to Check for finite values in Python
Checking for finite values finds values that are not NaN or infinite. Negating this function combines both the check for NaN and inf values into a single function call.
Python3
import mathcandidates = [1, math.nan, math.inf, 1/3, 123]for value_to_check in candidates: print(f"{value_to_check} is NaN or inf: {not math.isfinite(value_to_check)}") |
1 is NaN or inf: False nan is NaN or inf: True inf is NaN or inf: True 0.3333333333333333 is NaN or inf: False 123 is NaN or inf: False
Using the decimal module:
Approach:
Import the decimal module.
Create a Decimal object from the value.
Use the Decimal.is_infinite() method to check if the value is infinity.
Use the Decimal.is_nan() method to check if the value is NaN.
Python3
import decimal# Positive infinityx = decimal.Decimal('Infinity')if x.is_infinite(): print("x is Positive inf") if x.is_finite() and x < 0: print("x is negative inf") |
x is Positive inf
Time Complexity: O(1)
Space Complexity: O(1)
