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Check for NaN values in Python

# Check for NaN values in Python

David Y.

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I sometimes see the value NaN (Not a Number) when working with floats in Python. How can I check whether a given value is NaN?

## The Solution

The best way to do this is by using the `isnan()` function from Python’s built-in `math` library:

Click to Copy
```.css-3i4pd0{position:relative;color:inherit;-webkit-transition:box-shadow 0.3s;transition:box-shadow 0.3s;will-change:box-shadow;outline:0;display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-direction:column;-ms-flex-direction:column;flex-direction:column;z-index:9;}.css-3i4pd0:hover,.css-3i4pd0:focus{cursor:pointer;}.css-3i4pd0:hover .e1fliqfg1,.css-3i4pd0:focus .e1fliqfg1{fill:#e1567c;cursor:pointer;}import math

nan = float('nan')
zero = 0
one = 1

print(math.isnan(nan))  # will print True
print(math.isnan(zero))  # will print False
print(math.isnan(one))  # will print False
```

Note that `isnan()` will throw a `TypeError` if given a non-numeric value. Thus, a more robust implementation might look like this:

Click to Copy
```import math

def is_nan(value):
try:
return math.isnan(value)
except TypeError:
return False

nan = float('nan')
zero = 0
one = 1
hello = "Hello!"

print(is_nan(nan))  # will print True
print(is_nan(zero))  # will print False
print(is_nan(one))  # will print False
print(is_nan(hello))  # will print False
```
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