# Numpy – Check If a Number is Real

In this tutorial, we will look at how to check if a number in a Numpy array is a real number or not with the help of some examples. Real numbers in mathematics are numbers that do not have an imaginary part, for example – `21`, `4.31`, `2 + 0j`, etc.

## How to test for a real number in a Numpy array?

You can use the `numpy.isreal()` function to check (element-wise) if values in a Numpy array are real or not. The following is the syntax –

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```# test for real numbers - pass scaler value or numpy array
np.isreal(a)```

The `numpy.isreal()` function essentially tests (element-wise) whether the imaginary part of the number is zero or not. It returns a boolean array if you pass an array and if you pass a scaler value, it returns a boolean value.

## Examples

Let’s now look at some examples of using the above function to test for real numbers.

### Example 1 – Check if a number is real or not using `numpy.isreal()`

First, let’s pass scaler values to the `numpy.isreal()` function.

Let’s apply the `numpy.isreal()` function on three scaler values – a real number, a complex number with a non-zero imaginary part, and a complex number with the imaginary part as 0.

```import numpy as np

# check if real
print(np.isreal(14))
print(np.isreal(2 + 4j))
print(np.isreal(2 + 0j))```

Output:

```True
False
True```

We get `True` as the output for the real number 14 and the complex number having 0 as its imaginary part. And we get `False` as the output for the complex number with a non-zero imaginary part.

Note that here, even though the value `2 + 0j` is of `complex` type, the `numpy.isreal()` function returns it as a real number (since its imaginary part is 0 which essentially makes it a real number).

If, on the other hand, you want to check whether the value is not of `complex` type, use the `numpy.isrealobj()` function.

```# check if not complex type object
print(np.isrealobj(14))
print(np.isrealobj(2 + 4j))
print(np.isrealobj(2 + 0j))```

Output:

```True
False
False```

We get `True` as the output for the real number 14 and `False` as the output for both the complex type values (irrespective of whether the imaginary part is 0 or not).

### Example 2 – Element-wise check for real number in a Numpy array using `numpy.isreal()`

If you apply the `numpy.isreal()` function on an array, it will return a boolean array containing `True` for the values that are real numbers and `False` for the other values.

Let’s create a 1-D array and apply the `numpy.isreal()` function to it.

```# create a numpy array
ar = np.array([1, 2+3j, 2+0j, 4, 5.7, np.nan, np.inf, 1j, 0+0j])
# element-wise check for real number in ar
np.isreal(ar)```

Output:

`array([ True, False,  True,  True,  True,  True,  True, False,  True])`

We get a boolean array as an output. You can see that in the boolean array we get `True` for only the values that test as a real number in the original array.

## Summary

In this tutorial, we looked at how we can use the `numpy.isreal()` function to check if a number is a real number or not in a Numpy array. Keep in mind that this function checks whether the imaginary part of the number is zero or not. If you want to check whether the number is not of `complex` type, use the `numpy.isrealobj()` function instead.

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