YouTipRef Math Isfinite
## Python math.isfinite() Method
The `math.isfinite()` method is a built-in function in Python's standard `math` module. It is used to determine whether a given number is finite.
A number is considered **finite** if it is neither infinity (positive or negative) nor a NaN (Not a Number) value.
---
### Introduction
In scientific computing, data analysis, and general programming, you often encounter special floating-point values such as positive infinity (`inf`), negative infinity (`-inf`), and Not-a-Number (`NaN`).
The `math.isfinite()` method provides a reliable, built-in way to validate your numeric data before performing mathematical operations that might otherwise fail or produce invalid results.
* **Python Version Added:** 3.2
---
### Syntax
```python
import math
math.isfinite(x)
```
#### Parameters
| Parameter | Type | Description |
| :--- | :--- | :--- |
| **x** | `float` or `int` | **Required.** The numeric value to check. |
> **Note:** If `x` is not a number (e.g., a string, list, or dictionary), the method will raise a `TypeError`.
#### Return Value
* Returns **`True`** if `x` is a finite number (neither infinity nor NaN).
* Returns **`False`** if `x` is positive infinity, negative infinity, or NaN.
---
### Code Examples
The following example demonstrates how to use `math.isfinite()` to check various types of numeric values, including standard integers, floats, infinities, and NaN.
```python
import math
# Check standard finite numbers
print(math.isfinite(2000)) # Output: True
print(math.isfinite(-45.34)) # Output: True
print(math.isfinite(+45.34)) # Output: True
print(math.isfinite(0.0)) # Output: True
# Check infinity constants from the math module
print(math.isfinite(math.inf)) # Output: False
print(math.isfinite(-math.inf)) # Output: False
# Check parsed string representations of NaN and Infinity
print(math.isfinite(float("nan"))) # Output: False
print(math.isfinite(float("inf"))) # Output: False
print(math.isfinite(float("-inf"))) # Output: False
```
#### Output:
```text
True
True
True
True
False
False
False
False
False
```
---
### Considerations and Best Practices
1. **Handling Non-Numeric Types:**
If you pass a non-numeric type to `math.isfinite()`, Python will raise a `TypeError`. If your input data might contain non-numeric types, wrap the call in a `try-except` block:
```python
import math
value = "123" # String type
try:
is_finite = math.isfinite(value)
except TypeError:
print("The input is not a valid numeric type.")
```
2. **Difference from `math.isinf()` and `math.isnan()`:**
* `math.isfinite(x)` returns `True` only if the number is a normal, valid real number.
* `math.isinf(x)` returns `True` *only* if the number is positive or negative infinity.
* `math.isnan(x)` returns `True` *only* if the number is NaN.
Essentially, `math.isfinite(x)` is equivalent to:
```python
not math.isinf(x) and not math.isnan(x)
```