# Python round() — A Simple Guide with Video

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Python’s built-in `round()` function takes two input arguments: a `number` and an optional `precision` in decimal digits. It rounds the number to the given precision and returns the result. The return value has the same type as the input number—or integer if the `precision` argument is omitted. Per default, the precision is set to 0 digits, so `round(3.14)` results in `3`.

## Usage

Learn by example! Here are some examples of how to use the `round()` built-in function.

```>>> round(3.14)
3
>>> round(3.14, ndigits=1)
3.1
>>> round(3.13, ndigits=-1)
0.0
>>> round(4458.1242, ndigits=-1)
4460.0
>>> round(3.14159, ndigits=3)
3.142```

## Syntax round()

You can use the `round()` method as follows:

```Syntax:
round(number, precision)    # rounds the number to the given precision and returns the result ```

## Interactive Shell Exercise: Understanding round()

Consider the following interactive code:

Exercise: Guess the output before running the code.

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## How to Round All Values in a List in Python?

Problem Formulation: Given a list of numerical values. How to round all values in the list to a given precision?

To round all values of a list, use list comprehension `[round(x, ndigits=precision) for x in list]` to apply the `round()` function to all values in the list and place the resulting numerical values into a new list:

```lst = [3.14, 3.44444, 4.424242]
rounded = [round(x, ndigits=2) for x in lst]
print(rounded)
# [3.14, 3.44, 4.42]
```

## Python round() vs NumPy round()

Python’s `round()` function rounds a single numerical value to a single rounded value, given a certain precision. NumPy‘s `np.round()` function can do the same but more: if you pass an array or list of numerical values, it’ll round all values in the passed array-like data structure. In addition to that, in contrast to Python’s built-in `round()` function that returns an integer if no precision argument is given, the function `np.round()` always returns a float.

```>>> import numpy as np
>>> lst = [3.14, 3.44444, 4.424242]
>>> round(lst)
3
>>> np.round(lst)
3.0
>>> np.round(lst)
array([3., 3., 4.])```

## Summary

Python’s built-in `round()` function takes two input arguments:

• a `number`, and
• an optional `precision` in decimal digits.

It rounds the number to the given precision and returns the result.

```>>> round(3.14, ndigit=1)
3.1
>>> round(3.14)
3```

The return value has the same type as the input number—or integer if the `precision` argument is omitted. Per default, the precision is set to 0 digits, so `round(3.14)` results in `3`.

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