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`

.

Table of Contents

## 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

Argument | `number` | Numerical value—in most cases a float. |

Argument | `ndigits` | (Optional) Precision in number of decimal digits. Default 0. |

Return Value | `number` | Numerical value rounded to the given precision. |

## Video round()

## 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[0]) 3 >>> np.round(lst[0]) 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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