Table of Contents

## Problem Formulation

Given a string in hexadecimal form:

s = '0xff' # or: s = 'ff'

**How to convert the hex string to an integer in Python?**

For example, you want to convert the hexadecimal string `'0xff'`

to the decimal integer `255`

.

Here are a few other examples:

0x0 --> 0 0x4 --> 4 0x8 --> 8 0x12 --> 18 0x16 --> 22 0x20 --> 32 0x24 --> 36 0x28 --> 40

## Hex String to Integer using int() with base 16

To convert a hexadecimal string to an integer, pass the string as a first argument into Python’s built-in `int()`

function. Use `base=16`

as a second argument of the `int()`

function to specify that the given string is a hex number. The `int()`

function will then convert the hex string to an integer with base 10 and return the result.

Here’s a minimal example:

>>> int('0xff', base=16) 255

## Examples

And here’s how you can convert the additional examples shown above:

>>> int('0x0', base=16) 0 >>> int('0x4', base=16) 4 >>> int('0x8', base=16) 8 >>> int('0x12', base=16) 18 >>> int('0x16', base=16) 22 >>> int('0x20', base=16) 32 >>> int('0x24', base=16) 36 >>> int('0x28', base=16) 40

You actually don’t need to use the prefix `'0x'`

because your second argument already defines unambiguously that the given string is a hexadecimal number:

>>> int('0', base=16) 0 >>> int('4', base=16) 4 >>> int('8', base=16) 8 >>> int('12', base=16) 18 >>> int('16', base=16) 22 >>> int('20', base=16) 32 >>> int('24', base=16) 36 >>> int('28', base=16) 40

However, skipping the base but leaving the prefix raises a `ValueError: invalid literal for int() with base 10: '0x28'`

:

>>> int('0x28') Traceback (most recent call last): File "<pyshell#19>", line 1, in <module> int('0x28') ValueError: invalid literal for int() with base 10: '0x28'

It assumes that the input string is in base 10 when in fact, it isn’t.

? **Note**: Even though passing a prefixed string `'0x...'`

into the `int()`

function is unambiguous, Python’s `int()`

function doesn’t accept it if you don’t also define the base. This may be fixed in future versions!

In fact, you can specify the base argument as 0 to switch on base guessing—which should be the default behavior anyway!

## Base Guessing

You can pass a prefixed string `'0x...'`

into the `int()`

function and set the base to 0 to switch on base guessing in Python. This uses the prefix to determine the base automatically—without you needing to set it to `16`

. Yet, you still have to set it to `0`

so the benefit is marginal in practice.

>>> int('0x9', base=16) 9 >>> int('0x9', base=0) 9 >>> int('0x9', 0) 9

## Converting Hex Literals to Int

If you don’t have a hex string but a hex number—called a * literal*—such as

`0xff`

, you don’t even need the `int()`

function because Python will automatically convert it to a decimal number:>>> 0x10 16 >>> 0xff 255

## Background int()

Syntax: int(value [, base]) --> int

Argument | `value` | A Python object to be converted into an integer number. The value object must have an `__int__()` method that returns the associated integer number—otherwise a `TypeError` will be raised. |

`base` | An optional integer argument `base` to define the base of the numerical system in the `value` argument. If you set the base, the `value` argument must be a string. The `base` argument determines how the string argument is interpreted. | |

Return Value | `int` | Returns an integer number after converting the input argument `value` using its required `__int__()` method for the conversion. |

Do you still need more background information about Python’s built-in `int()`

function? No problem, read over the related tutorial.

**Related Tutorial:** Python’s Built-in `int()`

Function

## Hex to Int Table

Just for fun, here are the hex to int conversions of the powers of two:

Hexadecimal Literal | Decimal Literal |
---|---|

1 | 1 |

2 | 2 |

4 | 4 |

8 | 8 |

10_{hex} | 16_{dec} |

20_{hex} | 32_{dec} |

40_{hex} | 64_{dec} |

80_{hex} | 128_{dec} |

100_{hex} | 256_{dec} |

200_{hex} | 512_{dec} |

400_{hex} | 1024_{dec} |

800_{hex} | 2048_{dec} |

1000_{hex} | 4096_{dec} |

2000_{hex} | 8192_{dec} |

4000_{hex} | 16,384_{dec} |

8000_{hex} | 32,768_{dec} |

10000_{hex} | 65,536_{dec} |

While working as a researcher in distributed systems, Dr. Christian Mayer found his love for teaching computer science students.

To help students reach higher levels of Python success, he founded the programming education website Finxter.com. He’s author of the popular programming book Python One-Liners (NoStarch 2020), coauthor of the Coffee Break Python series of self-published books, computer science enthusiast, freelancer, and owner of one of the top 10 largest Python blogs worldwide.

His passions are writing, reading, and coding. But his greatest passion is to serve aspiring coders through Finxter and help them to boost their skills. You can join his free email academy here.