[Tut] How to Convert Octal String to Integer in Python

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How to Convert Octal String to Integer in Python

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Problem Formulation

Given a string in the octal form:

Code:

s = '0o77' # or s = '77'

How to convert the octal string to an integer in Python?

For example, you want to convert the octal string

Code:

'o10'

to the decimal integer

Code:

8

.

Here are a few other examples:

Octal String |
Decimal

Code:

'0o0'

|
0

Code:

'0o4'

|
4

Code:

'0o10'

|
8

Code:

'0o14'

|
12

Code:

'0o20'

|
16

Code:

'0o77'

|
63

Code:

'0o77777'

|
32767

Oct String to Integer using int() with Base 8

To convert an octal string to an integer, pass the string as a first argument into Python’sbuilt-in

Code:

int()

function. Use

Code:

base=8

as a second argument of the

Code:

int()

function to specify that the given string is an octal number. The

Code:

int()

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

Here’s a minimal example:

Code:

>>> int('0o77', base=8) 63

Examples

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

Code:

>>> int('0o0', base=8) 0 >>> int('0o4', base=8) 4 >>> int('0o10', base=8) 8 >>> int('0o14', base=8) 12 >>> int('0o20', base=8) 16 >>> int('0o77', base=8) 63 >>> int('0o77777', base=8) 32767

You actually don’t need to use the prefix

Code:

'0o'

because your second argument already defines unambiguously that the given string is an octal number:

Code:

>>> int('0', base=8) 0 >>> int('4', base=8) 4 >>> int('10', base=8) 8 >>> int('14', base=8) 12 >>> int('20', base=8) 16 >>> int('77', base=8) 63 >>> int('77777', base=8) 32767

However, skipping the base but leaving the prefix raises a

Code:

ValueError: invalid literal for int() with base 10: '0o77'

:

Code:

>>> int('0o77') Traceback (most recent call last): File "<pyshell#16>", line 1, in <module> int('0o77') ValueError: invalid literal for int() with base 10: '0o77'

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

Note: Even though passing a prefixed string

Code:

'0o...'

into the

Code:

int()

function is unambiguous, Python’s

Code:

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 to switch on base guessing—which should be the default behavior anyway!

Base Guessing

You can pass a prefixed string

Code:

'0o...'

into the

Code:

int()

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

Code:

16

. Yet, you still have to set it to so the benefit is marginal in practice.

Code:

>>> int('0o7', base=8) 7 >>> int('0o7', base=0) 7 >>> int('0o7', 0) 7

Converting Octal Literals to Int



If you don’t have an octal string but a octal number—called a literal—such as

Code:

0xff

, you don’t even need the

Code:

int()

function because Python will automatically convert it to a decimal number:

Code:

>>> 0o743 483 >>> 0o7 7 >>> 0o10 8

Background int()

Code:

Syntax: int(value [, base]) – > int

Argument |

Code:

value

|
A Python object to be converted into an integer number. The value object must have an

Code:

__int__()

method that returns the associated integer number—otherwise a

Code:

TypeError

will be raised.

|

Code:

base

|
An optional integer argument

Code:

base

to define the base of the numerical system in the

Code:

value

argument. If you set the base, the

Code:

value

argument must be a string. The

Code:

base

argument determines how the string argument is interpreted.

Return Value |

Code:

int

|
Returns an integer number after converting the input argument

Code:

value

using its required

Code:

__int__()

method for the conversion.



Do you still need more background information about Python’s built-in

Code:

int()

function? No problem, read over the related tutorial.

Related Tutorial: Python’s Built-in

Code:

int()

Function