[Tut] Python bytes() Function

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Python bytes() Function

Python’s built-in

Code:

bytes(source)

function creates an immutable

Code:

bytes

object initialized as defined in the function argument

Code:

source

. A bytes object is like a string but it uses only byte characters consisting of a sequence of 8-bit integers in the range

Code:

0<=x<256

. The returned byte object is immutable—you cannot change it after creation. If you plan to change the contents, use the

Code:

bytearray()

method to create a mutable

Code:

bytearray

object.



Here’s a minimal example that creates a

Code:

byte

from three integers stored in a list:

Code:

>>> bytes([1, 2, 3]) b'\x01\x02\x03'

The prefix

Code:

\x

escape sequence means the next two characters are interpreted as hex character codes. For instance, the hex code

Code:

\x01

is the same as

Code:

chr(0x01)=16*0+1=1

that’s simply a start of heading

Code:

SOH

character. (source, ASCII table)

Code:

Syntax: bytes([source[, encoding[, errors]]])

Argument |

Code:

source

(Optional) |
Allows you to initialize the

Code:

byte

in four different ways (from simple to more complex):

integer –> array has this size and is initialized with 0 bytes:
>>>

Code:

bytes(4)b'\x00\x00\x00\x00'

iterable –> integers in the range

Code:

0 <= x < 256

are initial byte contents:
>>>

Code:

bytes([1, 2, 3])b'\x01\x02\x03'

 string and you provide the encoding (and optionally, errors) arguments –>

Code:

bytes()

converts string to bytes using

Code:

str.encode()

:

Code:

>>> bytes('hi', 'UTF-8')b'hi'

object implementing the buffer interface –> initializes the byte object via a read-only object buffer.

Argument |

Code:

encoding

(Optional) |
The encoding used in case you provide a string argument. Example:

Code:

'UTF-8'

.

Argument |

Code:

errors

(Optional) |
The action to take when the encoding conversion fails. Only makes sense if

Code:

source

argument is a string.

Return Value |

Code:

byte

|
Returns a new object of type byte—a sequence of bytes that is immutable. For a mutable version, consider using the

Code:

bytearray()

function.
Without an optional argument, it returns a byte object with one byte 0:

Code:

>>> bytes()b''

Here are some basic usages of the function:

Code:

Input : bytes(4) Output : b'\x00\x00\x00\x00' Input : bytes([1, 2, 3]) Output : b'\x01\x02\x03' Input : bytes('hi', 'UTF-8') Output : b'hi'

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Create Bytes Object From Single Integer Argument — Examples

The following code shows you how to use the

Code:

bytes()

function on simple integer arguments.

Code:

# Single Integer Input Argument print(bytes()) print(bytes(2)) print(bytes(4)) ''' b'' b'\x00\x00' b'\x00\x00\x00\x00' '''

If you provide only one input argument, it uses this input argument to determine how many bytes should be created. It just uses bytes with value 0, in byte notation

Code:

x00

to fill the

Code:

byte

.

Create Bytes Object From Iterable of Integers — Examples

You can also provide an iterable argument to obtain a new byte object:

Code:

# Iterable Input Argument print(bytes([1, 1, 1])) print(bytes([14])) print(bytes({9, 8, 7})) ''' b'\x01\x01\x01' b'\x0e' b'\x08\t\x07' '''

The iterable must consist of a number of integers between 0 and 256. If you fail to do so, Python will throw a ValueError:

How to Fix “ValueError: byte must be in range(0, 256)”

If you use the

Code:

bytes()

function on an iterable that contains at least one integer greater than the maximum number representable by 8 bits, namely 256, or smaller than 0, Python will throw a

Code:

ValueError: byte must be in range(0, 256)

. You can fix it by ensuring that each number in your iterable can actually be represented by 8 bits and falls into the interval 0 to 256.

Here’s an example of the ValueError where you use a number larger or equal than 256:

Code:

>>> bytes([999]) Traceback (most recent call last): File "<pyshell#15>", line 1, in <module> bytes([999]) ValueError: bytes must be in range(0, 256)

Another example when using a number smaller than 0:

Code:

>>> bytes([-10]) Traceback (most recent call last): File "<pyshell#16>", line 1, in <module> bytes([-10]) ValueError: bytes must be in range(0, 256)

Fix it by modifying the numbers to lie within the interval 0 to 256:

Code:

>>> bytes([255]) b'\xff'

Summary

Python’s built-in function

Code:

bytes()

allows you to initialize the

Code:

byte

in four different ways (from simple to more complex):

integer –> array has this size and is initialized with 0 bytes:

Code:

>>> bytes(4) b'\x00\x00\x00\x00'

iterable –> integers in the range

Code:

0 <= x < 256

are initial byte contents:

Code:

>>> bytes([1, 2, 3]) b'\x01\x02\x03'

 string and you provide the encoding (and optionally, errors) arguments –>

Code:

bytes()

converts string to bytes using

Code:

str.encode()

:

Code:

>>> bytes('hi', 'UTF-8') b'hi'

object implementing the buffer interface –> initializes the byte object via a read-only object buffer.

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