bytes.md

Bytes

The bytes type is an immutable sequence of bytes. The sequence consists of
integers in the range 0 to 255. This data type is used for storing data and data
transmission.

When we open network sockets, work with serial I/O or open binary files, we work
with the bytes type.

Python has a mutable equivalent of the bytes type called bytearray.

The bytes string is a human-readable representation of the bytes type. It
consists of a sequence of ASCII characters between two single, double, or
triple quotes. The bytes string is prefixed with the b character. For printable
ASCII characters, the corresponding character is used. For newline, tab,
carriage return, and \ characters, the escape sequences \n, \t, \r, and
\\ are used. For any other values, hexadecimal escape sequences such as
\xc4 or \xc5 are used.

Each single element of the bytes type is an integer. A slice of bytes returs a slice.

Python bytes example

In the first example, we start working with the bytes type.

s = 'фальконет'
print(s)
print(len(s))

e = s.encode('utf8')
print(e)
print(len(e))

v = bytes('фальконет', 'utf8')
print(v)

w = b'\xd1\x84\xd0\xb0\xd0\xbb\xd1\x8c\xd0\xba\xd0\xbe\xd0\xbd\xd0\xb5\xd1\x82'
print(w)

print('-------------------------')

print(e.decode('utf8'))
print(v.decode('utf8'))
print(w.decode('utf8'))

In the example, we define a Unicode string and transform it to a bytes type.
Then we turn it back to a Unicode string.

s = 'фальконет'
print(s)
print(len(s))

We define a Unicode string and print it and its size in characters.

e = s.encode('utf8')
print(e)

We encode the string into a bytes type.

print(len(e))

We print the number of bytes in the bytes string.

v = bytes('фальконет', 'utf8')

We can get the bytes type using the built-in bytes function.

w = b'\xd1\x84\xd0\xb0\xd0\xbb\xd1\x8c\xd0\xba\xd0\xbe\xd0\xbd\xd0\xb5\xd1\x82'
print(w)

We define a bytes string.

print(e.decode('utf8'))
print(v.decode('utf8'))
print(w.decode('utf8'))

Here we decode the three bytes into Unicode strings.

$ ./main.py
фальконет
9
b'\xd1\x84\xd0\xb0\xd0\xbb\xd1\x8c\xd0\xba\xd0\xbe\xd0\xbd\xd0\xb5\xd1\x82'
18
b'\xd1\x84\xd0\xb0\xd0\xbb\xd1\x8c\xd0\xba\xd0\xbe\xd0\xbd\xd0\xb5\xd1\x82'
b'\xd1\x84\xd0\xb0\xd0\xbb\xd1\x8c\xd0\xba\xd0\xbe\xd0\xbd\xd0\xb5\xd1\x82'
-------------------------
фальконет
фальконет
фальконет

Python transmitting bytes

The data on the network is transmitted in the bytes type.

import requests

url = 'http://webcode.me/small.txt'

req = requests.get(url)

print(req.content)
print(req.content.decode('utf8'))

We generate a GET request to a small text resource.

print(req.content)

Printing the request content, we get a bytes string.

print(req.content.decode('utf8'))

We turn the bytes string into a Unicode string with decode.

$ ./main.py 
b'small text page\n'
small text page

Python bytes read binary

When we open a file in binary mode, we retrieve the data in bytes.

The data.txt file:

Dnes bol krásny deň. 
Dážď bubnoval na okenice.
We have this text file.

with open('data.txt', 'rb') as f:

    lines = f.readlines()

    print(lines)

    for line in lines:
        print(line.decode().rstrip())

We read a text file in binary mode.

with open('data.txt', 'rb') as f:

We open the text file in rb mode.

lines = f.readlines()

We get a list of bytes strings.

for line in lines:
    print(line.decode().rstrip())

We go over the list and print the decoded lines.

$ ./main.py 
[b'Dnes bol kr\xc3\xa1sny de\xc5\x88. \r\n', b'D\xc3\xa1\xc5\xbe\xc4\x8f bubnoval na okenice.']
Dnes bol krásny deň.
Dážď bubnoval na okenice.

Python bytes representations

In the following example, we represent bytes in different numerical systems.

from more_itertools import sliced

s = 'château'
print(s)

v = s.encode('utf8')
print(v)

h = v.hex()
print(h)

d = list(sliced(h, 2))
print(d)

i = int(h, 16)
b = bin(i)

print(i)
print(b)

print(bytes.fromhex(f'{int(b, 2):x}').decode('utf8'))

We turn a French word château into a bytes type. The type is then displayed
in hexadecimal, integer, and binary values.

s = 'château'
print(s)

We define a Unicode string.

v = s.encode('utf8')
print(v)

The string is encoded into a bytes string.

h = v.hex()
print(h)

We transform the bytes string into a hex string.

d = list(sliced(h, 2))
print(d)

We turn the hex string into a list of hexadecimal values.

i = int(h, 16)

We transform the hex string into an integer.

b = bin(i)

The decimal integer is transformed into binary.

print(bytes.fromhex(f'{int(b, 2):x}').decode('utf8'))

We turn the binary back into the Unicode string.

$ ./main.py
château
b'ch\xc3\xa2teau'
6368c3a274656175
['63', '68', 'c3', 'a2', '74', '65', '61', '75']
7163190309837693301
0b110001101101000110000111010001001110100011001010110000101110101
château