Python bytes() built-in function
From the Python 3 documentation
Return a new “bytes” object which is an immutable sequence of integers in the range [...]. bytes is an immutable version of bytearray – it has the same non-mutating methods and the same indexing and slicing behavior.
Introduction
In Python, the bytes type is an immutable sequence of single bytes. It represents a sequence of integers in the range of 0 to 255, which can be used to represent binary data such as images, audio, or other types of files.
You can create a bytes object in several ways. One way is to use the bytes() constructor and pass it a string, a bytearray object, or a bytes object. For example:
>>> data = "Hello, World!"
>>> bytes_obj = bytes(data, "utf-8")
>>> print(bytes_obj)
# b'Hello, World!'
Another way is to use a literal notation prefixing the string with b or B:
data = b"Hello, World!"
print(data)
# b'Hello, World!'