8.7 Binary Type Conversion

bytes, bytearray, and memoryview themselves are covered in 5.7 Binary Data Types — this section focuses on the conversion rules for constructing each from other types, essential whenever Python touches files, sockets, or non-text data.

bytes()

Converts a list of integers (0–255), or a str with an explicit encoding, into an immutable bytes object.

>>> bytes([65, 66, 67])
b'ABC'
>>> bytes("hi", "utf-8")
b'hi'

bytearray()

Same conversion rules as bytes(), but produces a mutable result that can be modified in place afterward.

>>> bytearray("hi", "utf-8")
bytearray(b'hi')

memoryview()

Wraps an existing bytes/bytearray object as a zero-copy view — converting it back to a list of integers shows the underlying byte values without duplicating the buffer.

>>> list(memoryview(b"hi"))
[104, 105]

Quick Interview Answer

“bytes() builds an immutable byte sequence either from a list of integers in the 0–255 range, or from a str given an explicit encoding — Python never guesses an encoding, it must be stated. bytearray() follows the same construction rules but produces a mutable result. memoryview() is different in kind: it doesn’t copy data at all, just wraps an existing bytes/bytearray buffer, which matters for processing large binary data without duplicating it in memory.”

Common Mistakes

• Calling bytes("hi") without an encoding argument — unlike some conversions, str to bytes requires an explicit encoding; Python won’t assume one.
• Expecting memoryview() to copy data like the other conversions do — it’s a zero-copy view onto the original buffer, not a new independent object.