What Does the 'b' Prefix Mean in Python Strings?

The Effects of the 'b' Character in Python

In Python, the 'b' character can be prefixed to a string literal to create a bytes object. This serves to make a distinction between string and byte data types, as Python 3.x clearly differentiates between the two:

• str: A sequence of Unicode characters.
• bytes: A sequence of bytes, addressing the smallest integer on the computer.

Usage of 'b' Prefix

Utilize 'str' to represent text, and 'bytes' when representing binary data. For instance:

# Represent text
print('Hello world')

# Represent binary data (NaN in big-endian)
NaN = struct.unpack('>d', b'\xff\xf8\x00\x00\x00\x00\x00\x00')[0]

Mixability of Types

Avoid mingling str and bytes types directly. For example:

# Error in Python 3.x
b'\xEF\xBB\xBF' + 'Text with a UTF-8 BOM'

Behavior in Python 2.x

In Python 2.x versions, the 'b' prefix has no effect but serves as an indicator not to convert the string to Unicode in Python 3.x. This is useful for distinguishing binary strings from text strings during migration.

Other String Literals

Besides 'b', Python also supports:

• r: Raw strings (e.g., 't' retains its literal meaning)
• Triple quotes: Multi-line strings
• f: Formatted strings (introduced in Python 3.6)

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