What's the Difference Between Python String Prefixes 'u', 'r', and 'ur'?

The Nuances of String Prefixes: "u", "r", and "ur"

In the realm of Python strings, confusion often arises regarding the purpose and functionality of the string prefixes "u", "r", and "ur". This article aims to shed light on their distinct roles and the intricacies of raw string literals.

What Raw String Literals Entail

Contrary to common misconceptions, there is no distinct "raw string" type. Instead, "raw string literals" refer to strings prefixed with the letter "r", such as r'...' or r"""...""". These literals differ only in their handling of backslashes ().

In normal string literals, a backslash followed by another character typically triggers an escape sequence, representing special characters like newlines or tabs. Raw string literals, however, interpret the backslash as itself, except when it precedes a closing single or double quote that would otherwise terminate the string.

Differentiating "u", "r", and "ur" Prefixes

The "u" prefix denotes a Unicode string, which is a Unicode object of type unicode. In Python 2.*, u'...' represents a Unicode string, while '...' is a byte string.

The "r" prefix, as discussed earlier, denotes a raw string literal. It preserves backslashes literally, making it useful for regular expressions or when dealing with native Windows file paths. In Python 2.*, both r'...' and r'''...''' produce byte strings.

The "ur" prefix combines the functionality of "u" and "r", resulting in a raw Unicode string literal. Raw Unicode strings are particularly useful when working with file paths that contain Unicode characters.

Converting Between String Types

In Python 2.*, there is a distinction between byte strings and Unicode strings. To convert from a Unicode string to a byte string, one can use the .encode() method. To convert from a byte string to a Unicode string, one can use the .decode() method.

Encodings and String Prefixes

In Python 2.*, the encoding of a string is determined by the codec used to decode the raw byte data (when creating the string) or to encode the Unicode data (when creating the string). The "u" prefix does not affect the encoding of the resulting Unicode string.

In Python 3.*, strings are Unicode-by-default, and the "u" prefix is no longer necessary. Additionally, raw string literals are not needed for regular expressions as backslashes are not treated as escape sequences in raw strings.

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