What is the Implication of Preceding \'r\' Before String Literals in Python?

What's the Significance of Preceding String Literals with "r"?

In Python, when a string literal is preceded by the character "r" (standing for "raw"), it designates that the string will be treated as a raw string. This implies that escape codes within the string will be disregarded.

For instance, in regular expression builds, the "r" prefix ensures that backslash characters are considered part of the string rather than escape characters. Below is an example:

<code class="python">regex = re.compile(
    r'^[A-Z]'
    r'[A-Z0-9-]'
    r'[A-Z]$', re.IGNORECASE
)</code>

The "r" prefix in this example prevents the escape code "n" (which denotes a newline) from being interpreted as a line break character. Instead, it is treated as the characters "n".

Distinction from Regular Strings

Regular strings and raw strings differ in their handling of escape sequences. While regular strings process escape characters like "n" as special characters, raw strings leave them as-is. This allows for more flexibility when working with strings containing characters that would otherwise be interpreted as escape codes.

Official Explanation

According to the Python documentation, when a string literal has an "r" or "R" prefix, "a character following a backslash is included in the string without change, and all backslashes are left in the string." This further clarifies that raw strings cannot have odd numbers of backslashes as the last character, which would lead to a syntax error.

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