Why is '\x' invalid in Python?

python string ascii backslash control-characters
PaulMcG picture PaulMcG · Apr 24, 2010 · Viewed 31.3k times · Source

I was experimenting with '\' characters, using '\a\b\c...' just to enumerate for myself which characters Python interprets as control characters, and to what. Here's what I found:

\a - BELL
\b - BACKSPACE
\f - FORMFEED
\n - LINEFEED
\r - RETURN
\t - TAB
\v - VERTICAL TAB

Most of the other characters I tried, '\g', '\s', etc. just evaluate to the 2-character string of a backslash and the given character. I understand this is intentional, and makes sense to me.

But '\x' is a problem. When my script reaches this source line:

val = "\x"

I get:

ValueError: invalid \x escape

What is so special about '\x'? Why is it treated differently from the other non-escaped characters?

Answer

Mark Byers picture Mark Byers · Apr 24, 2010

There is a table listing all the escape codes and their meanings in the documentation.

Escape Sequence    Meaning                        Notes
\xhh               Character with hex value hh    (4,5)

Notes:

4. Unlike in Standard C, exactly two hex digits are required.
5. In a string literal, hexadecimal and octal escapes denote the byte with the given value; it is not necessary that the byte encodes a character in the source character set. In a Unicode literal, these escapes denote a Unicode character with the given value.

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