What is "\00" in Python?

Question

What does "\00" mean in Python? To learn more about this, I tried following:

• When I assign d="\00" and call print d, nothing displays on the screen.
• I also tried assigning d to a string with extra spacing between and at the end and then called d.replace("\00", ""), but no result was evident.

What does d.replace("\00","") do? Will it merely look for this particular string "\00" and replace it with an empty string?

Solution 1

In Python 2, when a number starts with a leading zero, it means it's in octal (base 8). In Python 3 octal literals start with 0o instead. 00 specifically is 0.

The leading \ in \00 is a way of specifying a byte value, a number between 0-255. It's normally used to represent a character that isn't on your keyboard, or otherwise can't be easily represented in a string. Some special characters also have non-numeric "escape codes", like \n for a newline.

The zero byte is also known as the nul byte or null byte. It doesn't display anything when printed -- it's null.

See http://www.ascii.cl/ for ASCII character codes.

Yes, replace will still work with it, it just has no meaning as a display character.

It's sometimes used for other purposes, see http://en.wikipedia.org/wiki/Null_character.

Solution 2

The backslash followed by a number is used to represent the character with that octal value. So your \00 represents ASCII NUL.

Comments

[Pankaj Upadhyay]

So what will replace do ?. Will it merely treat "\00" as a plain string; to be replace by "".

[agf]

Yes, it will replace the zero byte with whatever string you specify, just as if you replaced 'a' or ' ' (space) or '\t' (tab).

[John Machin]

No such thing as "ASCII NULL". It's NUL. NULL is the SQL equivalent of Python's None.

[Duncan]

@agf note that '\0' is actually base 8 not base 10. It doesn't make any difference for nulls, but as soon as you start using it for any character over 7 it will make a big difference.

[agf]

@Duncan is right -- \0 is octal, while \x00 is hexadecimal, and both are null.

[mins]

@JohnMachin, or NULL is to NUL what LINE FEED is to LF (meaning vs abbreviation)