Unexpected format string behavior

Question

I just ran into what seemed to me to be bizarre string formatting behavior in python. It turned out to be caused by carriage return characters ('\r') I didn't know were there. Here's an example:

>>> text = 'hello\r'
>>> '(SUBJECT "%s")' % (text)
'(SUBJECT "hello\r")'
>>> print '(SUBJECT "%s")' % (text)
")UBJECT "hello

I tried the same thing in C (on a couple machines) as a sanity check.

#include <stdio.h>

int main()
{
    char *text = "hello\r";
    printf("(SUBJECT \"%s\")\n", text);
    return 0;
}

Output:

% ./a.out
")UBJECT "hello

Is this desired behavior? If so, can someone explain what is going on?

Answer 1

It (\r) is a carridge return without a linefeed so the cursor moves back to the start of the current line without moving onto a new line and therefore overwriting what is already displayed.

The behaviour depends on your console and whether it interprets CR and LF as individual operations.