Output from sys.stdout in interactive mode

Question

I tested sys.stdout.write in interactive mode; why do I get the \'extra\' 1 and 2 suffixed to the numbers? If I run the code from a file I get the expected output (1234...)

Answer 1

Python is also echoing the return value of sys.stdout.write() call, which is the number of bytes written:

>>> import sys
>>> written = sys.stdout.write('10')
10>>> written
2

Here the next prompt follows the '10' written without a newline.

Or, as a different way of demoing, writting 0 bytes in a loop prints 0 that many times:

>>> for i in range(3):
...     sys.stdout.write('')
... 
0
0
0