the "-u" argument

[Felix]

hi, every one.
i currently have Python 2.1.1 installed on my windows2000 machine,
and i'm really confused by the "-u" argument.

when i use "python -u" to start the interpreter, every time i hit "ENTER"
 the interpreter always produce an error message like below.

>>>
  File "<stdin>", line 1

    ^
SyntaxError: invalid syntax

but i didn't type any statement (thus there can't be any SyntaxError).

does anybody know why this happens?