What the heck? open() requires an integer?

[Fausto Arinos de A. Barbuto]

Hi,

    The open() function is returning me a strange error.
    An attempt to create an output file with

            f = open("output.txt","w")

    yields the following error:

    Traceback (most recent call last):
    File "<interactive input>", line 1, in ?
    TypeError: an integer is required

    That happens when I am using either Pythonwin or
    IDLE 0.8, but not in interactive mode. In this latter
    case I can open, write to and close a file OK.

    What's the matter? Thanks in advance!

---Fausto