I'm learning Python, and have run into a bit of a problem. On my OSX install of Python 3.1, this happens in the console:

```
>>> filename = "test"
>>> reader = open(filename, 'r')
>>> writer = open(filename, 'w')
>>> reader.read()
''
>>> writer.write("hello world\n")
12
>>> reader.read()
''

```

And calling `more test` in BASH confirms that there is nothing in test. What's going on?

Thanks.