EOFError in Python script

Question

I have the following code fragment:

def database(self):
    databasename=""
    host=""
    user=""
    password=""
    try:
        self.fp=file("detailing.dat","rb")
    except IOError:
        self.fp=file("detailing.dat","wb")
        pickle.dump([databasename,host,user,password],self.fp,-1)
        self.fp.close()
        selffp=file("detailing.dat","rb")
        [databasename,host,user,password]=pickle.load(self.fp)

    return

It has the error:

Traceback (most recent call last):
  File "detailing.py", line 91, in ?
    app=myApp()
  File "detailing.py", line 20, in __init__
    wx.App.__init__(self,redirect,filename,useBestVisual,clearSigInt)
  File "/usr/lib64/python2.4/site-packages/wx-2.6-gtk2-unicode/wx/_core.py", line 7473, in __init__
    self._BootstrapApp()
  File "/usr/lib64/python2.4/site-packages/wx-2.6-gtk2-unicode/wx/_core.py", line 7125, in _BootstrapApp
    return _core_.PyApp__BootstrapApp(*args, **kwargs)
  File "detailing.py", line 33, in OnInit
    self.database()
  File "detailing.py", line 87, in database
    [databasename,host,user,password]=pickle.load(self.fp)
  File "/usr/lib64/python2.4/pickle.py", line 1390, in load
    return Unpickler(file).load()
  File "/usr/lib64/python2.4/pickle.py", line 872, in load
    dispatch[key](self)
  File "/usr/lib64/python2.4/pickle.py", line 894, in load_eof
    raise EOFError
EOFError

What am I doing wrong?

Answer 1

Unless you've got a typo, the issue may be in this line where you assign the file handle to selffp not self.fp:

selffp=file("detailing.dat","rb")

If that is a typo, and your code actually opens the file to self.fp, then you may wish to verify that the file actually has contents (ie: that the previous pickle worked)... the error suggests that the file is empty.

Edit: In the comments to this answer, S. Lott has a nice summary of why the typo generated the error you saw that I'm pasting here for completeness of the answer: "selffp will be the unused opened file, and self.fp (the old closed file) will be used for the load".

Answer 2

Here's the version that I would recommend using:

def database(self):
    databasename=""
    host=""
    user=""
    password=""
    try:
        self.fp=open("detailing.dat","rb")
    except IOError:
        with open("detailing.dat", "wb") as fp:
            pickle.dump([databasename,host,user,password],fp,-1)

        self.fp=open("detailing.dat","rb")
        [databasename,host,user,password]=pickle.load(self.fp)

    return

As has been pointed out, there was a typo on self.fp. But here are a few other things that I notice that can cause problems.

First of all, you shouldn't be using the file constructor directly. You should instead use the built-in open function.

Secondly, you should avoid calling a file's close method outside a finally block. In this case, I've used python 2.6's with block. You can use this in Python 2.5 with the following command:

from __future__ import with_statement

This will prevent the file from being stuck open if an exception is thrown anywhere (as it will close the file when the with block is exited). Although this isn't the cause of your problem, it is an important thing to remember because if one of the file object's methods throws an exception, the file will get held open in sys.traceback indefinitely.

(note that you should probably accept Jarret Hardie's answer though, he caught the bug :-) )