[Tutor] The Evil eval()

[Timothy M. Brauch]

> > I am getting ready to write a program that will read the contents of a
> file
> > and then manipulate the data.  The file consists of a single list of
lists
> > all on  one line.  Something like:
> >
> > [[1, 2, 3, 4, 5], [2, 4, 6, 8, 10], [3, 6, 9, 12, 15], [4, 8, 12, 16,
20]]
> >
> > If I understand correctly, when I read the file in, I will get a string
> and
> > to make it into a list of lists, I will have to use eval().  But, I also
> > know that is dangerous and if someone knew I used that for this program,
> > they could really mess
>
> If this list of lists is produced by a Python program (as some of the
> answers
> you got until now seem to assume): why not use pickle?

I wish it were only that easy.  I have no idea what language writes the data
files.  I think it is java, though.  All I get are these small data files
and I have to perform mindless computations on it.

> >>> import pickle
> >>> f = open("pickletest.data","w")
> >>> a = [[1, 2, 3, 4, 5], [2, 4, 6, 8, 10], [3, 6, 9, 12, 15], [4, 8, 12,
> 16, 20]]
> >>> pickle.dump(a,f)
> >>> f.close()
> >>> f = open("pickletest.data","r")
> >>> b = pickle.load(f)
> >>> b
> [[1, 2, 3, 4, 5], [2, 4, 6, 8, 10], [3, 6, 9, 12, 15], [4, 8, 12, 16, 20]]
> >>>
>
> Wouldn't this solve your problem?
>
> Gregor

I would use pickle as since learning about it, I have learned to love it.
But, I do not have that convience.

 - Tim

P.S.  My posts are getting through, just a slight four hour delay the last
few days.  Hopefully the mailservers of the world look kindly on this
message.  I am sending it at 13 April 2002 at 12:06am.