[Tutor] List problem

[Daniel Yoo]

On Thu, 3 May 2001, Sharriff Aina wrote:

> I tried it ou, heres one variation:
> ### code 
> 
> if allrows[0] == []:


There's a large difference between:

    if allrows[0] == []

and

    if allrows == []

It's only three characters, but to Python, it makes a world of difference.  
Here's an example that might make things clearer:

###
>>> l1 = [()]   # a list whose first element is an empty tuple
>>> l2 = []     # the empty list.
>>> l1[0] == []
0
>>> l2[0] == []
Traceback (innermost last):
  File "<stdin>", line 1, in ?
IndexError: list index out of range
>>> l1 == []
0
>>> l2 == []
1       
###

Let's make a somewhat silly analogy... hmm...

    [()]:  "a honey jar that contains a deflated balloon."
    []  :  "the empty honey jar."

We need to check that allrows isn't an empty honey jar; otherwise, our
hands would get sticky for no good reason.


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