[Tutor] Building Starships -- object of type 'int' has no len()

[Joseph Lee]

Hi,
My thoughts are in the message:



 ----- Original Message -----
From: Terry--gmail <terry.kemmerer at gmail.com
To: Python_Tutor -- Mailing List <tutor at python.org
Date sent: Fri, 15 Aug 2014 11:46:49 -0600
Subject: [Tutor] Building Starships -- object of type 'int' has 
no len()

Python 3.3

This has something to do with the nature of FOR statements and IF
statements, and I am sure it must be a simple mistake...but I 
seem to be
stumped.

I am writing a starship encounter program as my first real python
program....where the user gets a random amount of credits to 
design his
own ship and the computer also gets a random number of credits to 
spend
and designs it's own ship, and then they go into combat against 
each other.

This is part of the design phase for the user.  The user has 
picked one
category of the catalog, such as:

Hulls, Drives, Shields, Weapons, Personnel, etc

catalog and catalog2 are lists of lists:  [[],[],[]]

OK.  So, my program has scanned the master catalog for a 
particular
chosen category and has built catalog2 containing all the parts 
of that
one category and their associated differences (rows), and now I 
want to
print it out as a menu for the user to pick what part to add of 
this
particular category to his ship.

But first, so that I can pretty print the menu items and their
associated capabilities to the screen in nice uniform columns, I 
need to
know the maximum size of what is going to be printed in each 
column on
the screen in advance, so I do the below learning scan through 
catagory2
and I build the simple list 'lens' to contain the max size of 
each column.

As I run the program, this works perfectly for every NEW category 
the
user picks, and the rows of associated data are printed just like 
I
want.......*UNTIL the user chooses to buy a second part from a 
category
he has already visited*, and at that point things error out.  
Below is
the problem code and the error:


lens = []

# pre-format the list called lens for maximum number of columns
contained in catalog2

lens = [0] * len(catalog2[0])

# map the largest sizes of each column into list 'lens'

col, line_number = 0, 0

for line_number in range(len(catalog2)):

for col in range(len(catalog2[line_number])):

*if lens[col] < len(catalog2[line_number][col]):*

lens[col] = len(catalog2[line_number][col])


Traceback (most recent call last):
   File "encounter.py", line 379, in <module
     myship = designShip(credits, myship)
   File "encounter.py", line 354, in designShip
     hull, myship, credits, section = nicePrint(hull, credits, 
myship,
catalog, section)
   File "encounter.py", line 199, in nicePrint
if lens[col] < len(catalog2[line_number][col]):


JL: Hmmm, what is the type of the item stored at that location? 
Based on the surrounding code, what you're telling me is that you 
wish to know the length of that particular line/column location, 
and if it is not a sequence (list, string, etc.), Python will 
throw that error.  So it appears to me that you're attempting to 
use something that the type of the item doesn't support.


TypeError: *object of type 'int' has no len()*

I don't get it.  This code does the same job, again and again
successfully as I proceed to pick new categories.  Why would it 
care if I
want to go over the same ground more than once??? It seems to me 
that
the FOR STATEMENT automatically zeros the counters 'col' and
line_number' when it starts counting, but why would it suddenly 
choke
because of going over old territory???

In trying to debug i have checked catalog2 and it's data is 
present and
intact.  I added  the line 'col, line_number = 0, 0' in the 
sequence of
events although I don't see why it would be needed, and evidently 
it
isn't needed because the problem persists.  What's left to check?

I really want to buy more guns and bombs and armor! But the 
program
seems to be on the side of gun control!!!
:)
Thanks for your thoughts and suggestions!





Cheers,
Joseph