Comparison problem

Tom Anderson twic at urchin.earth.li
Sat Nov 26 21:32:22 CET 2005


Chris, as well as addressing what i think is causing your problem, i'm 
going to point out some bits of your code that i think could be polished a 
little. It's intended in a spirit of constructive criticism, so i hope you 
don't mind!

On Sat, 26 Nov 2005, Chris wrote:

>    if item[0:1]=="-":

item[0:1] seems a rather baroque way of writing item[0]! I'd actually 
suggest writing this line like this:

if item.startswith("-:):

As i feel it's more readable.

>     item=item[ :-7]
>     item=item[1:]

You could just write:

item = item[1:7]

For those two lines.

>     infile=open("inventory","r")

The "r" isn't necessary - reading is the default mode for files. You could 
argue that this documents your intentions towards the file, i suppose, but 
the traditional python idiom would leave it out.

>     while infile:
>      dummy=infile.readline()

The pythonic idiom for this is:

for dummy in infile:

Although i'd strongly suggest you change 'dummy' to a more descriptive 
variable name; i use 'line' myself.

Now, this is also the line that i think is at the root of your trouble: 
readline returns lines with the line-terminator ('\n' or whatever it is on 
your system) still on them. That gets you into trouble later - see below.

When i'm iterating over lines in a file, the first thing i do with the 
line is chomp off any trailing newline; the line after the for loop is 
typically:

line = line.rstrip("\n")

>      if dummy=='':break

You don't by any chance mean 'continue' here, do you?

>      print item
>      print ", "+dummy
>      if (dummy == item): <This comparison isn't working>

This is where it all falls down - i suspect that what's happening here is 
that dummy has a trailing newline, and item doesn't, so although they look 
very similar, they're not the same string, so the comparison comes out 
false. Try throwing in that rstrip at the head of the loop and see if it 
fixes it.

HTH.

tom

-- 
Gotta treat 'em mean to make 'em scream.



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