Second python program: classes, sorting

[Bruno Desthuilliers]

WP a écrit :
> Hello, here are some new things I've problems with. I've made a program 
> that opens and reads a text file. Each line in the file contains a name 
> and a score. I'm assuming the file has the correct format. Each 
> name-score pair is used to instantiate a class Score I've written. This 
> works fine, but here's my problem: After reading the file I have list of 
> Score objects. Now I want to sort them in descending order. But no 
> matter how I write my __cmp__ the order remains unchanged. 

You fixed this, so I'll just comment on the rest of the code...

(snip)


> Complete program:
> class Score:

Unless you have a compelling reason (mostly: compat with ages old Python 
versions), better to use new-style classes:

class Score(object):

>     def __init__(self, name_, score_):
>         self.name = name_
>         self.score = score_

cf Eric Brunel's comments here about the trailing underscores.

>     def __str__(self):
>         return "Name = %s, score = %d" % (self.name, self.score)
> 
(snip)

>     name  = ""
>     score = 0

Do you have any reason to have these as class attributes too ?


> # End class Score
> 
> filename = "../foo.txt";
> 
> try:
>     infile = open(filename, "r")
> except IOError, (errno, strerror):
>     print "IOError caught when attempting to open file %s. errno = %d, 
> strerror = %s" % (filename, errno, strerror)
>     exit(1)

cf Eric Brunel's comment wrt/ why this try/except clause is worse than 
useless here.

> lines = infile.readlines()

File objects are their own iterators. You don't need to read the whole 
file in memory.

> infile.close()

> lines = [l.strip() for l in lines] # Strip away trailing newlines.
> 
> scores = []
> 
> for a_line in lines:

>     splitstuff = a_line.split()
> 
>     scores.append(Score(splitstuff[0], int(splitstuff[1])))


scores = []
mk_score = lambda name, score : Score(name, int(score))

infile = open(filename)
for line in infile:
     line = line.strip()
     if not line:
         continue
     scores.append(mk_score(*line.split()))

infile.close()


As a side note : I understand that this is a learning exercice,  but in 
real life, if that's all there is to your Score class, it's not really 
useful - I'd personnally use a much simpler representation, like a list 
of score / name pairs (which is easy to sort, reverse, update, turn into 
a name=>scores or scores=>names dict, etc).

My 2 cents.