sort a class object

[docaholic]

how would you sort a class object?

say..you have a card class, and in the card class, you can have the suits and face value of a card.

how would you sort the cards by face values? (smallest to biggest?)

thanks

[vegaseat]

This is very unclear, you got to give us some code!

[docaholic]

ahh...sorry...

ok well, i've got another example, and it deals with a movie class.

how the movie class works is that it stores the name, year and genre of a movie.

ex:
m1 = Movie("Wanted", 2008, Action)
m1.year = 2008
m1.title = "Wanted"
m1.genre = Action

i also have a file with various movies in the text.

my task: read the file and sort all the movies according to year, title, and genre.

here's my code so far:

from movie import *

def findLast(line,char):
    for i in range(len(line)-1, -1, -1):
        if line[i] == char:
            return i
    return -1

m1 = []
file1 = open("movies.txt", "r")
for line in file1:
    tab = line.find("\t")
    newLine = line.find("\n")
    tab2 = findLast(line,"\t")
    title = line[:tab]
    year =line[tab+1:tab2]
    genre = line[tab2+1:newLine]
    m1.append(Movie(title,year,genre))
file1.close()

as you can see, i've taken the entire file and shoved it into a list.

is there a way i can sort the list according to title, year and genre? or am i doing this completely wrong?

[bumsfeld]

This Python code snippet will show you how to do this:
http://www.daniweb.com/code/snippet390.html

[docaholic]

ah... that certainly works....

but...do you have a way to sort it without using the operator module?

i'm not really sure how to use it.

[bvdet]

By adding a __cmp__ method to class Movie, you can sort instance objects in list m1 with list method sort(). Following is an example of a __cmp__ overload in a Vector class that sorts on the x, y and z attributes:

def __cmp__(self, other, epsilon=0.000001):
        x = abs(self.x-other.x)
        if x < epsilon:
            y = abs(self.y-other.y)
            if y < epsilon:
                return cmp(self.z, other.z)
            return cmp(self.y, other.y)
        return cmp(self.x, other.x)

You can also define your own comparison function and pass it to list method sort(). Example using Point objects:

pts = [p1,p2,p3,p4]
>>> pts
[Point(5.000000, 5.000000, 5.000000), Point(7.000000, 10.000000, 6.000000), Point(1.000000, 15.000000, 7.000000), Point(20.000000, 20.000000, 20.000000)]
>>> def comp(a, b):
... 	if a.x == b.x:
... 		if a.y == b.y:
... 			return cmp(a.z, b.z)
... 		return cmp(a.y, b.y)
... 	return cmp(a.x, b.x)
... 
>>> pts.sort(comp)
>>> pts
[Point(1.000000, 15.000000, 7.000000), Point(5.000000, 5.000000, 5.000000), Point(7.000000, 10.000000, 6.000000), Point(20.000000, 20.000000, 20.000000)]
>>>

[docaholic]

ahaha yeah. thanks solsteel. that really helped!