[xenor]

def qsort1(lst):
	if len(lst) <= 1:
		return lst
	pivot = lst.pop(0)
	greater_eq = qsort1([i for i in lst if i >= pivot])
	lesser = qsort1([i for i in lst if i < pivot])
	return lesser + [pivot] + greater_eq
 

Can someone please explain to me how this line is working?

qsort1([i for i in lst if i >= pivot])

[Dogstopper]

Quote

Can someone please explain to me how this line is working?

qsort1([i for i in lst if i >= pivot])

This line sets a variable i to every index(also i (the second one)) only if i >= pivot. Then with this list of true values (the ones that meet the criteria of >= pivot) the qsort() function is called again with this new list of values as it's parameters; this is called recursion.

[xenor]

 i for

I can't understand the meaning of this?

 [] 

Lists?

This post has been edited by xenor: 08 November 2009 - 12:33 PM

[Tshiknn]

xenor, on 8 Nov, 2009 - 11:33 AM, said:

 i for

I can't understand the meaning of this?

 [] 

Lists?

What you're looking at is a Python feature called a listcomp, or list comprehension. For example:

example1 = []
example2 = []

# these do the same thing.
example1 = [i for i in xrange(10)]
for i in xrange(10):
	example2.append(i)

Your example is a bit more complex. Here we apply a filter. Simply explained, with a filter a listcomp will check the if statement first and then if it's true add the iterator value. For example:

example1 = [i for i in xrange(10) if i % 2 == 0]

Now i is populated with [0, 2, 4, 6, 8]. Now that you understand listcomps (hopefully), your example simply calls qsort1, giving it a list populated with values more than or equal to the pivot point.

[xenor]

Thanks a lot i understand the part that you explained to me.

 return lesser + [pivot] + greater_eq

What is the meaning of this?
That will return ......

[xenor]

The "myth" has been solved

 return lesser + [pivot] + greater_eq

This part is used to connect lesser + pivot + greater_eq element that are derived from:

  
greater_eq = qsort1([i for i in lst if i >= pivot])
lesser = qsort1([i for i in lst if i < pivot])

[Dogstopper]

There you go! Sorry for not getting back to you, i was away.

[xenor]

Tnx to anyone who helped me. See ya.