sorting a list in python without the sorted function

Question

import sys
import pdb

a = [5, 2, 4, 1]

for i in range(len(a)):
    for j in range(len(a) - 1):
        if a[j] > a[j+1]:
            t = a[j]
            a[j] = a[j+1] 
            a[j] = t

print a                   
sys.exit()

I just tried a C program in Python – a normal sort without the sorted function. Why am I not getting the sorted list?

Solution 1

t = a[j]

followed by

a[j] = t

doesn’t seem right. If you meant to swap them, the second one should be:

a[j + 1] = t

But in Python, that’s better written as:

a[j], a[j + 1] = a[j + 1], a[j]

(Of course, in Python, it’s much better written as quicksort.)

Solution 2

Try This -:

for i in range(len(a)):
    for j in range(len(a) - 1):
        if a[j] > a[j+1]:
            a[j+1], a[j] = a[j], a[j+1]

print a

:)

Solution 3

The last line in your for loop should be a[j+1] = t. I think it's just a code mistake. Take care the next time. Also, in Python, when you want to exchange two variables, you should follow what @minitech and @Nilesh G said.

Comments

[johnsyweb]

Why "without the sorted() function"?

[rdodev]

@Johnsyweb I'm guessing it's an assignment. Instructors usually request no built-ins so that students how to do it w/o them.

[rajpython]

@rdodev: yes , as you said. in question sessions and interviews , they expect it without inbuilt function.

[rdodev]

In spite of that this is likely a homework assignment, this is spot-on. Hopefully OP will appreciate and learn from it.

[rdodev]

@minitech had already answer the same thing below, just saying.

[Elizabeth Susan Joseph]

I am new to python programming. could you explain why are you using two for loops here?

[Elizabeth Susan Joseph]

I am new to python programming. could you explain why two for loops are used here? . I know this is a silly question. but I am not able to get the concept.

[Ry-]

@ElizabethSusanJoseph: Don’t worry; it doesn’t really make sense. The inner loop is a bubble sort, and the outer loop runs the bubble sort the absolute maximum number of times it’d take to sort the list using bubble sort (actually, once more than that). You’d usually stop when the list was sorted instead.

[Elizabeth Susan Joseph]

@minitech ok first I will understand what is bubble sort ;). I should have told you that I am new to programming as well. I have completed code academies python exercise. I will learn this concept first.