Function programming in Python

Question

I'm trying to define a new function called new_f, just for practice:
The purpose of function is:

x = ['1', '2', '3', '4']
y = new_f(x)
print(y)

And that should give:

['4', '3', '2', '1']

So it's a reverse of x.
I tried something like this:

def new_f(x):
    y = len(x)
    for z in range(y-1,-1,-1):
        r = print([x[z]])
    return r

But that gives:

['4']
['3']
['2']
['1']

Ok, that's not what I want, so maybe:

---------
for z in range(y-1,-1,-1):
        r = [x[z]]
return r

And I get:

['1']

So he goes through all z and gives me the last one.
How can I resolve this problem?
Thanks in advance.

list[::-1] means you've masked the built-in function list() with a reference to an object of type list. — TigerhawkT3
– TigerhawkT3, Commented Apr 29, 2015 at 23:04

Kasravnd · Accepted Answer · 2015-04-29 23:14:16Z

4

You can initial r as an empty list and append the elements to it and at last return the r

def new_f(x):
    y = len(x)
    r=[]
    for z in range(y-1,-1,-1):
        r.append(x[z])
    return r

But there are some elegant and more pythonic ways for reversing a list like reverse indexing :

the_list[::-1]

or built-in reversed function :

reversed(the_list)

edited Apr 29, 2015 at 23:14

answered Apr 29, 2015 at 23:01

Kasravnd

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1 Comment

VlS Over a year ago

Thank you @Kasra that's exactly how I wanted.

hebrewduck · Accepted Answer · 2015-04-29 23:02:43Z

3

You can use Python's slicing operator to reverse a list.

def new_f(x):
        return x[::-1]

answered Apr 29, 2015 at 23:02

hebrewduck

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Comments

Alireza Bashiri · Accepted Answer · 2015-08-06 18:09:03Z

1

Maybe you'd find them useful:

def reverse_list(x):
    return x.reverse()

def reverse_list(x):
    return x[::-1]

def reverse_list(x):
    yield from reversed[x]

edited Aug 6, 2015 at 18:09

answered Apr 29, 2015 at 23:06

Alireza Bashiri

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2 Comments

Shashank Over a year ago

Hey, I think instead of yield from reversed(x) you can just do return reversed(x). I mean it's the same exact thing, just shorter, and faster.

Alireza Bashiri Over a year ago

oh, yes. It's returns list_reverseiterator empty instance but yield returns a generator empty instance, that's the only difference :D

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