CODEWITHSUNDEEP
pythonlistreverse
Maggie Mi
Maggie Mi

Reputation: 89

Python deep reverse in a list

I have a nested list, and I need to reverse every element in the list. But I dont know whether the list is a list of list of list or not. So example is:

p = [1, [2, 3, [4, [5, 6]]]]
print deep_reverse(p)
#>>> [[[[6, 5], 4], 3, 2], 1]

q =  [1, [2,3], 4, [5,6]]
print deep_reverse(q)
#>>> [ [6,5], 4, [3, 2], 1]

What I have so far is:

def is_list(p):
    return isinstance(p, list)

def deep_reverse(a):
    a.reverse()
    for i in a:
        if is_list(i):
            i.reverse()
            print a

It works well for the second test, the q one, but doest work for the first test. I am not sure do I need use a recursion to loop the whole thing? How can I modify my code? Thanks.

Upvotes: 2

Views: 8801

Answers (10)

Just A Random Guy
Just A Random Guy

Reputation: 1

I am going old school on this problem's butt:

def deepReverse(L):
    """Input a list tot output a reversed form of it"""
    if not L:
        return []
    elif isinstance(L[-1], list):
        return [deepReverse(L[-1])] + deepReverse(L[0:-1])
        
    else:
        return [L[-1]] + deepReverse(L[0:-1])

Upvotes: 0

Bhargava Mourya
Bhargava Mourya

Reputation: 13

Here is my solution

def is_list(p):
    return isinstance(p, list)
   
def deep_reverse(p):

 if p==[]:
    return p

 if not is_list(p[0]):
    return deep_reverse(p[1:])+[p[0]]
 
 else:
    return deep_reverse(p[1:])+[deep_reverse(p[0])]

Upvotes: 1

Manu
Manu

Reputation: 112

most elegant:

def deep_reverse(L):
    """ assumes L is a list of lists whose elements are ints
    Mutates L such that it reverses its elements and also 
    reverses the order of the int elements in every element of L. 
    It does not return anything.
    """
    # Your code here
    for i in L:
        try:
            deep_reverse(i)
        except:
            pass
    L.reverse()

Upvotes: 0

o0omycomputero0o
o0omycomputero0o

Reputation: 3534

def is_list(p):
    return isinstance(p, list)

def deep_reverse(p):

 if p==[]:
    return p

 if not is_list(p):
    return p
 else:
    return deep_reverse(p[1:])+[deep_reverse(p[0])]

test ok.

Upvotes: 0

mazlor
mazlor

Reputation: 1895

here is a suggestion : 

def deep_reverse(lst):
    if isinstance(lst ,list):
        if sum(1 for x in lst if isinstance(x, list)) == 0:
                        lst = lst[::-1]
                        return lst
        else :
            lst = lst[::-1]
            lst = [deep_reverse(item) for item in lst]     
            return lst
    else:
         return lst

Upvotes: 0

Jeff Mercado
Jeff Mercado

Reputation: 134811

def deep_reverse(lst):
    try:
        if len(lst) > 1:
            return list(deep_reverse(item) for item in reversed(lst))
        return lst
    except TypeError:
        return lst

Upvotes: 4

jamylak
jamylak

Reputation: 133504

>>> def deep_reverse(L):
        for item in reversed(L):
            if isinstance(item,list):
                yield list(deep_reverse(item))
            else:
                yield item


>>> p = [1, [2, 3, [4, [5, 6]]]]
>>> q =  [1, [2,3], 4, [5,6]]
>>> list(deep_reverse(p))
[[[[6, 5], 4], 3, 2], 1]
>>> list(deep_reverse(q))
[[6, 5], 4, [3, 2], 1]

Upvotes: 1

whi
whi

Reputation: 2750

def deep_reverse(ls):  
    for i in ls:  
        if type(i)==list:deep_reverse(i)  
    ls.reverse()

Upvotes: 0

inspectorG4dget
inspectorG4dget

Reputation: 113905

def deep_reverse(L):
    if L == []:
        return L
    elif type(L) == int:
        return L
    else:
        return deep_reverse(L[1:]) + [deep_reverse(L[0])]

>>> print deep_reverse(p)
[[[[6, 5], 4], 3, 2], 1]

>>> print deep_reverse(q)
[[6, 5], 4, [3, 2], 1]

Hope this helps

Upvotes: 1

ielashi
ielashi

Reputation: 245

The reason your code doesn't work is because if i is a list of lists, you don't deep_reverse the lists within i.

You only need to change one line of your code to the following:

def is_list(p):
    return isinstance(p, list)

def deep_reverse(a):
    a.reverse()
    for i in a:
        if is_list(i):
            deep_reverse(i)  # <=== This is what changed
            print a

Upvotes: 4

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