Adding an item to a list from another list in python

Question

I need to be able to add an item into list a from list b. The item from list b is to be added as soon as ' ' which is a double space is identified.

Therefore if the first item in the list is not a double space, then the loop goes on to check the next item in the list, if its also not a double space, it carries on until if finds the double space and then it replaces the first available double space with the item from list b. This should be looped so that if I run the function again, an item in list b is popped and added to the next available double space in list a.

a = ['a','c','e','j','h','  ','  ','  ','  ']
b = ['b','d','f','i','g']

x = 4
for item in a:
    if item == a[4]:
        break
if a[x] != '  ':
    a[x+1] = b.pop(-2)

else:
    a[x] = a[x+1]

print("list a: ",a)
print("List b: ",b)

Output:

list a:  ['a', 'c', 'e', 'j', 'h', 'i', '  ', '  ', '  ']
List b:  ['b', 'd', 'f', 'g']

That works, but I have a feeling my code doesn't work on all inputs. Does it? If it doesn't, what's wrong?

So it works or not? x=4 is i and i really moved from b to the first available place in list a — Ofir Baruch
– Ofir Baruch, Commented Mar 9, 2012 at 20:21
@OfirBaruch; i was kinda cheating to get it to work but i think x should be = 0 to enable it to start checking from the first item in list a. but i could not get it to work with x=0. — Lycon
– Lycon, Commented Mar 9, 2012 at 20:25
so am i understanding this correctly? you need to replace each double space in a with an element from b, in order? — aeroNotAuto
– aeroNotAuto, Commented Mar 9, 2012 at 20:29

Andrew Clark · Accepted Answer · 2012-03-09 20:38:17Z

2

I think this is what you are looking for:

def move_item(a, b):
    a[a.index('  ')] = b.pop()

>>> a = ['a','c','e','j','h','  ','  ','  ','  ']
>>> b = ['b','d','f','i','g']
>>> move_item(a, b)
>>> print('list a: ', a, '\nlist b: ', b)
list a:  ['a', 'c', 'e', 'j', 'h', 'g', '  ', '  ', '  ']
list b:  ['b', 'd', 'f', 'i']
>>> move_item(a, b)
>>> print('list a: ', a, '\nlist b: ', b)
list a:  ['a', 'c', 'e', 'j', 'h', 'g', 'i', '  ', '  ']
list b:  ['b', 'd', 'f']

edited Mar 9, 2012 at 20:38

answered Mar 9, 2012 at 20:30

Andrew Clark

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2 Comments

Lycon Over a year ago

but i only need one item at a time from list b. how could i edit your code to achieve this.

Andrew Clark Over a year ago

@Lycon - I've edited my answer to make it easier to do this one item at a time.

cjm · Accepted Answer · 2012-03-09 20:32:08Z

2

This:

a = [b.pop() if item == '  ' else item for item in a]

gets you:

['a', 'c', 'e', 'j', 'h', 'g', 'i', 'f', 'd']

Take a look at Python list comprehensions

answered Mar 9, 2012 at 20:32

cjm

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Comments

Reinstate Monica · Accepted Answer · 2012-03-09 20:28:38Z

0

You didn't ask a question, but here are some hints:

list.index, list.pop, a[index_of_doublespace] = popped_value_from_b

answered Mar 9, 2012 at 20:28

Reinstate Monica

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Rik Poggi · Accepted Answer · 2012-03-09 20:32:00Z

0

Since this homework, I'm just going to give you some hints:

You'll need to work with a indexes:

for i in range(len(a)):
    if a[i] == ??? :
        a[i] = ??

Why are you popping the -2th element? Check out what pop does.

answered Mar 9, 2012 at 20:32

Rik Poggi

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Density 21.5 · Accepted Answer · 2012-03-09 20:35:37Z

0

I guess you want to do this:

[x.split(' ')[0] or b.pop() for x in a]

answered Mar 9, 2012 at 20:35

Density 21.5

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