将项目从python中的另一个列表添加到列表

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?

Answer 1

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']

Answer 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

Answer 3

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

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

Answer 4

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

1. You'll need to work with a indexes:

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

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

Answer 5

我想您想这样做：

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