Transform a list

问题

The input:

 lst=[ '  22774080.570 7                   1762178.392 7   1346501.808 8  22774088.434 8\n',
     '  20194290.688 8                  -2867460.044 8  -2213132.457 9  20194298.629 9\n']

The desired output:

['22774080.570 7','none','1762178.392 7','1346501.808 8','22774088.434 8'],
['20194290.688 8','none','-2867460.044 8', .... ]

回答1:

I've made a few assumptions here, and this is probably not the most elegant solution, but given that your matching None based on the length of space, this will work

[[(None if a.strip() == 'None' else a.strip()) 
    for a in l.replace('                  ', '  None  ').split('  ')  if a != ''
    ] for l in lst]

this is currently implemented as a list comprehension, but could easily be spread over multiple lines for readability as such

new_list = []
for l in lst:
    sub_list = []
    for a in l.replace('                  ', '  None  ').split('  '):
        if a != '':
            item = a.strip()
            sub_list.append(None if item == 'None' else item)
    new_list.append(sub_list)

either method yields the same result:

[
 [
  '22774080.570 7', None, '1762178.392 7', '1346501.808 8', '22774088.434 8'
 ], 
 [
  '20194290.688 8', None, '-2867460.044 8', '-2213132.457 9', '20194298.629 9'
 ]
]

Bear in mind that any changes to the width of spaces used to define 'None' will impact the function of this implementation.

回答2:

I will not answer your question right away because it is not how stackoverflow works but I will give you some hints.

HINTS

• First, you can iterate over each line of your first list lst using a for loop.

• Then, you need to split every numbers of this line, luckily for you, it took always 16 characters. In python, there is severals way to do so. A good training for you will be to use the range function in a for loop. Then use slicing in python strings.

• Now, it could remains some extra spaces in the beginning of every numbers. A good way to remove them is to use the strip() function.

• Last thing you need to do is to append every clean strings to a new list (e.g. result)

END

I will edit my answer with a working function as soon as you edit yours with a proper try. Good luck!

EDIT

Since my namesake @Max Chesterfield already gave an answer, I'll give mine. Instead of using lists of list, you can use a generator to match exactly the desired output

def extract_line():
    for line in lst:
        result = []
        for i in range(0, len(line) - 1, 16):
            numbers = line[i:i + 16].strip()
            result.append(numbers if numbers else None)
        yield result

for result in extract_line():
    print(result)

Will output:

['22774080.570 7', None, '1762178.392 7', '1346501.808 8', '22774088.434 8']
['20194290.688 8', None, '-2867460.044 8', '-2213132.457 9', '20194298.629 9']

来源：https://stackoverflow.com/questions/40507313/transform-a-list