Python嵌套循环 - 接下来的N行

Question

我是Python的新手,并试图做一个嵌套循环.我有一个非常大的文件(110万行),我想用它来创建一个文件,每行包含接下来的N行,例如接下来的3行:

1    2
1    3
1    4
2    3
2    4
2    5

现在我只是试图让循环使用rownumbers而不是字符串,因为它更容易可视化.我想出了这个代码,但它的表现并不像我想要的那样:

with open('C:/working_file.txt', mode='r', encoding = 'utf8') as f: 
for i, line in enumerate(f):
     line_a = i
     lower_bound = i + 1
     upper_bound = i + 4
     with open('C:/working_file.txt', mode='r', encoding = 'utf8') as g:
        for j, line in enumerate(g):
            while j >= lower_bound and j <= upper_bound:
                line_b = j
                j = j+1
                print(line_a, line_b)

它不是我想要的输出,而是给我这个:

990     991
990     992
990     993
990     994
990     992
990     993
990     994
990     993
990     994
990     994

正如您所看到的,内循环对外循环中的每一行迭代多次.看起来外循环中每行只应该有一次迭代.我错过了什么？

编辑:我的问题在下面得到解答,这是我最终使用的确切代码:

from collections import deque
from itertools import cycle
log = open('C:/example.txt', mode='w', encoding = 'utf8') 
try:
    xrange 
except NameError: # python3
    xrange = range

def pack(d):
    tup = tuple(d)
    return zip(cycle(tup[0:1]), tup[1:])

def window(seq, n=2):
    it = iter(seq)
    d = deque((next(it, None) for _ in range(n)), maxlen=n)
    yield pack(d)
    for e in it:
        d.append(e)
        yield pack(d)

for l in window(open('c:/working_file.txt', mode='r', encoding='utf8'),100):
    for a, b in l:
        print(a.strip() + '\t' + b.strip(), file=log)

Answer 1

基于旧文档的窗口示例,您可以使用以下内容:

from collections import deque
from itertools import cycle

try:
    xrange 
except NameError: # python3
    xrange = range

def pack(d):
    tup = tuple(d)
    return zip(cycle(tup[0:1]), tup[1:])

def window(seq, n=2):
    it = iter(seq)
    d = deque((next(it, None) for _ in xrange(n)), maxlen=n)
    yield pack(d)
    for e in it:
        d.append(e)
        yield pack(d)

演示:

>>> for l in window([1,2,3,4,5], 4):
...     for l1, l2 in l:
...         print l1, l2
...
1 2
1 3
1 4
2 3
2 4
2 5

所以,基本上你可以将文件传递给窗口以获得所需的结果:

window(open('C:/working_file.txt', mode='r', encoding='utf8'), 4)