python - 文件访问预览

Question

我需要逐行读取文件，并且需要查看“下一行”，因此首先我将文件读入列表，然后循环浏览列表...不知何故，这似乎很粗鲁，构建列表可能是变得昂贵。

for line in open(filename, 'r'):
    lines.append(line[:-1])

for cn in range(0, len(lines)):
    line = lines[cn]
    nextline = lines[cn+1] # actual code checks for this eof overflow

必须有更好的方法来迭代线路，但我不知道如何向前看

Answer 1

您可能正在寻找类似 itertools 的pairwise recipe 的东西。

from itertools import tee, izip
def pairwise(iterable):
    "s -> (s0,s1), (s1,s2), (s2, s3), ..."
    a, b = tee(iterable)
    next(b, None)
    return izip(a, b)

with open(filename) as f: # Remember to use a with block so the file is safely closed after
    for line, next_line in pairwise(f):
        # do stuff

Answer 2

你可以这样做

last_line = None

for line in open(filename):                                                                  
    if last_line is not None:
        do_stuff(last_line, line) 
    last_line = line                                                        

Answer 3

您可以创建一个iterator并这样做：

f = open(filename, 'r')
g = open(filename, 'r')

y = iter(g.readlines())
y.__next__()

for line in f:
    print(line)
    try:
        print(y.__next__())
    except StopIteration:
        f.close()
        g.close()