python 从文件中读取特定行并继续

我正在尝试从文件中读取特定行并在结束每个 block 的进程后继续读取。 比方说，我在一个文件中有 19000 行。每次，我都会提取前 19 行，对这些行进行一些计算并将输出写入另一个文件。然后我将再次提取接下来的 19 行并进行相同的处理。因此，我尝试通过以下方式提取行:

n=19 
x = defaultdict(list) 
 
i=0 
 
fp = open("file") 
for next_n_lines in izip_longest(*[fp] *n): 
    lines = next_n_lines 
 
    for i, line in enumerate(lines):  
        do calculation 
    write results 

这里的代码适用于第一个 block 。你们中的任何人都可以帮助我，我该如何继续下一个 n block ？非常感谢!

请您参考如下方法:

您的代码已经以 19 行为一组提取行，所以我不确定您的问题是什么。

我可以稍微清理一下您的解决方案，但它的作用与您的代码相同:

from itertools import izip_longest 
 
# grouping recipe from itertools documentation 
def grouper(n, iterable, fillvalue=None): 
    "Collect data into fixed-length chunks or blocks" 
    # grouper(3, 'ABCDEFG', 'x') --> ABC DEF Gxx 
    args = [iter(iterable)] * n 
    return izip_longest(fillvalue=fillvalue, *args) 
 
def process_chunk(chunk): 
    "Return sequence of result lines.  Chunk must be iterable." 
    for i, line in enumerate(chunk): 
        yield 'file-line {1:03d}; chunk-line {0:02d}\n'.format(i, int(line)) 
    yield '----------------------------\n' 

下面是一些测试代码，演示了每一行都被访问了:

from StringIO import StringIO 
 
class CtxStringIO(StringIO): 
    def __enter__(self): 
        return self 
    def __exit__(self, *args): 
        return False 
 
infile = CtxStringIO(''.join('{}\n'.format(i) for i in xrange(19*10))) 
outfile = CtxStringIO() 
 
 
# this should be the main loop of your program. 
# just replace infile and outfile with real file objects 
with infile as ifp, outfile as ofp: 
    for chunk in grouper(19, ifp, '\n'): 
        ofp.writelines(process_chunk(chunk)) 
 
# see what was written to the file 
print ofp.getvalue() 

此测试用例应打印如下行:

file-line 000; chunk-line 00 
file-line 001; chunk-line 01 
file-line 002; chunk-line 02 
file-line 003; chunk-line 03 
file-line 004; chunk-line 04 
... 
file-line 016; chunk-line 16 
file-line 017; chunk-line 17 
file-line 018; chunk-line 18 
---------------------------- 
file-line 019; chunk-line 00 
file-line 020; chunk-line 01 
file-line 021; chunk-line 02 
... 
file-line 186; chunk-line 15 
file-line 187; chunk-line 16 
file-line 188; chunk-line 17 
file-line 189; chunk-line 18 
----------------------------