python之如何在更正 if 语句之前打印 X 行

我是 Python 的新手，对我在众多网页中找到的内容只有分段的千篇一律的知识。

话虽这么说，我正在尝试在一个文件(~10k 行)中搜索我编写的一组类似“过滤器”的条件，然后我希望它打印符合条件的行和符合条件的行它之前的 X 行数。

我创建了以下脚本来打开所述文件，逐行迭代，并将满足过滤条件的行打印到输出文件，但是我不知道如何将其合并到当前脚本中。

import os 
 
output_file = 'Output.txt' 
filename = 'BigFile.txt'                  
 
numLines = 0 
numWords = 0 
numChrs = 0 
numMes = 0 
 
f1 = open(output_file, 'w') 
print 'Output File has been Opened' 
 
with open(filename, 'r') as file: 
   for line in file: 
      wordsList = line.split() 
      numLines += 1 
      numWords += len(wordsList) 
      numChrs += len(line) 
 
      if "X" in line and "Y" not in line and "Z" in line: 
          numMes += 1 
          print >>f1, line 
          print 'Object found and Catalogued in Output.txt'                           
 
print "Lines: %i\nWords: %i\nCharacters: %i" % (numLines, numWords, numChrs) 
print >>f1, "Lines: %i\nWords: %i\nCharacters: %i" % (numLines, numWords, numChrs) 
 
print "There are a total of %i thing in this file" % (numMes) 
print >>f1, "There are a total of %i things in this file" % (numMes) 
 
f1.close() 
 
print 'Output Files have been Closed' 

我的第一个猜测是使用 line.enumeration 但我认为我不能只声明类似 lines - 5 的内容来打印 之前的 5 行>行:

lines = f1.enumeration() 
if "blah blah" in line and "so so" not in line: 
    print >>f1, lines 
    print >>f1, [lines - 5] 

不过最精彩的部分还在后面，因为我必须获取 Output.txt 文件并与另一个文件进行比较，以输出两个文件中的匹配条件……但一次一个步骤，对吗？

- 也可以随意添加“正确”技术的简介...我相信这个脚本可以用更好的方式编写，所以请对我做错的任何事情进行教育。

在此先感谢您的帮助!

更新: 由于以下帮助，已成功实现修复:

import os 
 
output_file = 'Output.txt' 
filename = 'BigFile.txt'                  
 
numLines = 0 
numWords = 0 
numChrs = 0 
 
numMulMes = 0 
 
last5 = [] 
 
f1 = open(output_file, 'w') 
print 'Output Files have been Opened' 
 
with open(filename, 'r') as file: 
    for line in file: 
        wordsList = line.split() 
        numLines += 1 
        numWords += len(wordsList) 
        numChrs += len(line) 
        last5[:] = last5[-5:]+[line]  
        if "X" in line and "Y" not in line and "Z" not in line: 
            del last5[1:5]           ###the missing piece of the puzzle! 
            numMulMes += 1 
            print >>f1, last5 
            print 'Object found and Catalogued in Output.txt' 
 
print "Lines: %i\nWords: %i\nCharacters: %i" % (numLines, numWords, numChrs) 
print >>f1, "Lines: %i\nWords: %i\nCharacters: %i" % (numLines, numWords, numChrs) 
 
print "There are a total of %i messages in this file" % (numMulMes) 
print >>f1, "There are a total of %i messages in this file" % (numMulMes) 
 
f1.close() 
f3.close() 
 
print 'Output Files have been Closed' 

我一直试图通过另一个单独的脚本修改输出文件，并且在最长的时间内我一直在与 str vs lst 操作和错误问题作斗争。刚决定回到原来的剧本，一时兴起把它扔进去，中提琴。

感谢您将我推向正确的方向，从那里很容易弄明白!

请您参考如下方法:

您自己解决了大部分问题(计算字数、行数、行号等) - 您可以在浏览文件时简单地记住最后 n 行。

例子:

t = """"zero line 
one line 
two line 
three line 
four line  
five line  
six line 
seven line  
eight line 
"""  
 
last5 = [] # memory cell 
for l in t.split("\n"):  # similar to your for line in file:  
    last5[:] = last5[-4:]+[l] # keep last 4 and add current line, inplace list mod  
 
    if "six" in l: 
        print last5 

你也可以看看deque并指定一个最大长度(你需要导入它)

from collections import deque 
 
last5 = deque(maxlen=5) 
for l in t.split("\n"):  
    last5.append(l) # will automatically only keep 5 (maxlen) 
 
    if "six" in l: 
        print last5 

输出:

 # list version 
 ['two line', 'three line', 'four line ', 'five line ', 'six line']  
 
 # deque version 
 deque(['two line', 'three line', 'four line ', 'five line ', 'six line'], maxlen=5)