python - 如何在更正 if 语句之前打印 X 行

Question

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!

Answer 1

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)