如何在更正if语句之前打印X行

你自己解决了大部分问题(数单词、行、行号等) -在浏览文件时,只需记住最后n行即可。

示例:

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

您还可以查看 deque 并指定最大长度(需要导入)

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) 

这里的解决方案与@PatricArtner建议的相同,但使用了环形缓冲区。它可能(也可能不是,我没有检查)在处理大文件时工作得更快。 想法很简单:我们可以创建一个具有所需大小(您应该保留的行数)和当前录制位置计数器的列表 cnt 。对于每一行,我们应该将cnt增加1,并根据缓冲区的大小进行模运算。因此 cnt公司 正在列表中循环。例如,如果列表大小为5 cnt = (cnt+1)%5 将给予 0 1 2 3 4 0 1 2 等等每一步 cnt公司 将指向列表中最旧的数据,这些数据将被新数据替代。下面是实现的一个示例。

t = """"zero line
six line - surprize 
one line
two line
three line
four line 
five line 
six line
seven line 
eight line
""" 


last5 = [None,None,None,None,None]
cnt = 0
for l in t.split("\n"):
  last5[cnt]=l
  if 'six' in l:
    print last5[(cnt+1)%5]
    print last5[(cnt+2)%5]
    print last5[(cnt+3)%5]
    print last5[(cnt+4)%5]
    print last5[(cnt+0)%5]
    print
  cnt = (cnt+1)%5

输出非常简单:

None
None
None
"zero line
six line - surprize 

two line
three line
four line 
five line 
six line

注: 如果你从一个文件中读取,而这个文件非常大,你需要保留的字符串非常大(例如,基因序列),并且你的情况不会经常触发,那么要聪明,不要在内存中保留字符串。在文件中创建最后一个字符串开始的位置列表,如果需要,请重新读取它们。下面是一个如何使其非常快速的示例。。。

from numpy import random as rnd

print "Creating the file ...."
DNA=["G","C","T","A"]
with open("bigdatafile","w") as fd:
    for i in xrange(5000):
        fd.write("".join([ DNA[rnd.randint(4)] for x in xrange(2000)])+"\n")
print "DONE"
print
print "SEARCHING GGGGGGGGGGG"
last5, cnt = [0,0,0,0,0], 1
with open("bigdatafile","r") as fd:
    for i,l in enumerate(fd.readlines()):
        last5[cnt] = last5[(cnt+4)%5]+len(l)
        if "GGGGGGGGGGG" in l:
            print "FIND!"
            fd.seek(last5[(cnt+1)%5])
            print fd.read(last5[cnt]-last5[(cnt+1)%5])
        cnt = (cnt+1)%5

我把东西输出到字典,而不是写入文件。处理完整个文件后,汇总数据字典将以 json .使用Artner的测试文件。

import os
import json

output_file = 'Output.txt'
filename = 'BigFile.txt'                 

#initiate output container
outDict = {}
for fields in ['numLines', 'numWords', 'numChrs', 'numMes']:
    outDict[fields] = 0

outDict['lineNum'] = []    

with open(filename, 'r') as file:
    for line in file:
      wordsList = line.strip().split("\s")
      outDict['numLines'] += 1
      outDict['numWords'] += len(wordsList)
      outDict['numChrs'] += len(line)

      #find items in the line
      if "t" in line:
          outDict['numMes'] += 1
          #save line number
          outDict['lineNum'].append(outDict['numLines']) 
          #save line content
          outDict['lineList'].append(line)

#record output          
with open(output_file, 'w') as f1:
    f1.write(json.dumps(outDict))    

##print lines of desire
#x number of lines before
x=5    
with open(filename, 'r') as file:
    for i, line in enumerate(file):
        #iterate over line numbers for which condition is met
        for j in range(0,len(outDict['lineNum'])):
            #if line number is between found line num and line num minus x, print
            if (outDict['lineNum'][j]-x) <= i <= outDict['lineNum'][j]:
                print(line)

自从我在 comments ,下面是如何在*nix机器上使用 grep 的 context line control 功能。

首先假设您有以下文本文件 test.txt :

zero line
one line
two line
three line
four line 
five line 
six line
seven line 
eight line

如果你想 N 在匹配之前,可以使用 -B 选项例如,对于之前的5行 "six" :

$ grep -B 5 six test.txt 
one line
two line
three line
four line 
five line 
six line

还有 -A 您可以使用的选项 N 比赛后的线条和 -C 您可以使用它 N 前后的线条。