你所需要做的就是使用file对象作为迭代器。

for line in open("log.txt"):
    do_something_with(line)

在最近的Python版本中使用上下文管理器更好。

with open("log.txt") as fileobject:
    for line in fileobject:
        do_something_with(line)

这也会自动关闭文件。

我意识到这个问题在很久以前就已经回答过了，但是这里有一种并行的方法，而不会杀死您的内存开销(如果您试图将每一行放入池中，就会出现这种情况)。显然，将readJSON_line2函数替换为一些合理的函数——这只是为了说明这一点!

加速将取决于文件大小和你对每一行所做的事情-但最坏的情况是，对于一个小文件，只是用JSON阅读器读取它，我看到下面设置的性能与ST相似。

希望对大家有用:

def readJSON_line2(linesIn):
  #Function for reading a chunk of json lines
   '''
   Note, this function is nonsensical. A user would never use the approach suggested 
   for reading in a JSON file, 
   its role is to evaluate the MT approach for full line by line processing to both 
   increase speed and reduce memory overhead
   '''
   import json

   linesRtn = []
   for lineIn in linesIn:

       if lineIn.strip() != 0:
           lineRtn = json.loads(lineIn)
       else:
           lineRtn = ""
        
       linesRtn.append(lineRtn)

   return linesRtn




# -------------------------------------------------------------------
if __name__ == "__main__":
   import multiprocessing as mp

   path1 = "C:\\user\\Documents\\"
   file1 = "someBigJson.json"

   nBuffer = 20*nCPUs  # How many chunks are queued up (so cpus aren't waiting on processes spawning)
   nChunk = 1000 # How many lines are in each chunk
   #Both of the above will require balancing speed against memory overhead

   iJob = 0  #Tracker for SMP jobs submitted into pool
   iiJob = 0  #Tracker for SMP jobs extracted back out of pool

   jobs = []  #SMP job holder
   MTres3 = []  #Final result holder
   chunk = []  
   iBuffer = 0 # Buffer line count
   with open(path1+file1) as f:
      for line in f:
            
          #Send to the chunk
          if len(chunk) < nChunk:
              chunk.append(line)
          else:
              #Chunk full
              #Don't forget to add the current line to chunk
              chunk.append(line)
                
              #Then add the chunk to the buffer (submit to SMP pool)                  
              jobs.append(pool.apply_async(readJSON_line2, args=(chunk,)))
              iJob +=1
              iBuffer +=1
              #Clear the chunk for the next batch of entries
              chunk = []
                            
          #Buffer is full, any more chunks submitted would cause undue memory overhead
          #(Partially) empty the buffer
          if iBuffer >= nBuffer:
              temp1 = jobs[iiJob].get()
              for rtnLine1 in temp1:
                  MTres3.append(rtnLine1)
              iBuffer -=1
              iiJob+=1
            
      #Submit the last chunk if it exists (as it would not have been submitted to SMP buffer)
      if chunk:
          jobs.append(pool.apply_async(readJSON_line2, args=(chunk,)))
          iJob +=1
          iBuffer +=1

      #And gather up the last of the buffer, including the final chunk
      while iiJob < iJob:
          temp1 = jobs[iiJob].get()
          for rtnLine1 in temp1:
              MTres3.append(rtnLine1)
          iiJob+=1

   #Cleanup
   del chunk, jobs, temp1
   pool.close()

这是我找到的最佳解决方案，我在330 MB的文件上尝试了一下。

lineno = 500
line_length = 8
with open('catfour.txt', 'r') as file:
    file.seek(lineno * (line_length + 2))
    print(file.readline(), end='')

其中line_length是单行中的字符数。例如，“abcd”的行长为4。

我添加了2个行长来跳过'\n'字符并移动到下一个字符。

最好使用迭代器。 相关:fileinput -迭代多个输入流中的行。

从文档中可以看出:

import fileinput
for line in fileinput.input("filename", encoding="utf-8"):
    process(line)

这将避免将整个文件一次复制到内存中。

你所需要做的就是使用file对象作为迭代器。

for line in open("log.txt"):
    do_something_with(line)

在最近的Python版本中使用上下文管理器更好。

with open("log.txt") as fileobject:
    for line in fileobject:
        do_something_with(line)

这也会自动关闭文件。

在文件对象上使用for循环逐行读取。使用open(…)让上下文管理器确保文件读取后关闭:

with open("log.txt") as infile:
    for line in infile:
        print(line)