python - 如何快速获取一个巨大的 csv 文件的最后一行(48M 行)？

Question

这个问题在这里已经有了答案:





How to read the last line of a file in Python?

(7 个回答)


6 个月前关闭。




我有一个 csv 文件，它会一直增长到大约 48M 行。
在向它添加新行之前，我需要阅读最后一行。
我尝试了下面的代码，但它太慢了，我需要一个更快的替代方案:

def return_last_line(filepath):    
    with open(filepath,'r') as file:        
        for x in file:
            pass
        return x        
return_last_line('lala.csv')

Answer 1

这是我的看法，在 python 中:
我创建了一个函数，让您选择最后几行，因为最后几行可能是空的。

def get_last_line(file, how_many_last_lines = 1):

    # open your file using with: safety first, kids!
    with open(file, 'r') as file:

        # find the position of the end of the file: end of the file stream
        end_of_file = file.seek(0,2)
        
        # set your stream at the end: seek the final position of the file
        file.seek(end_of_file)             
        
        # trace back each character of your file in a loop
        n = 0
        for num in range(end_of_file+1):            
            file.seek(end_of_file - num)    
           
            # save the last characters of your file as a string: last_line
            last_line = file.read()
           
            # count how many '\n' you have in your string: 
            # if you have 1, you are in the last line; if you have 2, you have the two last lines
            if last_line.count('\n') == how_many_last_lines: 
                return last_line
get_last_line('lala.csv', 2)

这个 lala.csv 有 4800 万行，比如在你的例子中。我花了 0 秒才拿到最后一行。