#!/usr/bin/python

import subprocess

p = subprocess.Popen(["tail", "-n 3", "passlist"], stdout=subprocess.PIPE)

output, err = p.communicate()

print  output

这个方法对我很有效

对于前5行，简单地做:

N=5
with open("data_file", "r") as file:
    for i in range(N):
       print file.next()

这对我很有效

f = open("history_export.csv", "r")
line= 5
for x in range(line):
    a = f.readline()
    print(a)

基于gnibbler的投票结果(2009年11月20日0:27):这个类将head()和tail()方法添加到文件对象。

class File(file):
    def head(self, lines_2find=1):
        self.seek(0)                            #Rewind file
        return [self.next() for x in xrange(lines_2find)]

    def tail(self, lines_2find=1):  
        self.seek(0, 2)                         #go to end of file
        bytes_in_file = self.tell()             
        lines_found, total_bytes_scanned = 0, 0
        while (lines_2find+1 > lines_found and
               bytes_in_file > total_bytes_scanned): 
            byte_block = min(1024, bytes_in_file-total_bytes_scanned)
            self.seek(-(byte_block+total_bytes_scanned), 2)
            total_bytes_scanned += byte_block
            lines_found += self.read(1024).count('\n')
        self.seek(-total_bytes_scanned, 2)
        line_list = list(self.readlines())
        return line_list[-lines_2find:]

用法:

f = File('path/to/file', 'r')
f.head(3)
f.tail(3)

我想通过读取整个文件来处理小于n行的文件

def head(filename: str, n: int):
    try:
        with open(filename) as f:
            head_lines = [next(f).rstrip() for x in range(n)]
    except StopIteration:
        with open(filename) as f:
            head_lines = f.read().splitlines()
    return head_lines

这要归功于约翰·拉·鲁伊和伊莲·伊利耶夫。使用异常句柄函数以获得最佳性能

修改1:感谢FrankM的反馈，处理文件存在和读取权限我们可以进一步增加

import errno
import os

def head(filename: str, n: int):
    if not os.path.isfile(filename):
        raise FileNotFoundError(errno.ENOENT, os.strerror(errno.ENOENT), filename)  
    if not os.access(filename, os.R_OK):
        raise PermissionError(errno.EACCES, os.strerror(errno.EACCES), filename)     
   
    try:
        with open(filename) as f:
            head_lines = [next(f).rstrip() for x in range(n)]
    except StopIteration:
        with open(filename) as f:
            head_lines = f.read().splitlines()
    return head_lines

您可以使用第二个版本，也可以使用第一个版本，稍后再处理文件异常。从性能的角度来看，检查是快速的，而且大部分是免费的

这里有另一个不错的解决方案与列表理解:

file = open('file.txt', 'r')

lines = [next(file) for x in range(3)]  # first 3 lines will be in this list

file.close()