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()

这适用于Python 2和3:

from itertools import islice

with open('/tmp/filename.txt') as inf:
    for line in islice(inf, N, N+M):
        print(line)

N = 10
with open("file.txt", "a") as file:  # the a opens it in append mode
    for i in range(N):
        line = next(file).strip()
        print(line)

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)

从Python 2.6开始，您可以利用IO基类中更复杂的函数。所以上面评分最高的答案可以改写为:

    with open("datafile") as myfile:
       head = myfile.readlines(N)
    print head

(你不必担心你的文件少于N行，因为没有StopIteration异常抛出。)

如果你想要一些明显(不需要在手册中查找深奥的东西)不需要导入就可以工作的东西，请尝试/except，并且可以在相当大范围的Python 2上工作。X版本(2.2至2.6):

def headn(file_name, n):
    """Like *x head -N command"""
    result = []
    nlines = 0
    assert n >= 1
    for line in open(file_name):
        result.append(line)
        nlines += 1
        if nlines >= n:
            break
    return result

if __name__ == "__main__":
    import sys
    rval = headn(sys.argv[1], int(sys.argv[2]))
    print rval
    print len(rval)