那么：
def appoint_line(num,file):
with open(file,"r",encoding='utf-8') as f:
out = f.readlines[num-1]
return out
print(appoint_line(2,"c:/text.txt"))
以上示例为读取c盘下的text.txt文件的第二行
2.假如所谓“指定行”为开头几个字符，这里假设为三个
def appoint_line(file):
# appoimt_spring是指你指定行的前三个字符,你可以自行指定
appoint_spring = input(">>").strip()
with open(file,"r",encoding='utf-8') as f:
for line in f.readlines():
if line[0:3] == appoint_spring:
return line
print(appoint_line("c:/text.txt"))
以上示例为根据你输入的所指定行的前三个字符打印出c盘下的text.txt文件下的“指定行”
1.全部读到成列表然后选取行（容易超时，乱码等问题）2.利用迭代工具，代码如下：
from itertools import islice
with open('data.tsv', 'r') as f:
for line in islice(f, 1, None):
# process data
f.close()
修改islice函数中第2个参数n即可，表示读到f文件对象的第n行
#!/usr/bin/env python# coding: utf-8
def getfilelines(filename, eol='\n', buffsize=4096):
"""计算给定文件有多少行"""
with open(filename, 'rb') as handle:
linenum = 0
buffer = handle.read(buffsize)
while buffer:
linenum += buffer.count(eol)
buffer = handle.read(buffsize)
return linenum
def readtline(filename, lineno, eol="\n", buffsize=4096):
"""读取文件的指定行"""
with open(filename, 'rb') as handle:
readedlines = 0
buffer = handle.read(buffsize)
while buffer:
thisblock = buffer.count(eol)
if readedlines < lineno < readedlines + thisblock:
# inthisblock: findthe line content, and return it
return buffer.split(eol)[lineno - readedlines - 1]
elif lineno == readedlines + thisblock:
# need continue read line rest part
part0 = buffer.split(eol)[-1]
buffer = handle.read(buffsize)
part1 = buffer.split(eol)[0]
return part0 + part1
readedlines += thisblock
buffer = handle.read(buffsize)
else:
raise IndexError
def getrandomline(filename):
"""读取文件的任意一行"""
import random
return readtline(
filename,
random.randint(0, getfilelines(filename)),
)
if __name__ == "__main__":
import sys
import os
if len(sys.argv) == 1:
print getrandomline("/home/tim/documents/users.csv")
else:
for f in filter(os.path.isfile, sys.argv[1:]):
print getrandomline(f)
对于超大文件建议用逐行或分块的方式处理；逐行处理可能慢一些，但编码更简单清晰一点；上面给出的是按分块方式处理的。
