# -- coding: utf-8 --
# 从sys模块导入argv函数
from sys import argv
# 利用argv函数，把 argv 中的东西解包，将所有的参数依次赋予左边的变量名
script, input_file = argv
# 自定义一个函数，读取f的内容
def print_all(f):
print f.read()
# 自定义函数，使用file中的seek方法来移动文件游标，用于依次读取文件行的功能
def rewind(f):
f.seek(0)
# 该脚本的主函数，用于打印文件每一行的内容
def print_a_line(line_count, f):
print "No.", line_count, f.readline()
# 使用file中的open方法来打开文件
current_file = open(input_file)
print "First let‘s print the whole file:\n"
# 使用自定义的函数print_all来读取打开的文件内容
print_all(current_file)
print "Now let‘s rewind, kind of like a tape."
# 使用上面自定义的函数rewind
rewind(current_file)
print "Let‘s print three lines:"
# 定义一个变量，每打印完一行就加1，把这个变量作为print_a_line函数的参数，调用print_a_line函数可以依次打印每一行。
# 下面的几行代码可以采用循环来写，以减少代码长度。
current_line = 1
print "Now Current line is : %d" % current_line
print_a_line(current_line, current_file)
current_line = current_line + 1
print "Now Current line is : %d" % current_line
print_a_line(current_line, current_file)
current_line = current_line + 1
print "Now Current line is : %d" % current_line
print_a_line(current_line, current_file)
使用python的帮助来查询seek方法的内容
python -m pydoc fileseek(...)
seek(offset[, whence]) -> None. Move to new file position.
Argument offset is a byte count. Optional argument whence defaults to 0 (offset from start of file, offset should be >= 0); other values are 1(move relative to current position, positive or negative), and 2 (moverelative to end of file, usually negative, although many platforms allowseeking beyond the end of a file). If the file is opened in text mode, only offsets returned by tell() are legal. Use of other offsets causes undefined behavior. Note that not all file objects are seekable.
利用 += 来改变变量的值。
a = 1
print a
a += 1
print a
a += 2
print a得到的结果如下：
PS C:\python> python No20plus.py
1
2
4原文地址：http://blog.51cto.com/6150141/2072958
