跟着笨方法学python个教程学习，边学边做习题边记录。
新手学python-笨方法学Python-ex16-读写文件件 - 学习记录
课程内容：
了解各种文件相关的命令（方法/函数）：
close - 关闭文件。跟你编辑器的 文件->保存.. 一个意思。
read - 读取文件内容。你可以把结果赋给一个变量。
readline - 读取文本文件中的一行。
truncate - 清空文件，请小心使用该命令。
write(stuff) - 将stuff写入文件。
这是你现在该知道的重要命令。有些命令需要接受参数，这对我们并不重要。你只要记住write的用法就可以了。write需要接收一个字符串作为参数，从而将该字符串写入文件。
让我们来使用这些命令做一个简单的文本编辑器吧：
from sys import argv
script, filename = argv
print "We're going to erase %r." % filename
print "If you don't want that, hit CTRL-C(^C)."
print "If you do want that, hit RETURN."
raw_input("?")
print "Opening the file..."
target = open(filename, 'w')
print "Truncating the file. Goodbye!"
target.truncate()
print "Now I'm going to ask you for three lines."
line1 = raw_input("line 1: ")
line2 = raw_input("line 2: ")
line3 = raw_input("line 3: ")
print "I'm going to write these to the file."
target.write(line1)
target.write("\n")
target.write(line2)
target.write("\n")
target.write(line3)
target.write("\n")
print "And finally,we close it."
target.close()
这个文件是够大的，大概是你键入过的最大的文件。所以慢慢来，仔细检查，让它能运行起来。
有一个小技巧可以让你的脚本一部分一部分地运行起来。先写1-8行，让它运行起来；再多运行5行，再接着多运行几行，一次类推，直到整个脚本运行起来为止。
运行该脚本：
$python ex16.py ex16-sample.txt
We're going to erase 'ex16-sample.txt'.
If you don't want that, hit CTRL-C(^C).
If you do want that, hit RETURN.
?
Opening the file...
Truncating the file. Goodbye!
Now I'm going to ask you for three lines.
line 1: the 1st line for test.
line 2: the 2nd line.
line 3: the last line for check...
I'm going to write these to the file.
And finally,we close it.
$
接下来打开你新建的文件（我的是ex16-sample.txt），看看里面的内容。
the 1st line for test.
the 2nd line.
the last line for check...
加分习题：
1.如果你觉得自己没有弄懂的话，用我们的老办法，在每一行之前加上注解，为自己理清思路。就算不能理清思路，你也可以知道自己究竟具体哪里没弄明白。
2.写一个和上一个练习类似的脚本，使用 read 和 argv 读取你刚才新建的文件。
from sys import argv
script, filename = argv
print "We are going to erase %r." % filename
print "If you do not want that, hit CTRL-C(^C)."
print "If you do want that, hit RETURN."
raw_input("?")
print "Opening the file..."
target = open(filename, 'w')
print "Truncating the file. GoodBye..."
target.truncate()
print "Now I'm going to ask you for three lines."
line1 = raw_input("line 1: ")
line2 = raw_input("line 2: ")
line3 = raw_input("line 3: ")
print "I'm going to write these to the file."
target.write(line1)
target.write("\n")
target.write(line2)
target.write("\n")
target.write(line3)
target.write("\n")
print "And finally,we close it."
target.close()
print "To see the new file content."
txt = open(filename)
print txt.read()
txt.close()
运行该脚本：
$python ex16-2.py ex16-sample.txt
We are going to erase 'ex16-sample.txt'.
If you do not want that, hit CTRL-C(^C).
If you do want that, hit RETURN.
?
Opening the file...
Truncating the file. GoodBye...
Now I'm going to ask you for three lines.
line 1: abc
line 2: 123
line 3: hi hello
I'm going to write these to the file.
And finally,we close it.
To see the new file content.
abc
123
hi hello
$
3.文件中重复的地方太多了。试着用一个 target.write() 将 line1, line2, line3 打印出来，你可以使用字符串、格式化字符、以及转义字符。
3.1 将6行target.write()换成target.write("%s \n %s \n %s \n" ) % (line1, line2, line3)，运行程序，出错
TypeError: unsupported operand type(s) for %: 'NoneType' and 'tuple'
3.2上网查了一下，字符串连接用 + ：
将6行target.write()换成 target.write(line1 + "\n" + line2 + "\n" + line3 + "\n") ，成功：
from sys import argv
script, filename = argv
print "We're going to erase %r." % filename
print """
If you do not want that, hit CTRL-C(^C).
If you do want that, hit RETURN.
"""
print "Opening the file ..."
target = open(filename, 'w')
print "Truncating the file ..."
target.truncate()
print "Now I'm going to ask you for three lines."
line1 = raw_input("line 1: ")
line2 = raw_input("line 2: ")
line3 = raw_input("line 3: ")
print "I'm going to write these to the file."
#target.write(line1 "\n" line2 "\n" line3 "\n")
target.write(line1 + "\n" + line2 + "\n" + line3 + "\n")
print "And finally, we close it."
target.close()
print "Print the new contents of the file..."
newtxt = open(filename)
print newtxt.read()
newtxt.close
运行该程序：
$python ex16-3.py ex16-sample.txt
We're going to erase 'ex16-sample.txt'.
If you do not want that, hit CTRL-C(^C).
If you do want that, hit RETURN.
Opening the file ...
Truncating the file ...
Now I'm going to ask you for three lines.
line 1: test1
line 2: test2
line 3: test3
I'm going to write these to the file.
And finally, we close it.
Print the new contents of the file...
test1
test2
test3
$
4.找出为什么我们需要给 open 多赋予一个 'w' 参数。提示： open 对于文件的写入操作态度是安全第一，所以你只有特别指定以后，它才会进行写入操作。
默认只读
至此，笨方法学Python-ex16-读写文件这一小节的学习结束了。