《笨办法学Python》笔记14-----读写文件

上节中的代码没有关闭文件，这样并不好。

一、代码

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."

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()

这段代码的文件操作流程如下：

打开-清空-写入-关闭

文件打开模式见上一节。

文件写入后记得要close()。

二、更多的文件操作函数

close：关闭文件。跟你的编辑器的文件--》保存。。一个意思。

readline：读取文本文件中一行。

truncate：清空文件，请小心使用。

write：将字符串写入文件。

老办法，使用帮助命令查看各个函数：python -m pydoc file

1.close

close(...)

close() -> None or (perhaps) an integer.  Close the file.

Sets data attribute .closed to True.  A closed file cannot be used for

further I/O operations.  close() may be called more than once without

error.  Some kinds of file objects (for example, opened by popen())

may return an exit status upon closing.

一个已经被关闭的文件不能用于进一步的I/O操作

2.readline

readline(...)

readline([size]) -> next line from the file, as a string.

Retain newline.  A non-negative size argument limits the maximum

number of bytes to return (an incomplete line may be returned then).

Return an empty string at EOF.

可选参数限定最大返回字节数

3.truncate

truncate(...)

truncate([size]) -> None.  Truncate the file to at most size bytes.

Size defaults to the current file position, as returned by tell().

截断size大小的文件，size取决于当前文件的位置，这个位置可用tell()获取。

4.write

write(...)

write(str) -> None.  Write string str to file.

Note that due to buffering, flush() or close() may be needed before

the file on disk reflects the data written.

返回值None.注意由于缓冲的作用，在数据保存到磁盘之前需要flush()或者close()