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Python：file/file-like对象方法详解【单个文件读写】

2024-07-06 14:25:19 224人阅读

IO中读写文件操作方法汇总！----The_Third_Wave的学习笔记！

本文由@The_Third_Wave（Blog地址：http://blog.csdn.net/zhanh1218）原创。不定期更新，有错误请指正。

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class file(object)

| file(name[, mode[, buffering]]) -> file object
|
| Open a file. The mode can be ‘r‘, ‘w‘ or ‘a‘ for reading (default), writing or appending. The file will be created if it doesn‘t exist when opened for writing or appending; it will be truncated when opened for writing. Add a ‘b‘ to the mode for binary files. Add a ‘+‘ to the mode to allow simultaneous reading and writing. If the buffering argument is given, 0 means unbuffered, 1 means line buffered, and larger numbers specify the buffer size. The preferred way to open a file is with the builtin open() function. Add a ‘U‘ to mode to open the file for input with universal newline support. Any line ending in the input file will be seen as a ‘\n‘ in Python. Also, a file so opened gains the attribute ‘newlines‘; the value for this attribute is one of None (no newline read yet), ‘\r‘, ‘\n‘, ‘\r\n‘ or a tuple containing all the newline types seen.

打开文件。默认为reading模式（r），mode参数可以为 ‘r‘-reading , ‘w‘-writing or ‘a‘ -appending（追加）。当为writing模式或者appending模式时如果文件不存在可能被创建。writing模式时文件可能被截断。‘b‘模式用于二进制文件。‘+‘模式用于允许同时读写文件。

buffering：0，无缓冲；1，一行缓冲，数字越大，意味着缓冲区越大。

打开文件推荐内置函数open()。‘U‘模式为通用换行符支持输入打开文件。在Python中任何行结束符在输入文件将被视为‘\n‘。同时，文件打开增加属性‘newlines‘；此属性的值为None（没有新行可读时），‘r‘，‘n‘，‘\r\n‘或一个元组包含所有换行符的类型。

| ‘U‘ cannot be combined with ‘w‘ or ‘+‘ mode.
| ‘U‘不能和‘w‘或者‘+‘模式一起使用。

Methods defined here:

| close(...)

| close() -> None or (perhaps) an integer. Close the file.
| 关闭文件

| 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.

设置数据属性.closed()为真。关闭的文件不能用于进一步的I/O操作（关闭文件就没办法在操作了）！无错误时可以被调用1次以上。某些种类的文件对象可能在关闭时返回一个状态值（例如：popen()打开的文件对象）。【注：os.popen()】

| fileno(...)

| fileno() -> integer "file descriptor".
| 返回值为整数（文件描述符）
| This is needed for lower-level file interfaces, such os.read().
| 需要1个低级的文件接口，例如os.read()

| flush(...)

| flush() -> None. Flush the internal I/O buffer 把缓冲区的内容写入磁盘！（write()之后需要用到）

| isatty(...)

| isatty() -> true or false. True if the file is connected to a tty device.返回文件是否是一个终端设备文件【unix系统中使用】。

| next(...)

| x.next() -> the next value, or raise StopIteration【也就是生成器的方法，返回下一行。】
|

| read(...)

| read([size]) -> read at most size bytes, returned as a string.
| 读取数据，返回字符串，可以指定大小。

| If the size argument is negative or omitted, read until EOF is reached. Notice that when in non-blocking mode, less data than what was requested may be returned, even if no size parameter was given.

如果size为负数或者缺省，读取整个文件。注意在非阻塞模式下，数据返回的可能比实际请求返回的少，及时size参数没有给定（也就是缺省状态）！

| readinto(...)

| readinto() -> Undocumented. Don‘t use this; it may go away.
|

| readline(...)

| readline([size]) -> next line from the file, as a string.
| 读取文件中的下一行，返回字符串

| 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.

保持新行。非负的size参数限制返回的最大的字节数（也就是可能会返回不完整的行）。文件结束时返回空字符串！

| readlines(...)

| readlines([size]) -> list of strings, each a line from the file.
| 返回每行数据的字符串列表
| Call readline() repeatedly and return a list of the lines so read. The optional size argument, if given, is an approximate bound on the total number of bytes in the lines returned.不断调用readline()方法并且返回一个每行数据（str）组成的list。【list(f)效果相同；size参数2.7.6实测使用没变化和read()读出来的相同，待进一步确定。】

| seek(...)

| 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 (move relative to end of file, usually negative, although many platforms allow seeking 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.

| 将文件打操作标记移到offset的位置。这个offset一般是相对于文件的开头来计算的，一般为正数。但如果提供了whence参数就不一定了，whence可以为0表示从头开始计算，1表示以当前位置为原点计算。2表示以文件末尾为原点进行计算。需要注意，如果文件以a或a+的模式打开，每次进行写操作时，文件操作标记会自动返回到文件末尾。

| tell(...)

| tell() -> current file position, an integer (may be a long integer).
| 返回文件当前位置，一个整数（可能是一个长整数）。【也就是一行一行读写文件时，现在光标所在位置（以文件开头为原点）】

| truncate(...)

| truncate([size]) -> None. Truncate the file to at most size bytes.按size的值截取文件。
|
| Size defaults to the current file position, as returned by tell()。【说明太简单，待确定】
|

| write(...)

| write(str) -> None. Write string str to file.
| 写字符串到文件，返回值为None
| Note that due to buffering, flush() or close() may be needed before the file on disk reflects the data written.执行flush()或者close()之后才能真正写到文件。

| writelines(...)

| writelines(sequence_of_strings) -> None. Write the strings to the file.
|
| Note that newlines are not added. The sequence can be any iterable object producing strings. This is equivalent to calling write() for each string.请注意，没有添加新行。sequence_of_strings可为字符串构成的迭代器。这相当于调用write()写每个字符串。【不会自动换行，也就是说不会自动添加换行符；sequence_of_strings可以使list、tuple、dict（保持迭代器中内容为str）。】

| xreadlines(...)

| xreadlines() -> returns self.
| 返回自身
| For backward compatibility. File objects now include the performance optimizations previously implemented in the xreadlines module.向后兼容。文件对象包括性能优化以前实施的xreadlines模块。
|

| ----------------------------------------------------------------------

文件读写

一、普通型

>>> f = open("C:\\Users\\admin\\Desktop\\222.txt",'r')
>>> print f.read()
@The Third Wave（Blog地址：http://blog.csdn.net/zhanh1218)文件读写！
>>> f.closed
False
>>> f.close()
>>> f.closed
True
>>>

每次读完文件后，需要close()方法关闭文件对象。文件使用完毕后必须关闭，因为：文件对象会占用操作系统的资源；操作系统同一时间能打开的文件数量有限。

二、try--except--finally

>>> try:
	f = open("C:\\Users\\admin\\Desktop\\222.txt",'r')
	print f.read()
	print f.closed
except:
	print "error"
	raise
finally:
	if f:
	    f.close()
	print f.closed

	
@The Third Wave（Blog地址：http://blog.csdn.net/zhanh1218)文件读写！
False
True
>>>

比较麻烦！

三、文艺型

使用with as语句，推荐！！！

>>> with open("C:\\Users\\admin\\Desktop\\222.txt",'r') as f:
	print f.read()
	print f.closed

	
@The Third Wave（Blog地址：http://blog.csdn.net/zhanh1218)文件读写！
False
>>> f.closed
True
>>>