python-open文件处理
python内置函数open()用于打开文件和创建文件对象
语法
open(name[,mode[,bufsize]])
name:文件名
mode:指定文件的打开模式
r:只读
w:写入
a:附加
r+,w+,a+同时支持输入输出操作
rb,wb+以二进制方式打开
bufsize:定义输出缓存
0表示无输出缓存
1表示使用缓冲
负数表示使用系统默认设置
正数表示使用近似指定大小的缓冲
#以只读方式打开text.txt文件，赋值给f1变量 >>> f1 = open('test.txt','r') #查看f1数据类型 >>> type(f1) <class '_io.TextIOWrapper'> #读取文件内容，以字符串形式返回 >>> f1.read() 'h1\nh2\nh3\nh4\nh5\nh6' #此时指针处于文件末尾，通过tell获取当前指针位置，通过seek重新指定指针位置 >>> f1.readline() '' >>> f1.tell() 22 >>> f1.seek(0) 0 #单行读取 >>> f1.readline() 'h1\n' #读取余下所有行，以列表方式返回 >>> f1.readlines() ['h2\n', 'h3\n', 'h4\n', 'h5\n', 'h6'] #文件名 >>> f1.name 'test.txt' #关闭文件 >>> f1.close() #文件写入 f2 = open('test.txt','w+') f2.write('hello') f2.close() #向文件追加内容 f3 = open('test.txt','a') f3.write('hello') f3.close() #通过flush，将缓冲区内容写入文件 #write将字符串值写入文件 f3 = open('test.txt','w+') for line in (i**2 for i in range(1,11)): f3.write(str(line)+'\n') f3.flush() #f3.close() #writelines将列表值写入文件 f3 = open('test.txt','w+') lines = ['11','22','33','44'] f3.writelines(lines) f3.seek(0) print(f3.readlines()) f3.close() #执行结果：['11223344'] >>> f3.closed True >>> f3.mode 'w+' >>> f3.encoding 'cp936'
Help on TextIOWrapper object: class TextIOWrapper(_TextIOBase) | Character and line based layer over a BufferedIOBase object, buffer. | | encoding gives the name of the encoding that the stream will be | decoded or encoded with. It defaults to locale.getpreferredencoding(False). | | errors determines the strictness of encoding and decoding (see | help(codecs.Codec) or the documentation for codecs.register) and | defaults to "strict". | | newline controls how line endings are handled. It can be None, '', | '\n', '\r', and '\r\n'. It works as follows: | | * On input, if newline is None, universal newlines mode is | enabled. Lines in the input can end in '\n', '\r', or '\r\n', and | these are translated into '\n' before being returned to the | caller. If it is '', universal newline mode is enabled, but line | endings are returned to the caller untranslated. If it has any of | the other legal values, input lines are only terminated by the given | string, and the line ending is returned to the caller untranslated. | | * On output, if newline is None, any '\n' characters written are | translated to the system default line separator, os.linesep. If | newline is '' or '\n', no translation takes place. If newline is any | of the other legal values, any '\n' characters written are translated | to the given string. | | If line_buffering is True, a call to flush is implied when a call to | write contains a newline character. | | Method resolution order: | TextIOWrapper | _TextIOBase | _IOBase | builtins.object | | Methods defined here: | | __getstate__(...) | | __init__(self, /, *args, **kwargs) | Initialize self. See help(type(self)) for accurate signature. | | __new__(*args, **kwargs) from builtins.type | Create and return a new object. See help(type) for accurate signature. | | __next__(self, /) | Implement next(self). | | __repr__(self, /) | Return repr(self). | | close(self, /) | Flush and close the IO object. | | This method has no effect if the file is already closed. | | detach(self, /) | Separate the underlying buffer from the TextIOBase and return it. | | After the underlying buffer has been detached, the TextIO is in an | unusable state. | | fileno(self, /) | Returns underlying file descriptor if one exists. | | OSError is raised if the IO object does not use a file descriptor. | | flush(self, /) | Flush write buffers, if applicable. | | This is not implemented for read-only and non-blocking streams. | | isatty(self, /) | Return whether this is an 'interactive' stream. | | Return False if it can't be determined. | | read(self, size=-1, /) | Read at most n characters from stream. | | Read from underlying buffer until we have n characters or we hit EOF. | If n is negative or omitted, read until EOF. | | readable(self, /) | Return whether object was opened for reading. | | If False, read() will raise OSError. | | readline(self, size=-1, /) | Read until newline or EOF. | | Returns an empty string if EOF is hit immediately. | | seek(self, cookie, whence=0, /) | Change stream position. | | Change the stream position to the given byte offset. The offset is | interpreted relative to the position indicated by whence. Values | for whence are: | | * 0 -- start of stream (the default); offset should be zero or positive | * 1 -- current stream position; offset may be negative | * 2 -- end of stream; offset is usually negative | | Return the new absolute position. | | seekable(self, /) | Return whether object supports random access. | | If False, seek(), tell() and truncate() will raise OSError. | This method may need to do a test seek(). | | tell(self, /) | Return current stream position. | | truncate(self, pos=None, /) | Truncate file to size bytes. | | File pointer is left unchanged. Size defaults to the current IO | position as reported by tell(). Returns the new size. | | writable(self, /) | Return whether object was opened for writing. | | If False, write() will raise OSError. | | write(self, text, /) | Write string to stream. | Returns the number of characters written (which is always equal to | the length of the string). | | ---------------------------------------------------------------------- | Data descriptors defined here: | | buffer | | closed | | encoding | Encoding of the text stream. | | Subclasses should override. | | errors | The error setting of the decoder or encoder. | | Subclasses should override. | | line_buffering | | name | | newlines | Line endings translated so far. | | Only line endings translated during reading are considered. | | Subclasses should override. | | ---------------------------------------------------------------------- | Methods inherited from _IOBase: | | __del__(...) | | __enter__(...) | | __exit__(...) | | __iter__(self, /) | Implement iter(self). | | readlines(self, hint=-1, /) | Return a list of lines from the stream. | | hint can be specified to control the number of lines read: no more | lines will be read if the total size (in bytes/characters) of all | lines so far exceeds hint. | | writelines(self, lines, /) | | ---------------------------------------------------------------------- | Data descriptors inherited from _IOBase: | | __dict__
*with
为了避免打开文件后忘记关闭，可以通过管理上下文，当with代码块执行完毕时，内部会自动关闭并释放文件资源。
with open("test.txt","a+") as f: f.write("hello world!")
