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
#以只读⽅式打开⽂件，赋值给f1变量
>>> f1 = open('','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)
#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
''
#关闭⽂件
>>> f1.close()
#⽂件写⼊
f2 = open('','w+')
f2.write('hello')
f2.close()
#向⽂件追加内容
f3 = open('','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('','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('','w+')
lines = ['11','22','33','44']
f3.writelines(lines)
f3.seek(0)
adlines())
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 preferredencoding(False). |
|  errors determines the strictness of encoding and decoding (see
|  help(codecs.Codec) or the documentation ister) 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
writelines()方法将什么写入文件|  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) pe
|      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__
View Code
*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("","a+") as f:
f.write("hello world!")

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