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 = ['','','','']
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!")