Help on class file in module __builtin__:

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.

 |  

 |  ‘U‘ cannot be combined with ‘w‘ or ‘+‘ mode.

 |  

 |  Methods defined here:

 |  

 |  __delattr__(...)

 |      x.__delattr__(‘name‘) <==> del x.name

 |  

 |  __enter__(...)

 |      __enter__() -> self.

 |  

 |  __exit__(...)

 |      __exit__(*excinfo) -> None.  Closes the file.

 |  

 |  __getattribute__(...)

 |      x.__getattribute__(‘name‘) <==> x.name

 |  

 |  __init__(...)

 |      x.__init__(...) initializes x; see help(type(x)) for signature

 |  

 |  __iter__(...)

 |      x.__iter__() <==> iter(x)

 |  

 |  __repr__(...)

 |      x.__repr__() <==> repr(x)

 |  

 |  __setattr__(...)

 |      x.__setattr__(‘name‘, value) <==> x.name = value

 |  

 |  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.

 |  

 |  fileno(...)

 |      fileno() -> integer "file descriptor".

 |      

 |      This is needed for lower-level file interfaces, such os.read().

 |  

 |  flush(...)

 |      flush() -> None.  Flush the internal I/O buffer.

 |  

 |  isatty(...)

 |      isatty() -> true or false.  True if the file is connected to a tty device.

 |  

 |  next(...)

 |      x.next() -> the next value, or raise StopIteration

 |  

 |  read(...)

 |      read([size]) -> read at most size bytes, returned as a string.

 |      

 |      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.

 |  

 |  readinto(...)

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

 |  

 |  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.

 |  

 |  readlines(...)

 |      readlines([size]) -> list of strings, each a line from the file.

 |      

 |      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.

 |  

 |  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.

 |  

 |  tell(...)

 |      tell() -> current file position, an integer (may be a long integer).

 |  

 |  truncate(...)

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

 |      

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

 |  

 |  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.

 |  

 |  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.

 |  

 |  xreadlines(...)

 |      xreadlines() -> returns self.

 |      

 |      For backward compatibility. File objects now include the performance

 |      optimizations previously implemented in the xreadlines module.

 |  

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

 |  Data descriptors defined here:

 |  

 |  closed

 |      True if the file is closed

 |  

 |  encoding

 |      file encoding

 |  

 |  errors

 |      Unicode error handler

 |  

 |  mode

 |      file mode (‘r‘, ‘U‘, ‘w‘, ‘a‘, possibly with ‘b‘ or ‘+‘ added)

 |  

 |  name

 |      file name

 |  

 |  newlines

 |      end-of-line convention used in this file

 |  

 |  softspace

 |      flag indicating that a space needs to be printed; used by print

 |  

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

 |  Data and other attributes defined here:

 |  

 |  __new__ = <built-in method __new__ of type object>

 |      T.__new__(S, ...) -> a new object with type S, a subtype of T

file(name[, mode[, buffering]])

Constructor function for the file type, described further in section File Objects. The constructor’s arguments are the same as those of the open() built-in function described below.

When opening a file, it’s preferable to use open() instead of invoking this constructor directly. file is more suited to type testing (for example, writing isinstance(f, file)).

中文说明：

读出一个文件的内容。

file()函数是2.2中新增的函数，它与open()函数一样，相当于open()的别名，不过比open()更直观一些。

lines = file(filename).readlines()

for line in lines:

    print line

序号  方法及描述

1 file.close()

关闭文件。关闭后文件不能再进行读写操作。

2 file.flush()

刷新文件内部缓冲，直接把内部缓冲区的数据立刻写入文件, 而不是被动的等待输出缓冲区写入。

3 file.fileno()

返回一个整型的文件描述符(file descriptor FD 整型), 可以用在如os模块的read方法等一些底层操作上。

4 file.isatty()

如果文件连接到一个终端设备返回 True，否则返回 False。

5 file.next()

返回文件下一行。

6 file.read([size])

从文件读取指定的字节数，如果未给定或为负则读取所有。

7 file.readline([size])

读取整行，包括 "\n" 字符。

8 file.readlines([sizehint])

读取所有行并返回列表，若给定sizeint>0，返回总和大约为sizeint字节的行, 实际读取值可能比sizhint较大, 因为需要填充缓冲区。

9 file.seek(offset[, whence])

设置文件当前位置

10 file.tell()

返回文件当前位置。

11 file.truncate([size])

截取文件，截取的字节通过size指定，默认为当前文件位置。

12 file.write(str)

将字符串写入文件，没有返回值。

13 file.writelines(sequence)

向文件写入一个序列字符串列表，如果需要换行则要自己加入每行的换行符。

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python内置函数4-file()