python 3-5-1 关于文件的操作-open/read/readlines/seek/write/writelines

关于文件的操作

f = open(“test.sh”) f是一个可迭代对象

readlines() 方法是将文件的所有内容放进列表中,如果文件非常大，内存消耗是个极大的问题

readline() 既然open()返回的是一个可迭代对象,则可以用for循环来逐行取出

seek() 当readlines 或者readline迭代结束以后，文件的指针就指向了文件尾，可以通过f.seek(0)将文件指针指向文件头

read()读取字节数，如果没有给定字节数，则会直接读到最后

write() 写入字符串到文件

writelines()写入多行字符串到文件

from collections import Iterable
isinstance(f,Iterable)
f = open("test.sh")
for line in f:
print line

关于文件操作帮助信息

>>> help(f)
Help on file object:

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