Python的命令行帮助文档

目的：不知道如何使用模块的问题 对自学有帮助
有三个工具可使用dir（）、help（）和__doc__
1、dir函数式可以查看对象的属性，使用方法很简单
查看sys的所有属性
>>> import sys
>>> dir(sys)
['__displayhook__', '__doc__', '__egginsert', '__excepthook__', '__name__', '__package__', '__plen', '__stderr__', '__stdin__', '__stdout__', '_clear_type_cache', '_current_frames', '_getframe', 'api_version', 'argv', 'builtin_module_names', 'byteorder', 'call_tracing', 'callstats', 'copyright', 'displayhook', 'dont_write_bytecode', 'exc_clear', 'exc_info', 'exc_type', 'excepthook', 'exec_prefix', 'executable', 'exit', 'flags', 'float_info', 'getcheckinterval', 'getdefaultencoding', 'getdlopenflags', 'getfilesystemencoding', 'getprofile', 'getrecursionlimit', 'getrefcount', 'getsizeof', 'gettrace', 'hexversion', 'last_traceback', 'last_type', 'last_value', 'maxint', 'maxsize', 'maxunicode', 'meta_path', 'modules', 'path', 'path_hooks', 'path_importer_cache', 'platform', 'prefix', 'ps1', 'ps2', 'py3kwarning', 'setcheckinterval', 'setdlopenflags', 'setprofile', 'setrecursionlimit', 'settrace', 'stderr', 'stdin', 'stdout', 'subversion', 'version', 'version_info', 'warnoptions']
如果要看里面下一级的属性stdout的属性：
>>> dir(sys.stdout)
['__class__', '__delattr__', '__doc__', '__enter__', '__exit__', '__format__', '__getattribute__', '__hash__', '__init__', '__iter__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'close', 'closed', 'encoding', 'errors', 'fileno', 'flush', 'isatty', 'mode', 'name', 'newlines', 'next', 'read', 'readinto', 'readline', 'readlines', 'seek', 'softspace', 'tell', 'truncate', 'write', 'writelines', 'xreadlines']
2、查看对象某个属性的帮助文档 ：如要查看sys的stdout属性，可以用__doc__， 使用方法为print(sys.stdout.__doc__)，如下图所示：
>>> print(sys.stdout.__doc__)
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.
3、查看对象的某个属性还可以用help函数，使用方法为help(sys.stdout)，如下图所示：
>>> help(sys.stdout)
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:
4、查看某个对象的详细文档用help
>>> help(sys)
Help on built-in module sys:


NAME
    sys


FILE
    (built-in)


MODULE DOCS
    />

DESCRIPTION
    This module provides access to some objects used or maintained by the
    interpreter and to functions that interact strongly with the interpreter.
    
    Dynamic objects:
    
    argv -- command line arguments; argv[0] is the script pathname if known
    path -- module search path; path[0] is the script directory, else ''
    modules -- dictionary of loaded modules