python中3个帮助函数help，di

>>> help("JSON")
Help on package json:

NAME
    json

FILE
    /usr/lib/python2.7/json/__init__.py

MODULE DOCS
    http://docs.Python.org/library/json

DESCRIPTION
    JSON (javascript Object Notation) <http://json.org> is a subset of
    JavaScript syntax (ECMA-262 3rd edition) used as a lightweight data
    interchange fORMat.
    
    :mod:`json` exposes an api familiar to users of the standard library
    :mod:`marshal` and :mod:`pickle` modules. It is the externally maintained
    version of the :mod:`json` library contained in Python 2.6, but maintains
    compatibility with Python 2.4 and Python 2.5 and (currently) has
    significant performance advantages, even without using the optional C
    extension for speedups.
    
    Encoding basic Python object hierarchies::

• 查看类

>>> help(json.JSONDecoder)
Help on class JSONDecoder in module json.decoder:

class JSONDecoder(__builtin__.object)
 |  Simple JSON <http://json.org> decoder
 |  
 |  Performs the following translations in decoding by default:
 |  
 |  +---------------+-------------------+
 |  | JSON          | Python            |
 |  +===============+===================+
 |  | object        | dict              |
 |  +---------------+-------------------+
 |  | array         | list              |
 |  +---------------+-------------------+
 |  | string        | unicode           |
 |  +---------------+-------------------+
 |  | number (int)  | int, long         |
 |  +---------------+-------------------+
 |  | number (real) | float             |
 |  +---------------+-------------------+
 |  | true          | True              |
 |  +---------------+-------------------+
 |  | false         | False             |

• 查看函数：

>>> help(json.dump)
Help on function dump in module json:

dump(obj, fp, skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, cls=None, indent=None, separators=None, encoding='utf-8', default=None, **kw)
    Serialize ``obj`` as a JSON formatted stream to ``fp`` (a
    ``.write()``-supporting file-like object).
    
    If ``skipkeys`` is true then ``dict`` keys that are not basic types
    (``str``, ``unicode``, ``int``, ``long``, ``float``, ``bool``, ``None``)
    will be skipped instead of raising a ``TypeError``.
    
    If ``ensure_ascii`` is false, then the some chunks written to ``fp``
    may be ``unicode`` instances, subject to normal Python ``str`` to
    ``unicode`` coercion rules. Unless ``fp.write()`` explicitly
    understands ``unicode`` (as in ``codecs.getwriter()``) this is likely
    to cause an error.

2 dir函数：查看变量可用的函数或方法

>>> import sys
>>> dir(sys)
['__displayhook__', '__doc__', '__excepthook__', '__name__', '__package__', '__stderr__', '__stdin__', '__stdout__', '_clear_type_cache', '_current_frames', '_getframe', '_mercurial', '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', 'exitfunc', 'flags', 'float_info', 'float_repr_style', 'getcheckinterval', 'getdefaultencoding', 'getdlopenflags', 'getfilesystemencoding', 'getprofile', 'getrecursionlimit', 'getrefcount', 'getsizeof', 'gettrace', 'hexversion', 'last_traceback', 'last_type', 'last_value', 'long_info', 'maxint', 'maxsize', 'maxunicode', 'meta_path', 'modules', 'path', 'path_hooks', 'path_importer_cache', 'platform', 'prefix', 'ps1', 'ps2', 'py3kwarning', 'pydebug', 'setcheckinterval', 'setdlopenflags', 'setprofile', 'setrecursionlimit', 'settrace', 'stderr', 'stdin', 'stdout', 'subversion', 'version', 'version_info', 'warnoptions']

3 type函数：查看变量的类型

<type 'module'>
>>> type (json.__name__)
<type 'str'>
>>> type (json.decoder)
<type 'module'>

4 退出python命令行

windows: ctrl+z 回车

linux：ctrl+d 

注：使用pydoc module 可查看模块的文档说明