python中3个帮助函数help，dir，type的使用

1 help函数：查看模块、函数、变量的详细说明：

查看模块

>>> help("modules")

Please wait a moment while I gather a list of all available modules...

BaseHTTPServer      array               htmllib             sets
Bastion             ast                 httplib             sgmllib
CDROM               asynchat            ihooks              sha
CGIHTTPServer       asyncore            imaplib             shelve
Canvas              atexit              imghdr              shlex
ConfigParser        audiodev            imp                 shutil
Cookie              audioop             importlib           signal
DLFCN               axi                 imputil             site
Dialog              base64              inspect             sitecustomize
DocXMLRPCServer     bdb                 io                  smtpd
FileDialog          binascii            itertools           smtplib

查看包

>>> 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