通过help()自学Python

摘要: 通过内置的help()、type()、dir()命令来自学Python中的类和方法。

pyhton中

通过如下链接学习相关基本内容，包括：基本数据类型、控制流、数据结构、模块、输入输出、异常捕获、类。

http://docs.python.org/2.7/tutorial/

1.help命令

help（类名）查看类中所有详细的功能
help（类名.函数名）查看类中某函数方法的详细内容

breath@ubuntu:~$ bpython
bpython version 0.15 on top of Python 2.7.6 /usr/bin/python2.7
>>> help
Type help() for interactive help, or help(object) for help about object.
>>> help()

Welcome to Python 2.7!  This is the online help utility.

If this is your first time using Python, you should definitely check out
the tutorial on the Internet at http://docs.python.org/2.7/tutorial/. 
Enter the name of any module, keyword, or topic to get help on writing
Python programs and using Python modules.  To quit this help utility and
return to the interpreter, just type "quit".

To get a list of available modules, keywords, or topics, type "modules",
"keywords", or "topics".  Each module also comes with a one-line summary
of what it does; to list the modules whose summaries contain a given word
such as "spam", type "modules spam".

help> q

You are now leaving help and returning to the Python interpreter.
If you want to ask for help on a particular object directly from the
interpreter, you can type "help(object)".  Executing "help('string')"
has the same effect as typing a particular string at the help> prompt.

>>> help(help)
Help on _Helper in module bpython.curtsiesfrontend._internal object:

class _Helper(bpython._internal._Helper)
|  Method resolution order:
|      _Helper
|      bpython._internal._Helper
|      __builtin__.object
|
|  Methods defined here:
|
|  __call__(self, *args, **kwargs)
|
|  __getattribute__(...)
|      x.__getattribu
3ff0
te__('name') <==> x.name
|
|  __init__(self, repl=None)
|
|  pager(self, output)
|
|  ----------------------------------------------------------------------
|  Methods inherited from bpython._internal._Helper:
|
|  __repr__(self)
|
|  ----------------------------------------------------------------------
|  Data descriptors inherited from bpython._internal._Helper:
|
|  __dict__
|      dictionary for instance variables (if defined)
|
|  __weakref__
|      list of weak references to the object (if defined)
~
~
~
~
~
~
~
~
~
~
~
(END)

2.The Python Standard Library

2.1__builtin__

备注：__builtin__模块中的objects（类对象）、functions（函数方法）、data（常量）、exception（异常）可以直接使用，无需import。除了__builtin__中显示的其它所有类，都需要通过import导入才能使用。

>>> help('__builtin__')
Help on built-in module __builtin__:

NAME
__builtin__ - Built-in functions, exceptions, and other objects.

FILE
(built-in)

DESCRIPTION
Noteworthy: None is the `nil' object; Ellipsis represents `...' in slices.

CLASSES
object
basestring
str
unicode
buffer
bytearray
classmethod
complex
dict
enumerate
file
float
frozenset
int
bool
list
long
memoryview
property
reversed
set
slice
staticmethod
super
tuple
type
xrange

class basestring(object)
|  Type basestring cannot be instantiated; it is the base for str and unicode.
|
...
...
...
FUNCTIONS
__import__(...)
__import__(name, globals={}, locals={}, fromlist=[], level=-1) -> module

Import a module. Because this function is meant for use by the Python
interpreter and not for general use it is better to use
importlib.import_module() to programmatically import a module.

The globals argument is only used to determine the context;
they are not modified.  The locals argument is unused.  The fromlist
should be a list of names to emulate ``from name import ...'', or an
empty list to emulate ``import name''.
When importing a module from a package, note that __import__('A.B', ...)
returns package A when fromlist is empty, but its submodule B when
fromlist is not empty.  Level is used to determine whether to perform
absolute or relative imports.  -1 is the original strategy of attempting
both absolute and relative imports, 0 is absolute, a positive number
is the number of parent directories to search relative to the current module.

abs(...)
abs(number) -> number

Return the absolute value of the argument.

all(...)
all(iterable) -> bool

Return True if bool(x) is True for all values x in the iterable.
If the iterable is empty, return True.

...
...
...
DATA
Ellipsis = Ellipsis
False = False
None = None
NotImplemented = NotImplemented
True = True
__debug__ = True
copyright = Copyright (c) 2001-2014 Python Software Foundati...ematisc...
credits =     Thanks to CWI, CNRI, BeOpen.com, Zope Corpor...opment.  ...
exit = Use exit() or Ctrl-D (i.e. EOF) to exit
help = Type help() for interactive help, or help(object) for help abou...
license = Type license() to see the full license text
quit = Use quit() or Ctrl-D (i.e. EOF) to exit

(END)

2.1.1查看类class

备注：查看类对象的时候会显示类的描述，类中的方法定义。

例子1：查看int类，以及类的__add__方法。

>>> help('int')

Help on class int in module __builtin__:

class int(object)
|  int(x=0) -> int or long
|  int(x, base=10) -> int or long
|
|  Convert a number or string to an integer, or return 0 if no arguments
|  are given.  If x is floating point, the conversion truncates towards zero.
|  If x is outside the integer range, the function returns a long instead.
|
|  If x is not a number or if base is given, then x must be a string or
|  Unicode object representing an integer literal in the given base.  The
|  literal can be preceded by '+' or '-' and be surrounded by whitespace.
|  The base defaults to 10.  Valid bases are 0 and 2-36.  Base 0 means to
|  interpret the base from the string as an integer literal.
|  >>> int('0b100', base=0)
|  4
|
|  Methods defined here:
|
|  __abs__(...)
|      x.__abs__() <==> abs(x)
|
|  __add__(...)
|      x.__add__(y) <==> x+y
...
...

>>> help('int.__add__')
Help on wrapper_descriptor in int:

int.__add__ = __add__(...)
x.__add__(y) <==> x+y

例子2：查看file类，以及类的close方法。

>>> help('file')
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.
...
...

>>> help('file.close')
Help on method_descriptor in file:

file.close = 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.

2.1.2查看声明statement

备注：声明包括：print、if、while、else、import、from、try、except、with、as等等。

>>> help('print')

The ``print`` statement
***********************

print_stmt ::= "print" ([expression ("," expression)* [","]]
| ">>" expression [("," expression)+ [","]])

...
...

2.2非__builtin__

备注：在标准库中，但是不在__builtin__模块中。安装python之后即存在的模块。不需要安装其它第三方模块即可使用。比如os模块。

>>> dir()
['__builtins__', '__doc__', '__name__', '__package__', 'help']
>>> import os
>>> dir()
['__builtins__', '__doc__', '__name__', '__package__', 'help', 'os']
>>> dir('os')
Help on module os:

NAME
os - OS routines for Mac, NT, or Posix depending on what system we're on.

FILE
/usr/lib/python2.7/os.py

MODULE DOCS http://docs.python.org/library/os 
DESCRIPTION
This exports:

...
...

3.type命令

备注：type命令可以查看对象的类型，

>>> help('type')

Help on class type in module __builtin__:

class type(object)
|  type(object) -> the object's type
|  type(name, bases, dict) -> a new type
|
...
...
>>> type(1)
<type 'int'>
>>> type('string')
<type 'str'>
>>> type([1])
<type 'list'>
>>> import os
>>> type(os)
<type 'module'>
>>> type(os.chown)
<type 'builtin_function_or_method'>

4.dir命令

备注：dir命令如果不加任何参数即：dir(),则显示当前作用域的所有names。

dir(模块)：则显示此模块的所有子模块和函数方法。

>>> help('dir')

Help on built-in function dir in module __builtin__:

dir(...)
dir([object]) -> list of strings

If called without an argument, return the names in the current scope.
Else, return an alphabetized list of names comprising (some of) the attributes
of the given object, and of attributes 
3ff0
;reachable from it.
If the object supplies a method named __dir__, it will be used; otherwise
the default dir() logic is used and returns:
for a module object: the module's attributes.
for a class object:  its attributes, and recursively the attributes
of its bases.
for any other object: its attributes, its class's attributes, and
recursively the attributes of its class's base classes.
(END)
>>> dir(os)
['EX_CANTCREAT', 'EX_CONFIG', 'EX_DATAERR', 'EX_IOERR', 'EX_NOHOST', 'EX_NOINPUT', 'EX_NOPERM', 'EX_NOUSER', 'EX_OK', 'EX_OSERR', 'EX_OSFILE', 'EX_PROTOC
OL', 'EX_SOFTWARE', 'EX_TEMPFAIL', 'EX_UNAVAILABLE', 'EX_USAGE', 'F_OK', 'NGROUPS_MAX', 'O_APPEND', 'O_ASYNC', 'O_CREAT', 'O_DIRECT', 'O_DIRECTORY', 'O_D
SYNC', 'O_EXCL', 'O_LARGEFILE', 'O_NDELAY', 'O_NOATIME', 'O_NOCTTY', 'O_NOFOLLOW', 'O_NONBLOCK', 'O_RDONLY', 'O_RDWR', 'O_RSYNC', 'O_SYNC', 'O_TRUNC', 'O
_WRONLY', 'P_NOWAIT', 'P_NOWAITO', 'P_WAIT', 'R_OK', 'SEEK_CUR', 'SEEK_END', 'SEEK_SET', 'ST_APPEND', 'ST_MANDLOCK', 'ST_NOATIME', 'ST_NODEV', 'ST_NODIRA
TIME', 'ST_NOEXEC', 'ST_NOSUID', 'ST_RDONLY', 'ST_RELATIME', 'ST_SYNCHRONOUS', 'ST_WRITE', 'TMP_MAX', 'UserDict', 'WCONTINUED', 'WCOREDUMP', 'WEXITSTATUS
', 'WIFCONTINUED', 'WIFEXITED', 'WIFSIGNALED', 'WIFSTOPPED', 'WNOHANG', 'WSTOPSIG', 'WTERMSIG', 'WUNTRACED', 'W_OK', 'X_OK', '_Environ', '__all__', '__bu
iltins__', '__doc__', '__file__', '__name__', '__package__', '_copy_reg', '_execvpe', '_exists', '_exit', '_get_exports_list', '_make_stat_result', '_mak
e_statvfs_result', '_pickle_stat_result', '_pickle_statvfs_result', '_spawnvef', 'abort', 'access', 'altsep', 'chdir', 'chmod', 'chown', 'chroot', 'close
', 'closerange', 'confstr', 'confstr_names', 'ctermid', 'curdir', 'defpath', 'devnull', 'dup', 'dup2', 'environ', 'errno', 'error', 'execl', 'execle', 'e
xeclp', 'execlpe', 'execv', 'execve', 'execvp', 'execvpe', 'extsep', 'fchdir', 'fchmod', 'fchown', 'fdatasync', 'fdopen', 'fork', 'forkpty', 'fpathconf',
'fstat', 'fstatvfs', 'fsync', 'ftruncate', 'getcwd', 'getcwdu', 'getegid', 'getenv', 'geteuid', 'getgid', 'getgroups', 'getloadavg', 'getlogin', 'getpgi
d', 'getpgrp', 'getpid', 'getppid', 'getresgid', 'getresuid', 'getsid', 'getuid', 'initgroups', 'isatty', 'kill', 'killpg', 'lchown', 'linesep', 'link',
'listdir', 'lseek', 'lstat', 'major', 'makedev', 'makedirs', 'minor', 'mkdir', 'mkfifo', 'mknod', 'name', 'nice', 'open', 'openpty', 'pardir', 'path', 'p
athconf', 'pathconf_names', 'pathsep', 'pipe', 'popen', 'popen2', 'popen3', 'popen4', 'putenv', 'read', 'readlink', 'remove', 'removedirs', 'rename', 're
names', 'rmdir', 'sep', 'setegid', 'seteuid', 'setgid', 'setgroups', 'setpgid', 'setpgrp', 'setregid', 'setresgid', 'setresuid', 'setreuid', 'setsid', 's
etuid', 'spawnl', 'spawnle', 'spawnlp', 'spawnlpe', 'spawnv', 'spawnve', 'spawnvp', 'spawnvpe', 'stat', 'stat_float_times', 'stat_result', 'statvfs', 'st
atvfs_result', 'strerror', 'symlink', 'sys', 'sysconf', 'sysconf_names', 'system', 'tcgetpgrp', 'tcsetpgrp', 'tempnam', 'times', 'tmpfile', 'tmpnam', 'tt
yname', 'umask', 'uname', 'unlink', 'unsetenv', 'urandom', 'utime', 'wait', 'wait3', 'wait4', 'waitpid', 'walk', 'write']
>>>