Lesson 8
课程介绍的python内容毕竟有限，所以在自学过程中你可能需要得到及时的帮助，使得自己对所要使用的方法有所了解。因此，你可以了解一下python的interactive help，学会使用它可以帮助你自学的时候获取class，function和module的信息。
Help
# To begin
dir() # short for "directory"
['In',
'Out',
'_',
'__',
'___',
'__builtin__',
'__builtins__',
'__doc__',
'__loader__',
'__name__',
'__package__',
'__spec__',
'_dh',
'_i',
'_i1',
'_ih',
'_ii',
'_iii',
'_oh',
'_sh',
'exit',
'get_ipython',
'quit']
显示的是目前可以调用的内建对象。本节课以’ builtins ‘模块为例，讲述如何获得帮助。对于内建对象还不了解的同学，可以看http://blog.51cto.com/xpleaf/1764849 一文中的解释。
# get the functions in '__builtins__'
dir(__builtins__)
['ArithmeticError',
'AssertionError',
'AttributeError',
'BaseException',
'BlockingIOError',
'BrokenPipeError',
'BufferError',
'BytesWarning',
'ChildProcessError',
'ConnectionAbortedError',
'ConnectionError',
'ConnectionRefusedError',
'ConnectionResetError',
'DeprecationWarning',
'EOFError',
'Ellipsis',
'EnvironmentError',
'Exception',
'False',
'FileExistsError',
'FileNotFoundError',
'FloatingPointError',
'FutureWarning',
'GeneratorExit',
'IOError',
'ImportError',
'ImportWarning',
'IndentationError',
'IndexError',
'InterruptedError',
'IsADirectoryError',
'KeyError',
'KeyboardInterrupt',
'LookupError',
'MemoryError',
'ModuleNotFoundError',
'NameError',
'None',
'NotADirectoryError',
'NotImplemented',
'NotImplementedError',
'OSError',
'OverflowError',
'PendingDeprecationWarning',
'PermissionError',
'ProcessLookupError',
'RecursionError',
'ReferenceError',
'ResourceWarning',
'RuntimeError',
'RuntimeWarning',
'StopAsyncIteration',
'StopIteration',
'SyntaxError',
'SyntaxWarning',
'SystemError',
'SystemExit',
'TabError',
'TimeoutError',
'True',
'TypeError',
'UnboundLocalError',
'UnicodeDecodeError',
'UnicodeEncodeError',
'UnicodeError',
'UnicodeTranslateError',
'UnicodeWarning',
'UserWarning',
'ValueError',
'Warning',
'ZeroDivisionError',
'__IPYTHON__',
'__build_class__',
'__debug__',
'__doc__',
'__import__',
'__loader__',
'__name__',
'__package__',
'__spec__',
'abs',
'all',
'any',
'ascii',
'bin',
'bool',
'bytearray',
'bytes',
'callable',
'chr',
'classmethod',
'compile',
'complex',
'copyright',
'credits',
'delattr',
'dict',
'dir',
'display',
'divmod',
'dreload',
'enumerate',
'eval',
'exec',
'filter',
'float',
'format',
'frozenset',
'get_ipython',
'getattr',
'globals',
'hasattr',
'hash',
'help',
'hex',
'id',
'input',
'int',
'isinstance',
'issubclass',
'iter',
'len',
'license',
'list',
'locals',
'map',
'max',
'memoryview',
'min',
'next',
'object',
'oct',
'open',
'ord',
'pow',
'print',
'property',
'range',
'repr',
'reversed',
'round',
'set',
'setattr',
'slice',
'sorted',
'staticmethod',
'str',
'sum',
'super',
'tuple',
'type',
'vars',
'zip']
打印出来的是该模块所有可以调用的函数，下面举个例子看看：
# for example, let's learn about 'pow' function
help(pow)
Help on built-in function pow in module builtins:
pow(x, y, z=None, /)
Equivalent to x**y (with two arguments) or x**y % z
(with three arguments)
Some types, such as ints, are able to use a more efficient algorithm
when invoked using the three argument form.
利用help()可以得到模块中函数的解释：
- 第一行，表示该函数在 builtins 模块中；
- 下面的部分，是解释如何使用这个函数。
在pow()函数中有三个参数，x，y，z。最终的输出为ints类型的number。
[一般包括参数、功能介绍、输入输出和详细信息。]
pow(2,10)
1024
# of course, you can also get the result by using another way in the description
2 ** 10
1024
下面我们再举个例子：hex()
help(hex)
Help on built-in function hex in module builtins:
hex(number, /)
Return the hexadecimal representation of an integer.
>>> hex(12648430)
'0xc0ffee'
hex的功能就不赘述了，给定一个int类型数，返回其十六进制的转换，以string类型给出。不过，这里又一个小注意点，python自带对十六进制的解释：
hex(10)
'0xa'
0xa
10
List of modules
help('modules')
Please wait a moment while I gather a list of all available modules...
/usr/local/lib/python3.6/dist-packages/IPython/kernel/__init__.py:13: ShimWarning: The `IPython.kernel` package has been deprecated since IPython 4.0.You should import from ipykernel or jupyter_client instead.
"You should import from ipykernel or jupyter_client instead.", ShimWarning)
Using TensorFlow backend.
/usr/local/lib/python3.6/dist-packages/nltk/twitter/__init__.py:20: UserWarning: The twython library has not been installed. Some functionality from the twitter package will not be available.
warnings.warn("The twython library has not been installed. "
/usr/local/lib/python3.6/dist-packages/IPython/utils/traitlets.py:5: UserWarning:
IPython.utils.traitlets has moved to a top-level traitlets package.
<IPython.core.display.Javascript object>
/usr/local/lib/python3.6/dist-packages/skimage/viewer/__init__.py:6: UserWarning:
Viewer requires Qt
/usr/local/lib/python3.6/dist-packages/statsmodels/compat/pandas.py:56: FutureWarning:
The pandas.core.datetools module is deprecated and will be removed in a future version. Please use the pandas.tseries module instead.
/usr/lib/python3.6/pkgutil.py:107: VisibleDeprecationWarning:
zmq.eventloop.minitornado is deprecated in pyzmq 14.0 and will be removed.
Install tornado itself to use zmq with the tornado IOLoop.
IPython bz2 lsb_release selectors
PIL cProfile lzma setuptools
__future__ cachetools macpath shelve
_ast calendar macurl2path shlex
_asyncio certifi mailbox shutil
_bisect cgi mailcap signal
_blake2 cgitb markdown simplegeneric
_bootlocale chardet markupsafe site
_bz2 chunk marshal sitecustomize
_codecs cmath math six
_codecs_cn cmd matplotlib skimage
_codecs_hk code mimetypes sklearn
_codecs_iso2022 codecs mistune smtpd
_codecs_jp codeop mmap smtplib
_codecs_kr collections modulefinder sndhdr
_codecs_tw colorsys mpmath socket
_collections compileall msgpack socketserver
_collections_abc concurrent msgpack_numpy softwareproperties
_compat_pickle configparser multiprocessing spacy
_compression contextlib murmurhash spwd
_crypt copy nbconvert sqlite3
_csv copyreg nbformat sre_compile
_ctypes crcmod netrc sre_constants
_ctypes_test crypt networkx sre_parse
_curses csv nis ssl
_curses_panel ctypes nltk stat
_datetime curses nntplib statistics
_dbm cv2 notebook statsmodels
_dbus_bindings cycler ntpath storemagic
_dbus_glib_bindings cymem nturl2path string
_decimal cythonmagic numbers stringprep
_dummy_thread cytoolz numpy struct
_elementtree datetime oauth2client subprocess
_functools dateutil oauthlib sunau
_hashlib dbm olefile symbol
_heapq dbus opcode sympy
_imp decimal operator sympyprinting
_io decorator optparse symtable
_json defusedxml os sys
_locale difflib ossaudiodev sysconfig
_lsprof dill pandas syslog
_lzma dis pandas_gbq tabnanny
_markupbase distutils pandocfilters tarfile
_md5 doctest parser telnetlib
_multibytecodec dummy_threading past tempfile
_multiprocessing easy_install pathlib tensorboard
_opcode email patsy tensorflow
_operator encodings pdb tensorflow_hub
_osx_support entrypoints pexpect termcolor
_pickle enum pickle terminado
_posixsubprocess errno pickleshare termios
_pydecimal faulthandler pickletools test
_pyio fcntl pip test_regex
_random filecmp pipes testpath
_regex fileinput pkg_resources tests
_regex_core filelock pkgutil textwrap
_sha1 fnmatch plac theano
_sha256 formatter plac_core thinc
_sha3 fractions plac_ext this
_sha512 ftplib plac_tk threading
_signal functools platform time
_sitebuiltins future plistlib timeit
_socket gast plotly tkinter
_sqlite3 gc pluggy tlz
_sre genericpath poplib token
_ssl getopt portpicker tokenize
_stat getpass posix toml
_string gettext posixpath toolz
_strptime gi pprint tornado
_struct glob preshed tqdm
_symtable google_auth_httplib2 profile trace
_sysconfigdata_m_linux_x86_64-linux-gnu google_auth_oauthlib prompt_toolkit traceback
_testbuffer googleapiclient pstats tracemalloc
_testcapi grp psutil traitlets
_testimportmultiple grpc pty tty
_testmultiphase gzip ptyprocess turtle
_thread h5py pwd types
_threading_local hashlib py typing
_tkinter heapq py_compile ujson
_tracemalloc hmac pyasn1 unicodedata
_warnings html pyasn1_modules unittest
_weakref http pyclbr uritemplate
_weakrefset httplib2 pydoc urllib
abc idna pydoc_data urllib3
absl imaplib pyexpat uu
aifc imghdr pygments uuid
altair imp pygtkcompat vega_datasets
antigravity importlib pylab venv
apiclient inspect pymc3 virtualenv
apt io pyparsing virtualenv_support
apt_inst ipaddress pystache warnings
apt_pkg ipykernel pytz wave
aptsources ipykernel_launcher pywt wcwidth
argparse ipython_genutils queue weakref
array itertools quopri webbrowser
ast jinja2 random webencodings
astor joblib re werkzeug
asynchat json readline wheel
asyncio jsonschema regex wrapt
asyncore jupyter reprlib wsgiref
atexit jupyter_client requests xdrlib
audioop jupyter_core requests_oauthlib xgboost
autoreload keras resource xml
base64 keras_applications rlcompleter xmlrpc
bdb keras_preprocessing rmagic xxlimited
bin keyword rsa xxsubtype
binascii lib2to3 runpy yaml
binhex libfuturize sched zipapp
bisect libpasteurize scipy zipfile
bleach linecache seaborn zipimport
bs4 locale secrets zlib
builtins logging select zmq
Enter any module name to get more help. Or, type "modules spam" to search
for modules whose name or summary contain the string "spam".
此处列出的是可以调用的模块，比如要是装了numpy或者什么的，就会在这个list中。下面讲讲怎么去直接获取这些模块里的帮助信息。
# eg: math
# step 1: import
import math
# check
dir()
['In',
'Out',
'_',
'_1',
'_2',
'_4',
'_5',
'_7',
'_8',
'__',
'___',
'__builtin__',
'__builtins__',
'__doc__',
'__loader__',
'__name__',
'__package__',
'__spec__',
'_dh',
'_i',
'_i1',
'_i10',
'_i11',
'_i2',
'_i3',
'_i4',
'_i5',
'_i6',
'_i7',
'_i8',
'_i9',
'_ih',
'_ii',
'_iii',
'_oh',
'_sh',
'exit',
'get_ipython',
'math',
'quit']
此时，math模块就加入到你的内建list，代表你可以调用它了。
dir(math)
['__doc__',
'__loader__',
'__name__',
'__package__',
'__spec__',
'acos',
'acosh',
'asin',
'asinh',
'atan',
'atan2',
'atanh',
'ceil',
'copysign',
'cos',
'cosh',
'degrees',
'e',
'erf',
'erfc',
'exp',
'expm1',
'fabs',
'factorial',
'floor',
'fmod',
'frexp',
'fsum',
'gamma',
'gcd',
'hypot',
'inf',
'isclose',
'isfinite',
'isinf',
'isnan',
'ldexp',
'lgamma',
'log',
'log10',
'log1p',
'log2',
'modf',
'nan',
'pi',
'pow',
'radians',
'sin',
'sinh',
'sqrt',
'tan',
'tanh',
'tau',
'trunc']
# radians
help(radians) # return the NameError
---------------------------------------------------------------------------
NameError Traceback (most recent call last)
<ipython-input-13-8223eb0f88be> in <module>()
----> 1 help(radians)
NameError: name 'radians' is not defined
# This is because that it is not the inner module in python
# You must use in this way
help(math.radians)
Help on built-in function radians in module math:
radians(...)
radians(x)
Convert angle x from degrees to radians.
从描述中可以得到，radians函数可以将给定的角度转换成π。
radians(180) # return the NameError again
---------------------------------------------------------------------------
NameError Traceback (most recent call last)
<ipython-input-15-165408e9dc79> in <module>()
----> 1 radians(180)
NameError: name 'radians' is not defined
math.radians(180)
3.141592653589793
因此，一定要记住，如果不是python内建模块，在调用模块函数时，前面一定要把模块名一起写在来。
Youtube source:
https://www.youtube.com/watch?v=bY6m6_IIN94&list=PLi01XoE8jYohWFPpC17Z-wWhPOSuh8Er-