In : from pathlib import Path
In : Path.home()
Out: PosixPath('/Users/dongweiming')  # 用户目录
In : path = Path('/user')
In : path / 'local'  # 非常直观
Out: PosixPath('/user/local')
In : str(path / 'local' / 'bin')
Out: '/user/local/bin'

In : f = Path('example.txt')
In : f.write_bytes('This is the content'.encode('utf-8'))
Out[16]: 19

In : with f.open('r', encoding='utf-8') as handle:  # open现在是方法了
....:         print('read from open(): {!r}'.format(handle.read()))
....:
read from open(): 'This is the content'

In : p = Path('touched')
In : p.exists()  # 集成了多个常用方法
Out: False
In : p.touch()
In : p.exists()
Out: True

In : p.with_suffix('.jpg')
Out: PosixPath('touched.jpg')
In : p.is_dir()
Out: False
In : p.joinpath('a', 'b')
Out: PosixPath('touched/a/b')

In : a, b, *rest = range(10)  # 学过lisp就很好懂了，相当于一个「everything else」
In : a
Out: 0
In : b
Out: 1
In : rest
Out: [2, 3, 4, 5, 6, 7, 8, 9]

In : *prev, next_to_last, last = range(10)
In : prev, next_to_last, last
Out: ([0, 1, 2, 3, 4, 5, 6, 7], 8, 9)

In : def recv(maxsize, *, block):
....:
....:     pass
....:

In : recv(1024, True)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-49-8e61db2ef94b> in <module>()
----> 1 recv(1024, True)

TypeError: recv() takes 1 positional argument but 2 were given

In : recv(1024, block=True)

found_images = \
    glob.glob('/path/*.jpg') \
  + glob.glob('/path/*/*.jpg') \
  + glob.glob('/path/*/*/*.jpg') \
  + glob.glob('/path/*/*/*/*.jpg') \
  + glob.glob('/path/*/*/*/*/*.jpg')

found_images = glob.glob('/path/**/*.jpg', recursive=True)

found_images = pathlib.Path('/path/').glob('**/*.jpg')

In : print(*[1, 2, 3], sep='\t')
1   2   3
In : [x if x % 3 else print('', x) for x in range(10)]
 0
 3
 6
 9
Out: [None, 1, 2, None, 4, 5, None, 7, 8, None]

In : name = 'Fred'
In : f'My name is {name}'
Out: 'My name is Fred'

In : from datetime import *
In : date = datetime.now().date()
In : f'{date} was on a {date:%A}'
Out: '2018-01-17 was on a Wednesday'

In : def foo():
....:     return 20
....:
In : f'result={foo()}'
Out: 'result=20'

3 < '3'
2 < None
(3, 4) < (3, None)
(4, 5) < [4, 5]
sorted([2, '1', 3])

In : s = '您好'

In : print(len(s))
6

In : print(s[:2])
?

In : s = '您好'

In : print(len(s))
2

In : print(s[:2])
您好

In : x = dict(a=1, b=2)
In : y = dict(b=3, d=4)
In : z = {**x, **y}
In : z
Out: {'a': 1, 'b': 3, 'd': 4}

In : {str(i):i for i in range(5)}
Out: {'0': 0, '1': 1, '2': 2, '3': 3, '4': 4}

❯ brew install python3  # 如果已经安装了可以忽略
❯ python3 -m pip install --upgrade --force-reinstall pip
❯ pip3 install pipenv --user  # 推荐安装在个人目录下
❯ export PATH="/Users/dongweiming/Library/Python/3.6/bin:$PATH"  # 把用户目录下bin放在最前面，这样可以直接使用pipenv了

❯ mkdir test_pipenv
❯ cd test_pipenv
❯ pipenv install  # 创建一个虚拟环境
Creating a virtualenv for this project…
...
Installing setuptools, pip, wheel...done.

Virtualenv location: /Users/dongweiming/.virtualenvs/test_pipenv-GP_s2TW5
Creating a Pipfile for this project…
Pipfile.lock not found, creating…
Locking [dev-packages] dependencies…
Locking [packages] dependencies…
Updated Pipfile.lock (c23e27)!
Installing dependencies from Pipfile.lock (c23e27)…
  🐍   ▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉ 0/0 — 00:00:00
To activate this project's virtualenv, run the following:
 $ pipenv shell

❯ which python3
/usr/local/Cellar/python3/3.6.1/bin/python3  # 还是mac自带的Python

❯ pipenv shell  # 激活虚拟环境
Spawning environment shell (/bin/zsh). Use 'exit' to leave.
source /Users/dongweiming/.virtualenvs/test_pipenv-GP_s2TW5/bin/activate

❯ which python3  # 已经在虚拟环境里了
/Users/dongweiming/.virtualenvs/test_pipenv-GP_s2TW5/bin/python3

❯ exit  # 退出虚拟环境

❯ which python3
/usr/local/Cellar/python3/3.6.1/bin/python3

❯ ls
Pipfile  Pipfile.lock

❯ pipenv install elasticsearch-dsl requests
Installing elasticsearch-dsl…
...
Adding elasticsearch-dsl to Pipfile's [packages]…
Installing requests…
...
Adding requests to Pipfile's [packages]…
  PS: You have excellent taste! ✨ 🍰 ✨
Locking [dev-packages] dependencies…
Locking [packages] dependencies…
Updated Pipfile.lock (8d307d)!

❯ pipenv graph
elasticsearch-dsl==6.1.0
  - elasticsearch [required: <7.0.0,>=6.0.0, installed: 6.1.1]
    - urllib3 [required: <1.23,>=1.21.1, installed: 1.22]
  - ipaddress [required: Any, installed: 1.0.19]
  - python-dateutil [required: Any, installed: 2.6.1]
    - six [required: >=1.5, installed: 1.10.0]
  - six [required: Any, installed: 1.10.0]
requests==2.18.4
  - certifi [required: >=2017.4.17, installed: 2017.11.5]
  - chardet [required: <3.1.0,>=3.0.2, installed: 3.0.4]
  - idna [required: <2.7,>=2.5, installed: 2.6]
  - urllib3 [required: <1.23,>=1.21.1, installed: 1.22]

❯ pipenv uninstall `pipenv graph --json |python3 depends.py requests`
Un-installing certifi…
Uninstalling certifi-2017.11.5:
  Successfully uninstalled certifi-2017.11.5

No package certifi to remove from Pipfile.
Un-installing requests…
Uninstalling requests-2.18.4:
  Successfully uninstalled requests-2.18.4

Removing requests from Pipfile…
Un-installing idna…
Uninstalling idna-2.6:
  Successfully uninstalled idna-2.6

No package idna to remove from Pipfile.
Un-installing chardet…
Uninstalling chardet-3.0.4:
  Successfully uninstalled chardet-3.0.4

No package chardet to remove from Pipfile.
Locking [dev-packages] dependencies…
Locking [packages] dependencies…
Updated Pipfile.lock (c05ac4)!

❯ cat depends.py
import sys
import json

package = sys.argv[1]
other_dependencies = set()
removing_dependencies = set([package])

for i in json.load(sys.stdin):
    for p in i['dependencies']:
        key = p['key']
        if i['package']['key'] == package:
            removing_dependencies.add(key)
        else:
            other_dependencies.add(key)

print(' '.join(removing_dependencies - other_dependencies))

❯ pipenv graph
elasticsearch-dsl==6.1.0
  - elasticsearch [required: >=6.0.0,<7.0.0, installed: 6.1.1]
    - urllib3 [required: >=1.21.1,<1.23, installed: 1.22]
  - ipaddress [required: Any, installed: 1.0.19]
  - python-dateutil [required: Any, installed: 2.6.1]
    - six [required: >=1.5, installed: 1.10.0]
  - six [required: Any, installed: 1.10.0]

❯ pipenv run which python # 「pipenv run」可以激活虚拟环境，并使用shell命令
/Users/dongweiming/.virtualenvs/test_pipenv-GP_s2TW5/bin/python
❯ pipenv check  # 检查装的包的安全性
Checking PEP 508 requirements…
Passed!
Checking installed package safety…
All good!
❯ pipenv --man  # 传统的看文档的方法
❯ pipenv check --style depends.py  # 代码Flake8检查，在这里我修改了depends.py让它故意有问题
/Users/dongweiming/test_pipenv/depends.py:1:1: F401 'os' imported but unused

In : class ObjectCreator(object):
...:     pass
...:

In : my_object = ObjectCreator()

In : my_object
Out: <__main__.ObjectCreator at 0x1082bbef0>

In : print(ObjectCreator)
<class '__main__.ObjectCreator'>

In : def func(instance):
...:     print(instance.a, instance.b)
...:     print(instance.method_a(10))
...:

In : def generate_cls(a, b):
...:     class Fake(object):
...:         def method_a(self, n):
...:             return n
...:     Fake.a = a
...:     Fake.b = b
...:     return Fake
...:

In : ins = generate_cls(1, 2)()

In : ins.a, ins.b, ins.method_a(10)
Out: (1, 2, 10)

In : def method_a(self, n):
...:     return n
...: 
In : ins = type('Fake', (), {'a': 1, 'b': 2, 'method_a': method_a})()

In : ins.a, ins.b, ins.method_a(10)
Out: (1, 2, 10)

In : type(1)
Out: int

In : type('1')
Out: str

In : type(ObjectCreator)
Out: type

In : type(ObjectCreator())
Out: __main__.ObjectCreator

MyClass = type('MyClass', (), {})

In : age = 35
In : age.__class__
Out: int

In : name = 'bob'
In : name.__class__
Out: str
...

In : age.__class__.__class__
Out: type

In : name.__class__.__class__
Out: type
...

class Foo(object):
    __metaclass__ = something...
    [...]

class Simple1(object, metaclass=something...):
    [...]

class HelloMeta(type):
    def __new__(cls, name, bases, attrs):
        def __init__(self, func):
            self.func = func
        def hello(self):
            print 'hello world'
        t = type.__new__(cls, name, bases, attrs)
        t.__init__ = __init__
        t.hello = hello
        return t

class New_Hello(object):
    __metaclass__ = HelloMeta

In : h = New_Hello(lambda x: x)

In : h.func(10), h.hello()
hello world
Out: (10, None)

In : class HelloMeta2(type):
...:     def __init__(cls, name, bases, attrs):
...:         super(HelloMeta2, cls).__init__(name, bases, attrs)
...:         attrs_ = {}
...:         for k, v in attrs.items():
...:             if not k.startswith('__'):
...:                 attrs_[k] = v
...:         setattr(cls, '_new_dict', attrs_)
...:
...:

In : class New_Hello2(metaclass=HelloMeta2):
...:     a = 1
...:     b = True

In : New_Hello2._new_dict
Out: {'a': 1, 'b': True}

In : h2 = New_Hello2()

In : h2._new_dict
Out: {'a': 1, 'b': True}

-   repo: https://github.com/pre-commit/pre-commit-hooks
    sha: b03733bc86d9e8b2564a5798ade40d64baae3055
    hooks:
    -   id: trailing-whitespace
    -   id: end-of-file-fixer
    -   id: autopep8-wrapper
    args: ['-i', '--ignore=E265,E309,E501']
    -   id: check-docstring-first
    -   id: check-json
    -   id: check-yaml
    -   id: debug-statements
    -   id: name-tests-test
    -   id: requirements-txt-fixer
    -   id: flake8
-   repo: https://github.com/pre-commit/pre-commit
    sha: 86c99c6b870a261d2aff0b4cdb36995764edce1b
    hooks:
    -   id: validate_config
    -   id: validate_manifest
-   repo: https://github.com/asottile/reorder_python_imports
    sha: ea9fa14a757bb210d849de5af8f8ba2c9744027a
    hooks:
    -   id: reorder-python-imports

pip install pre-commit
pre-commit install
# PS: 第一次执行commit会比较慢，因为他会clone对应的源, 之后就会用这个缓存的源
# 其他的可选源和用法直接参照[https://github.com/pre-commit](https://github.com/pre-commit)里面的项目或者[http://pre-commit.com/hooks.html](http://pre-commit.com/hooks.html)

$git commit -m 'test'

Trim Trailing Whitespace.................................................................................................................Passed
Fix End of Files.........................................................................................................................Passed
autopep8 wrapper.........................................................................................................................Passed
Check docstring is first.................................................................................................................Passed
Check JSON..........................................................................................................(no files to check) Skipped
Check Yaml..........................................................................................................(no files to check) Skipped
Debug Statements (Python)................................................................................................................Passed
Tests should end in _test.py........................................................................................(no files to check) Skipped
Fix requirements.txt................................................................................................(no files to check) Skipped
Flake8...................................................................................................................................Failed
hookid: flake8

pre_commit/__init__.py:2:1: F401 'os' imported but unused
pre_commit/__init__.py:3:1: F401 'sys' imported but unused

Validate Pre-Commit Config..........................................................................................(no files to check) Skipped
Validate Pre-Commit Manifest........................................................................................(no files to check) Skipped
Reorder python imports...................................................................................................................Passed
# 因为我的flake8有问题 所以commit失败了

pre-commit install -t pre-commit # 默认安装pre-commit钩子, 每次commit触发
pre-commit install -t pre-push # 默认安装pre-push钩子, 每次push触发

%lsmagic

import os.path
from functools import wraps
from operator import attrgetter
from urlparse import urlparse

from db import DB # db.py提供的接口
from IPython.core.magic import Magics, magics_class, line_magic # 这三个就是我们需要做magic插件的组件


def get_or_none(attr):
    return attr if attr else None


def check_db(func):
    @wraps(func)
    def deco(*args):
        if args[0]._db is None: # 每个magic都需要首页实例化过db，so 直接加装饰器来判断
            print '[ERROR]Please make connection: `con = %db_connect xx` or `%use_credentials xx` first!'  # noqa
            return
        return func(*args)
    return deco


@magics_class  # 每个magic都需要加这个magics_class装饰器
class SQLDB(Magics): # 要继承至Magics
    _db = None # 每次打开ipython都是一次实例化

    @line_magic('db_connect') # 这里用了line_magic 表示它是一个line magic.(其他2种一会再说) magic的名字是db_connect. 注意 函数名不重要
                              # 最后我们用 %db_connect而不是%conn
    def conn(self, parameter_s): # 每个这样的方法都接收一个参数 就是你在ipython里输入的内容
        """Conenct to database in ipython shell.
        Examples::
            %db_connect
            %db_connect postgresql://user:pass@localhost:port/database
        """
        uri = urlparse(parameter_s) # 剩下的都是解析parameter_s的逻辑

        if not uri.scheme:
            params = {
                'dbtype': 'sqlite',
                'filename': os.path.join(os.path.expanduser('~'), 'db.sqlite')
            }
        elif uri.scheme == 'sqlite':
            params = {
                'dbtype': 'sqlite',
                'filename': uri.path
            }
        else:
            params = {
                'username': get_or_none(uri.username),
                'password': get_or_none(uri.password),
                'hostname': get_or_none(uri.hostname),
                'port': get_or_none(uri.port),
                'dbname': get_or_none(uri.path[1:])
            }

        self._db = DB(**params) # 这里给_db赋值

        return self._db # return的结果就会被ipython接收,显示出来

    @line_magic('db') # 一个新的magic 叫做%db -- 谨防取名冲突
    def db(self, parameter_s):
        return self._db

    @line_magic('table')
    @check_db
    def table(self, parameter_s):
        p = parameter_s.split() # 可能传进来的是多个参数,但是对ipython来说,传进来的就是一堆字符串，所以需要按空格分隔下
        l = len(p)
        if l == 1:
            if not p[0]:
                return self._db.tables
            else:
                return attrgetter(p[0])(self._db.tables)
        else:
            data = self._db.tables
            for c in p:
                if c in ['head', 'sample', 'unique', 'count', 'all', 'query']:
                    data = attrgetter(c)(data)()
                else:
                    data = attrgetter(c)(data)
            return data

def load_ipython_extension(ipython): # 注册一下. 假如你直接去ipython里面加 就不需要这个了
    ipython.register_magics(SQLDB)

In [1]: !ruby -e 'p "hello"'
"hello"

In [2]: %%ruby # 也可以这样
   ...: p "hello"
      ...:
      "hello"

再说个notebook的:

In [3]: %%javascript
   ...: require.config({
   ...:     paths: {
   ...:         chartjs: '//code.highcharts.com/highcharts'
   ...:     }
   ...: });
   ...:
   <IPython.core.display.Javascript object>
});

In [4]: %time 2**128
CPU times: user 2 µs, sys: 1 µs, total: 3 µs
Wall time: 5.01 µs
Out[4]: 340282366920938463463374607431768211456L

In [5]: %%time
   ...: 2**128
   ...:
   CPU times: user 4 µs, sys: 0 ns, total: 4 µs
   Wall time: 9.06 µs
   Out[5]: 340282366920938463463374607431768211456L

@line_cell_magic
def xx(self, line='', cell=None):

@line_cell_magic
def prun(self, parameter_s='', cell=None):
    opts, arg_str = self.parse_options(parameter_s, 'D:l:rs:T:q',
                                       list_all=True, posix=False)
    ...

@magic_arguments.magic_arguments() # 最上面
@magic_arguments.argument('--breakpoint', '-b', metavar='FILE:LINE',
    help="""
    Set break point at LINE in FILE.
    """
) # 这种argument可以有多个
@magic_arguments.argument('statement', nargs='*',
    help="""
    Code to run in debugger.
    You can omit this in cell magic mode.
    """
)
@line_cell_magic
def debug(self, line='', cell=None):
    args = magic_arguments.parse_argstring(self.debug, line) # 要保持第一个参数等于这个方法名字,这里就是self.debug
    ...

In [1]: def append_to_list(value, def_list=[]):
   ...:         def_list.append(value)
   ...:         return def_list
   ...: 

In [2]: my_list = append_to_list(1)

In [3]: my_list
Out[3]: [1]

In [4]: my_other_list = append_to_list(2)

In [5]: my_other_list
Out[5]: [1, 2] # 看到了吧，其实我们本来只想生成[2] 但是却把第一次运行的效果页带了进来

In [6]: import time

In [7]: def report_arg(my_default=time.time()):
   ...:         print(my_default)
   ...:     

In [8]: report_arg() # 第一次执行
1399562371.32

In [9]: time.sleep(2) # 隔了2秒

In [10]: report_arg()
1399562371.32 # 时间竟然没有变

def append_to_list(element, to=None):
    if to is None:
        to = []
    to.append(element)
    return to

In [12]: gen = (i for i in range(5))

In [13]: 2 in gen
Out[13]: True

In [14]: 3 in gen
Out[14]: True

In [15]: 1 in gen
Out[15]: False # 1为什么不在gen里面了? 因为调用1->2,这个时候1已经不在迭代器里面了,被按需生成过了

In [20]: gen = (i for i in range(5))

In [21]: a_list = list(gen) # 可以转化成列表，当然a_tuple = tuple(gen) 也可以

In [22]: 2 in a_list
Out[22]: True

In [23]: 3 in a_list
Out[23]: True

In [24]: 1 in a_list # 就算循环过,值还在
Out[24]: True

In [29]: my_list = [lambda: i for i in range(5)]

In [30]: for l in my_list:
   ....:         print(l())
   ....:     
4
4
4
4
4

In [31]: my_gen = (lambda: n for n in range(5))

In [32]: for l in my_gen:
   ....:         print(l())
   ....:     
0
1
2
3
4

In [33]: my_list = [lambda x=i: x for i in range(5)] # 看我给每个lambda表达式赋了默认值

In [34]: for l in my_list:
   ....:         print(l())
   ....:     
0
1
2
3
4

In [35]: def groupby(items, size):
   ....:     return zip(*[iter(items)]*size)
   ....: 

In [36]: groupby(range(9), 3)
Out[36]: [(0, 1, 2), (3, 4, 5), (6, 7, 8)]

In [39]: [iter(items)]*3
Out[39]: 
[<listiterator at 0x10e155fd0>,
 <listiterator at 0x10e155fd0>,
 <listiterator at 0x10e155fd0>] # 看到了吧, 其实就是把items变成可迭代的, 重复三回（同一个对象哦）, 但是别忘了,每次都.next(), 所以起到了分组的作用
 In [40]: [lambda x=i: x for i in range(5)]
Out[40]: 
[<function __main__.<lambda>>,
 <function __main__.<lambda>>,
 <function __main__.<lambda>>,
 <function __main__.<lambda>>,
 <function __main__.<lambda>>] # 看懂了吗?

In [44]: a = [1, 2, 3, 4, 5]

In [45]: for i in a:
   ....:     if not i % 2:
   ....:         a.remove(i)
   ....:         

In [46]: a
Out[46]: [1, 3, 5] # 没有问题

In [50]: b = [2, 4, 5, 6]

In [51]: for i in b:
   ....:      if not i % 2:
   ....:          b.remove(i)
   ....:         

In [52]: b
Out[52]: [4, 5] # 本来我想要的结果应该是去除偶数的列表

In [53]: b = [2, 4, 5, 6]

In [54]: for index, item in enumerate(b):
   ....:     print(index, item)
   ....:     if not item % 2:
   ....:         b.remove(item)
   ....:         
(0, 2) # 这里没有问题 2被删除了
(1, 5) # 因为2被删除目前的列表是[4, 5, 6], 所以索引list[1]直接去找5, 忽略了4
(2, 6)

In [55]: my_list = [1, 2, 3, 4, 5]

In [56]: my_list[5] # 根本没有这个元素
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-56-037d00de8360> in <module>()
----> 1 my_list[5]

IndexError: list index out of range # 抛异常了

In [57]: my_list[5:] # 但是可以这样， 一定要注意, 用好了是trick,用错了就是坑啊
Out[57]: []

In [58]: def my_func():
   ....:         print(var) # 我可以先调用一个未定义的变量
   ....:     

In [59]: var = 'global' # 后赋值

In [60]: my_func() # 反正只要调用函数时候变量被定义了就可以了
global

In [61]: def my_func():
   ....:     var = 'locally changed'
   ....:     

In [62]: var = 'global'

In [63]: my_func()

In [64]: print(var)
global # 局部变量没有影响到全局变量

In [65]: def my_func():
   ....:         print(var) # 虽然你全局设置这个变量, 但是局部变量有同名的, python以为你忘了定义本地变量了
   ....:         var = 'locally changed'
   ....:         

In [66]: var = 'global'

In [67]: my_func()
---------------------------------------------------------------------------
UnboundLocalError                         Traceback (most recent call last)
<ipython-input-67-d82eda95de40> in <module>()
----> 1 my_func()

<ipython-input-65-0ad11d690936> in my_func()
      1 def my_func():
----> 2         print(var)
      3         var = 'locally changed'
      4 

UnboundLocalError: local variable 'var' referenced before assignment

In [68]: def my_func():
   ....:         global var # 这个时候得加全局了
   ....:         print(var) # 这样就能正常使用
   ....:         var = 'locally changed' 
   ....:     

In [69]: var = 'global'

In [70]: 

In [70]: my_func()
global

In [71]: print(var)
locally changed # 但是使用了global就改变了全局变量

In [72]: my_list1 = [[1, 2, 3]] * 2

In [73]: my_list1
Out[73]: [[1, 2, 3], [1, 2, 3]]

In [74]: my_list1[1][0] = 'a' # 我只修改子列表中的一项

In [75]: my_list1
Out[75]: [['a', 2, 3], ['a', 2, 3]] # 但是都影响到了

In [76]: my_list2 = [[1, 2, 3] for i in range(2)] # 用这种循环生成不同对象的方法就不影响了

In [77]: my_list2[1][0] = 'a'

In [78]: my_list2
Out[78]: [[1, 2, 3], ['a', 2, 3]]

In [1]: class A(object):
   ...:         def foo(self):
   ...:                 print("class A")
   ...:         

In [2]: class B(object):
   ...:         def foo(self):
   ...:                 print("class B")
   ...:         

In [3]: class C(A, B):
   ...:         pass
   ...: 

In [4]: C().foo()
class A # 例子很好懂, C继承了A和B，从左到右,发现A有foo方法,返回了

In [5]: class A(object):
   ...:        def foo(self):
   ...:               print("class A")
   ...:         

In [6]: class B(A):
   ...:        pass
   ...: 

In [7]: class C(A):
   ...:        def foo(self):
   ...:               print("class C")
   ...:         

In [8]: class D(B,C):
   ...:        pass
   ...: 

In [9]: D().foo()
class C # ? 按道理, 顺序是 D->B->A,为什么找到了C哪去了

In [10]: D.__mro__
Out[10]: (__main__.D, __main__.B, __main__.C, __main__.A, object)

In [17]: print('ID:', id(a_list))
('ID:', 4481323592)

In [18]: a_list += [1]

In [19]: print('ID (+=):', id(a_list))
('ID (+=):', 4481323592) # 使用+= 还是在原来的列表上操作

In [20]: a_list = a_list + [2]

In [21]: print('ID (list = list + ...):', id(a_list))
('ID (list = list + ...):', 4481293056) # 简单的+其实已经改变了原有列表
In [28]: a_list = []

In [29]: id(a_list)
Out[29]: 4481326976

In [30]: a_list.append(1)

In [31]: id(a_list)
Out[31]: 4481326976 # append 是在原有列表添加

In [32]: a_list.extend([2])

In [33]: id(a_list)
Out[33]: 4481326976 # extend 也是在原有列表上添加

In [34]: import datetime

In [35]: print('"datetime.time(0,0,0)" (Midnight) ->', bool(datetime.time(0,0,0)))
('"datetime.time(0,0,0)" (Midnight) ->', False)

In [36]: print('"datetime.time(1,0,0)" (1 am) ->', bool(datetime.time(1,0,0)))
('"datetime.time(1,0,0)" (1 am) ->', True)

In [37]: a = 1

In [38]: b = 1

In [39]: print('a is b', bool(a is b))
('a is b', True)

In [40]: c = 999

In [41]: d = 999

In [42]: print('c is d', bool(c is d))
('c is d', False) # 原因是python的内存管理,缓存了-5 - 256的对象

In [43]: print('256 is 257-1', 256 is 257-1)
('256 is 257-1', True)

In [44]: print('257 is 258-1', 257 is 258 - 1)
('257 is 258-1', False)

In [45]: print('-5 is -6+1', -5 is -6+1)
('-5 is -6+1', True)

In [46]: print('-7 is -6-1', -7 is -6-1)
('-7 is -6-1', False)
In [47]: a = 'hello world!'

In [48]: b = 'hello world!'

In [49]: print('a is b,', a is b)
('a is b,', False) # 很明显 他们没有被缓存,这是2个字段串的对象

In [50]: print('a == b,', a == b)
('a == b,', True) # 但他们的值相同
# But, 有个特例
In [51]: a = float('nan')

In [52]: print('a is a,', a is a)
('a is a,', True)

In [53]: print('a == a,', a == a)
('a == a,', False) # 亮瞎我眼睛了~

In [65]: list1 = [1, 2]

In [66]: list2 = list1 # 就是个引用, 你操作list2,其实list1的结果也会变

In [67]: list3 = list1[:]

In [69]: import copy

In [70]: list4 = copy.copy(list1) # 他和list3一样 都是浅拷贝

In [71]: id(list1), id(list2), id(list3), id(list4)
Out[71]: (4480620232, 4480620232, 4479667880, 4494894720)

In [72]: list2[0] = 3

In [73]: print('list1:', list1)
('list1:', [3, 2])

In [74]: list3[0] = 4

In [75]: list4[1] = 4

In [76]: print('list1:', list1)
('list1:', [3, 2]) # 对list3和list4操作都没有对list1有影响

# 再看看深拷贝和浅拷贝的区别

In [88]: from copy import copy, deepcopy

In [89]: list1 = [[1], [2]]

In [90]: list2 = copy(list1) # 还是浅拷贝

In [91]: list3 = deepcopy(list1) # 深拷贝

In [92]: id(list1), id(list2), id(list3)
Out[92]: (4494896592, 4495349160, 4494896088)

In [93]: list2[0][0] = 3

In [94]: print('list1:', list1)
('list1:', [[3], [2]]) # 看到了吧 假如你操作其子对象 还是和引用一样 影响了源

In [95]: list3[0][0] = 5

In [96]: print('list1:', list1)
('list1:', [[3], [2]]) # 深拷贝就不会影响

In [97]: isinstance(True, int)
Out[97]: True

In [98]: True + True
Out[98]: 2

In [99]: 3 * True + True
Out[99]: 4

In [100]: 3 * True - False
Out[100]: 3

In [104]: True << 10
Out[104]: 1024

In [111]: tup = ([],)

In [112]: tup[0] += [1]
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-112-d4f292cf35de> in <module>()
----> 1 tup[0] += [1]

TypeError: 'tuple' object does not support item assignment

In [113]: tup
Out[113]: ([1],) # 我靠 又是亮瞎我眼睛,明明抛了异常 还能修改?

In [114]: tup = ([],)

In [115]: tup[0].extend([1])

In [116]: tup[0]
Out[116]: [1] # 好吧,我有点看明白了, 虽然我不能直接操作元组，但是不能阻止我操作元组中可变的子对象(list)

In [117]: my_tup = (1,)

In [118]: my_tup += (4,)

In [119]: my_tup = my_tup + (5,)

In [120]: my_tup
Out[120]: (1, 4, 5) # ? 嗯 不是不能操作元组嘛?

In [121]: my_tup = (1,)

In [122]: print(id(my_tup))
4481317904

In [123]: my_tup += (4,)

In [124]: print(id(my_tup))
4480606864 # 操作的不是原来的元组 所以可以

In [125]: my_tup = my_tup + (5,)

In [126]: print(id(my_tup))
4474234912

In [127]: class my_class(object^E):
   .....:     def public_method(self):
   .....:         print('Hello public world!')
   .....:     def __private_method(self): # 私有以双下划线开头
   .....:         print('Hello private world!')
   .....:     def call_private_method_in_class(self):
   .....:         self.__private_method()

In [132]: my_instance = my_class()

In [133]: my_instance.public_method()
Hello public world! # 普通方法

In [134]: my_instance._my_class__private_method()
Hello private world! # 私有的可以加"_ + 类名字 + 私有方法名字”

In [135]: my_instance.call_private_method_in_class()
Hello private world! # 还可以通过类提供的公有接口内部访问

In [136]: my_instance._my_class__private_variable
Out[136]: 1

In [150]: try:
   .....:     print('third element:', a_list[2])
   .....: except IndexError:
   .....:     print('raised IndexError')
   .....: else:
   .....:     print('no error in try-block') # 只有在try里面没有异常的时候才会执行else里面的表达式
   .....:     
raised IndexError # 抛异常了 没完全完成
In [153]: i = 0

In [154]: while i < 2:
   .....:     print(i)
   .....:     i += 1
   .....: else:
   .....:     print('in else')
   .....:     
0
1
in else # while也支持哦~
In [155]: i = 0

In [156]: while i < 2:
   .....:         print(i)
   .....:         i += 1
   .....:         break
   .....: else:
   .....:         print('completed while-loop')
   .....:     
0 # 被break了 没有完全执行完 就不执行else里面的了
In [158]: for i in range(2):
   .....:         print(i)
   .....: else:
   .....:         print('completed for-loop')
   .....:     
0
1
completed for-loop

In [159]: for i in range(2):
   .....:         print(i)
   .....:         break
   .....: else:
   .....:         print('completed for-loop')
   .....:     
0 # 也是因为break了