pip install nbdev

# lib_name = your_project_name
# user = your_github_username
# description = A description of your project
# keywords = some keywords
# author = Your Name
# author_email = email@example.com
# copyright = Your Name or Company Name

nbdev_install_git_hooks

# default_exp core

#export
def say_hello(to):
    "Say hello to somebody"
    return f'Hello {to}!'

assert say_hello("Jeremy")=="Hello Jeremy!"

from nbdev.export import *
notebook2script()

$ nbdev_build_docs
converting: /home/jhoward/git/nbdev/nbs/00_core.ipynb
converting: /home/jhoward/git/nbdev/nbs/index.ipynb

pip install flask-restful需要Flask 0.10

保存为api.py之后运行：

from flask import Flask, request
from flask_restful import Resource, Api

app = Flask(__name__)
api = Api(app)

todos = {}

class TodoSimple(Resource):
    def get(self, todo_id):
        return {todo_id: todos[todo_id]}

    def put(self, todo_id):
        todos[todo_id] = request.form['data']
        return {todo_id: todos[todo_id]}

api.add_resource(TodoSimple, '/<string:todo_id>')

if __name__ == '__main__':
    app.run(debug=True)

$ curl http://localhost:5000/todo1 -d "data=Remember the milk" -X PUT
{"todo1": "Remember the milk"}
$ curl http://localhost:5000/todo1
{"todo1": "Remember the milk"}
$ curl http://localhost:5000/todo2 -d "data=Change my brakepads" -X PUT
{"todo2": "Change my brakepads"}
$ curl http://localhost:5000/todo2
{"todo2": "Change my brakepads"}

>>> from requests import put, get
>>> put('http://localhost:5000/todo1', data={'data': 'Remember the milk'}).json()
{u'todo1': u'Remember the milk'}
>>> get('http://localhost:5000/todo1').json()
{u'todo1': u'Remember the milk'}
>>> put('http://localhost:5000/todo2', data={'data': 'Change my brakepads'}).json()
{u'todo2': u'Change my brakepads'}
>>> get('http://localhost:5000/todo2').json()
{u'todo2': u'Change my brakepads'}

class Todo1(Resource):
    def get(self):
        # Default to 200 OK
        return {'task': 'Hello world'}

class Todo2(Resource):
    def get(self):
        # Set the response code to 201
        return {'task': 'Hello world'}, 201

class Todo3(Resource):
    def get(self):
        # Set the response code to 201 and return custom headers
        return {'task': 'Hello world'}, 201, {'Etag': 'some-opaque-string'}

api.add_resource(HelloWorld,
    '/',
    '/hello')

api.add_resource(Todo,
    '/todo/<int:todo_id>', endpoint='todo_ep')

from flask_restful import reqparse

parser = reqparse.RequestParser()
parser.add_argument('rate', type=int, help='Rate to charge for this resource')
args = parser.parse_args()

$ curl -d 'rate=foo' http://127.0.0.1:5000/todos
{'status': 400, 'message': 'foo cannot be converted to int'}

args = parser.parse_args(strict=True)

from flask_restful import fields, marshal_with

resource_fields = {
    'task':   fields.String,
    'uri':    fields.Url('todo_ep')
}

class TodoDao(object):
    def __init__(self, todo_id, task):
        self.todo_id = todo_id
        self.task = task

        # This field will not be sent in the response
        self.status = 'active'

class Todo(Resource):
    @marshal_with(resource_fields)
    def get(self, **kwargs):
        return TodoDao(todo_id='my_todo', task='Remember the milk')

from flask import Flask
from flask_restful import reqparse, abort, Api, Resource

app = Flask(__name__)
api = Api(app)

TODOS = {
    'todo1': {'task': 'build an API'},
    'todo2': {'task': '?????'},
    'todo3': {'task': 'profit!'},
}


def abort_if_todo_doesnt_exist(todo_id):
    if todo_id not in TODOS:
        abort(404, message="Todo {} doesn't exist".format(todo_id))

parser = reqparse.RequestParser()
parser.add_argument('task')


# Todo
# shows a single todo item and lets you delete a todo item
class Todo(Resource):
    def get(self, todo_id):
        abort_if_todo_doesnt_exist(todo_id)
        return TODOS[todo_id]

    def delete(self, todo_id):
        abort_if_todo_doesnt_exist(todo_id)
        del TODOS[todo_id]
        return '', 204

    def put(self, todo_id):
        args = parser.parse_args()
        task = {'task': args['task']}
        TODOS[todo_id] = task
        return task, 201


# TodoList
# shows a list of all todos, and lets you POST to add new tasks
class TodoList(Resource):
    def get(self):
        return TODOS

    def post(self):
        args = parser.parse_args()
        todo_id = int(max(TODOS.keys()).lstrip('todo')) + 1
        todo_id = 'todo%i' % todo_id
        TODOS[todo_id] = {'task': args['task']}
        return TODOS[todo_id], 201

##
## Actually setup the Api resource routing here
##
api.add_resource(TodoList, '/todos')
api.add_resource(Todo, '/todos/<todo_id>')


if __name__ == '__main__':
    app.run(debug=True)

$ python api.py
 * Running on http://127.0.0.1:5000/
 * Restarting with reloader

$ curl http://localhost:5000/todos
{"todo1": {"task": "build an API"}, "todo3": {"task": "profit!"}, "todo2": {"task": "?????"}}

$ curl http://localhost:5000/todos/todo3
{"task": "profit!"}

$ curl http://localhost:5000/todos/todo2 -X DELETE -v

> DELETE /todos/todo2 HTTP/1.1
> User-Agent: curl/7.19.7 (universal-apple-darwin10.0) libcurl/7.19.7 OpenSSL/0.9.8l zlib/1.2.3
> Host: localhost:5000
> Accept: */*
>
* HTTP 1.0, assume close after body
< HTTP/1.0 204 NO CONTENT
< Content-Type: application/json
< Content-Length: 0
< Server: Werkzeug/0.8.3 Python/2.7.2
< Date: Mon, 01 Oct 2012 22:10:32 GMT

$ curl http://localhost:5000/todos -d "task=something new" -X POST -v

> POST /todos HTTP/1.1
> User-Agent: curl/7.19.7 (universal-apple-darwin10.0) libcurl/7.19.7 OpenSSL/0.9.8l zlib/1.2.3
> Host: localhost:5000
> Accept: */*
> Content-Length: 18
> Content-Type: application/x-www-form-urlencoded
>
* HTTP 1.0, assume close after body
< HTTP/1.0 201 CREATED
< Content-Type: application/json
< Content-Length: 25
< Server: Werkzeug/0.8.3 Python/2.7.2
< Date: Mon, 01 Oct 2012 22:12:58 GMT
<
* Closing connection #0
{"task": "something new"}

$ curl http://localhost:5000/todos/todo3 -d "task=something different" -X PUT -v

> PUT /todos/todo3 HTTP/1.1
> Host: localhost:5000
> Accept: */*
> Content-Length: 20
> Content-Type: application/x-www-form-urlencoded
>
* HTTP 1.0, assume close after body
< HTTP/1.0 201 CREATED
< Content-Type: application/json
< Content-Length: 27
< Server: Werkzeug/0.8.3 Python/2.7.3
< Date: Mon, 01 Oct 2012 22:13:00 GMT
<
* Closing connection #0
{"task": "something different"}

        （1）如果“attr”是出现在Clz或其基类的__dict__中， 且attr是data descriptor， 那么调用其__get__方法, 否则
        （2）如果“attr”出现在obj的__dict__中， 那么直接返回 obj.__dict__['attr']， 否则
        （3）如果“attr”出现在Clz或其基类的__dict__中
            （3.1）如果attr是non-data descriptor，那么调用其__get__方法， 否则
            （3.2）返回 __dict__['attr']
        （4）如果Clz有__getattr__方法，调用__getattr__方法，否则
        （5）抛出AttributeError 

　　下面是测试代码： ```    
#coding=utf-8
class DataDescriptor(object):
    def __init__(self, init_value):
        self.value = init_value
  
    def __get__(self, instance, typ):
        return 'DataDescriptor __get__'
  
    def __set__(self, instance, value):
        print ('DataDescriptor __set__')
        self.value = value
 
class NonDataDescriptor(object):
    def __init__(self, init_value):
        self.value = init_value

    def __get__(self, instance, typ):
        return('NonDataDescriptor __get__')
 
class Base(object):
    dd_base = DataDescriptor(0)
    ndd_base = NonDataDescriptor(0)

 
class Derive(Base):
    dd_derive = DataDescriptor(0)
    ndd_derive = NonDataDescriptor(0)
    same_name_attr = 'attr in class'
 
    def __init__(self):
        self.not_des_attr = 'I am not descriptor attr'
        self.same_name_attr = 'attr in object'
 
    def __getattr__(self, key):
        return '__getattr__ with key %s' % key
 
    def change_attr(self):
        self.__dict__['dd_base'] = 'dd_base now in object dict '
        self.__dict__['ndd_derive'] = 'ndd_derive now in object dict '
 
def main():
    b = Base()
    d = Derive()
    print('Derive object dict', d.__dict__)
    assert d.dd_base == "DataDescriptor __get__"
    assert d.ndd_derive == 'NonDataDescriptor __get__'
    assert d.not_des_attr == 'I am not descriptor attr'
    assert d.no_exists_key == '__getattr__ with key no_exists_key'
    assert d.same_name_attr == 'attr in object'
    d.change_attr()
    print('Derive object dict', d.__dict__)
    assert d.dd_base != 'dd_base now in object dict '
    assert d.ndd_derive == 'ndd_derive now in object dict '

    try:
        b.no_exists_key
    except Exception, e:
        assert isinstance(e, AttributeError)
 
if __name__ == '__main__':
    main() ```
    调用change_attr方法之后，dd_base既出现在类的__dict__（作为data descriptor）, 也出现在实例的__dict__， 因为attribute lookup的循序，所以优先返回的还是Clz.__dict__['dd_base']。而ndd_base虽然出现在类的__dict__， 但是因为是nondata descriptor，所以优先返回obj.__dict__['dd_base']。其他：line48,line56表明了__getattr__的作用。line49表明obj.__dict__优先于Clz.__dict__
    前面提到过，类也是对象，类是元类（metaclass）的实例，所以类属性的查找顺序基本同上，区别在于第二步，由于Clz可能有基类，所以是在Clz及其基类的__dict__查找“attr"<br>
    补充说明：很多网上说属性最高优先级是__getattribute__。但一般我们不会去覆盖__getattribute__，因为一旦覆盖了__getattribute__，所有后面的规则都失效了，所有要理解上面提到的"生在__getattribute__内部"。<br>
   再看以下代码： ```       
import functools, time
class cached_property(object):
    """ A property that is only computed once per instance and then replaces
        itself with an ordinary attribute. Deleting the attribute resets the
        property. """

    def __init__(self, func):
        functools.update_wrapper(self, func)
        self.func = func

    def __get__(self, obj, cls):
        if obj is None: return self
        value = obj.__dict__[self.func.__name__] = self.func(obj)
        return value

class TestClz(object):
    @cached_property
    def complex_calc(self):
        print('very complex_calc')
        return sum(range(100))

if __name__=='__main__':
    t = TestClz()
    print('>>> first call')
    print(t.complex_calc)
    print('>>> second call')
    print(t.complex_calc) ```
cached_property是一个non-data descriptor。在TestClz中，用cached_property装饰方法complex_calc，返回值是一个descriptor实例，所以在调用的时候没有使用小括号。第一次调用t.complex_calc之前，obj(t)的__dict__中没有”complex_calc“， 根据查找顺序第三条，执行cached_property.__get__, 这个函数代用缓存的complex_calc函数计算出结果，并且把结果放入obj.__dict__。那么第二次访问t.complex_calc的时候，根据查找顺序，第二条有限于第三条，所以就直接返回obj.__dict__['complex_calc']。<br> 再举一个网上常见的例子： ```
class NotNegative():
    def __init__(self,name):
        self.name = name

    def __set__(self, instance, value):
        if value < 0:
            raise ValueError(self.name+' must be >= 0')
        else:
            instance.__dict__[self.name] = value

class Product():
    quantity = NotNegative('quantity')
    price = NotNegative('price')

    def __init__(self,name,quantity,price):
        self.name = name
        self.quantity = quantity
        self.price = price

book = Product('mybook',2,5) ```
    通过描述符来限制设置quantity和price必须是非负。在该例子中，如果执行book.quantity=3,解释器会先查找实例属性，发现有quantity属性，但是解释器又发现同样有一个类属性是描述符，于是解释器最终会选择走描述符这条路。然后因为是描述符，于是会执行描述符中的set特殊方法。<br>

    描述符中的set特殊方法的参数有为<br> ```        
    self ：是描述符实例
    instance ：是相当于例子中的实例book
    value ：就是要赋予的值 ``` get方法同样有3个参数self, instance, owner。self，instance与set中的相同，owner为例子中的Product类<br>