py3_cookbook_notes_02

def avg(first, *rest):
    return (first + sum(rest)) / (1 + len(rest))

# Sample use
avg(1, 2) # 1.5
avg(1, 2, 3, 4) # 2.5

import html

def make_element(name, value, **attrs):
    keyvals = [' %s="%s"' % item for item in attrs.items()]
    attr_str = ''.join(keyvals)
    element = '<{name}{attrs}>{value}</{name}>'.format(
                name=name,
                attrs=attr_str,
                value=html.escape(value))
    return element

# Example
# Creates '<item size="large" quantity="6">Albatross</item>'
make_element('item', 'Albatross', size='large', quantity=6)

# Creates '<p>&lt;spam&gt;</p>'
make_element('p', '<spam>')

def recv(maxsize, *, block):
    'Receives a message'
    pass

recv(1024, True) # TypeError
recv(1024, block=True) # Ok

def mininum(*values, clip=None):
    m = min(values)
    if clip is not None:
        m = clip if clip > m else m
    return m

minimum(1, 5, 2, -5, 10) # Returns -5
minimum(1, 5, 2, -5, 10, clip=0) # Returns 0

def add(x:int, y:int) -> int:
    return x + y

>>> add = lambda x, y: x + y
>>> add(2,3)
5
>>> add('hello', 'world')
'helloworld'

>>> names = ['David Beazley', 'Brian Jones',
...         'Raymond Hettinger', 'Ned Batchelder']
>>> sorted(names, key=lambda name: name.split()[-1].lower())
['Ned Batchelder', 'David Beazley', 'Raymond Hettinger', 'Brian Jones']

>>> x = 10
>>> a = lambda y, x=x: x + y
>>> x = 20
>>> b = lambda y, x=x: x + y
>>> a(10)
20
>>> b(10)
30

def spam(a, b, c, d):
    print(a, b, c, d)
    
>>> from functools import partial
>>> s1 = partial(spam, 1) # a = 1
>>> s1(2, 3, 4)
1 2 3 4
>>> s2 = partial(spam, d=42) # d = 42
>>> s2(1, 2, 3)
1 2 3 42
>>> s2(4, 5, 5)
4 5 5 42
>>> s3 = partial(spam, 1, 2, d=42) # a = 1, b = 2, d = 42
>>> s3(3)

from urllib.request import urlopen

class UrlTemplate:
    def __init__(self, template):
        self.template = template

    def open(self, **kwargs):
        return urlopen(self.template.format_map(kwargs))

# Example use. Download stock data from yahoo
yahoo = UrlTemplate('http://finance.yahoo.com/d/quotes.csv?s={names}&f={fields}')
for line in yahoo.open(names='IBM,AAPL,FB', fields='sl1c1v'):
    print(line.decode('utf-8'))

from urllib.request import urlopen

def urltemplate(template):
    def opener(**kwargs):
        return urlopen(template.format_map(kwargs))
    return opener

# Example use
yahoo = urltemplate('http://finance.yahoo.com/d/quotes.csv?s={names}&f={fields}')
for line in yahoo(names='IBM,AAPL,FB', fields='sl1c1v'):
    print(line.decode('utf-8'))

>>> def add(x, y):
...     return x + y
...
class ResultHandler:

    def __init__(self):
        self.sequence = 0

    def handler(self, result):
        self.sequence += 1
        print('[{}] Got: {}'.format(self.sequence, result))

>>> r = ResultHandler()
>>> apply_async(add, (2, 3), callback=r.handler)
[1] Got: 5

>>> def add(x, y):
...     return x + y
...
def make_handler():
    sequence = 0
    def handler(result):
        nonlocal sequence
        sequence += 1
        print('[{}] Got: {}'.format(sequence, result))
    return handler
>>> handler = make_handler()
>>> apply_async(add, (2, 3), callback=handler)

def apply_async(func, args, *, callback):
    # Compute the result
    result = func(*args)

    # Invoke the callback with the result
    callback(result)

class Async:
    def __init__(self, func, args):
        self.func = func
        self.args = args

def inlined_async(func):
    @wraps(func)
    def wrapper(*args):
        f = func(*args) # func is test function, f is a generator
        result_queue = Queue()
        result_queue.put(None)
        while True:
            result = result_queue.get()
            try:
                a = f.send(result) # a is Async object
                apply_async(a.func, a.args, callback=result_queue.put)
            except StopIteration:
                break
    return wrapper

def add(x, y):
    return x + y

@inlined_async
def test():
    r = yield Async(add, (2, 3))
    print(r)
    r = yield Async(add, ('hello', 'world'))
    print(r)
    for n in range(10):
        r = yield Async(add, (n, n))
        print(r)
    print('Goodbye')

test()

def sample():
    n = 0
    # Closure function
    def func():
        print('n=', n)

    # Accessor methods for n
    def get_n():
        return n

    def set_n(value):
        nonlocal n
        n = value

    # Attach as function attributes
    func.get_n = get_n
    func.set_n = set_n
    return func

class Pair:
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def __repr__(self):
        return 'Pair({0.x!r}, {0.y!r})'.format(self)

    def __str__(self):
        return '({0.x!s}, {0.y!s})'.format(self)

_formats = {
    'ymd' : '{d.year}-{d.month}-{d.day}',
    'mdy' : '{d.month}/{d.day}/{d.year}',
    'dmy' : '{d.day}/{d.month}/{d.year}'
    }

class Date:
    def __init__(self, year, month, day):
        self.year = year
        self.month = month
        self.day = day

    def __format__(self, code):
        if code == '':
            code = 'ymd'
        fmt = _formats[code]
        return fmt.format(d=self)
      
>>> d = Date(2012, 12, 21)
>>> format(d)
'2012-12-21'
>>> format(d, 'mdy')
'12/21/2012'
>>> 'The date is {:ymd}'.format(d)
'The date is 2012-12-21'
>>> 'The date is {:mdy}'.format(d)
'The date is 12/21/2012'

from socket import socket, AF_INET, SOCK_STREAM

class LazyConnection:
    def __init__(self, address, family=AF_INET, type=SOCK_STREAM):
        self.address = address
        self.family = family
        self.type = type
        self.sock = None

    def __enter__(self):
        if self.sock is not None:
            raise RuntimeError('Already connected')
        self.sock = socket(self.family, self.type)
        self.sock.connect(self.address)
        return self.sock

    def __exit__(self, exc_ty, exc_val, tb):
        self.sock.close()
        self.sock = None
        
from functools import partial

conn = LazyConnection(('www.python.org', 80))
# Connection closed
with conn as s:
    # conn.__enter__() executes: connection open
    s.send(b'GET /index.html HTTP/1.0\r\n')
    s.send(b'Host: www.python.org\r\n')
    s.send(b'\r\n')
    resp = b''.join(iter(partial(s.recv, 8192), b''))
    # conn.__exit__() executes: connection closed

class A:
    def __init__(self):
        self._internal = 0 # An internal attribute
        self.public = 1 # A public attribute
        self.__private_field = 0 # 不能被子类覆盖

    def public_method(self):
        '''
        A public method
        '''
        pass

    def _internal_method(self):
        pass
      
    def __private_method(self):
        pass

class Person:
    def __init__(self, first_name):
        self.first_name = first_name

    # Getter function
    @property
    def first_name(self):
        return self._first_name

    # Setter function
    @first_name.setter
    def first_name(self, value):
        if not isinstance(value, str):
            raise TypeError('Expected a string')
        self._first_name = value

    # Deleter function (optional)
    @first_name.deleter
    def first_name(self):
        raise AttributeError("Can't delete attribute")

class A:
    def spam(self):
        print('A.spam')

class B(A):
    def spam(self):
        print('B.spam')
        super().spam()  # Call parent spam()

class Structure:
    # Class variable that specifies expected fields
    _fields = []

    def __init__(self, *args, **kwargs):
        if len(args) != len(self._fields):
            raise TypeError('Expected {} arguments'.format(len(self._fields)))

        # Set the arguments
        for name, value in zip(self._fields, args):
            setattr(self, name, value)

        # Set the additional arguments (if any)
        extra_args = kwargs.keys() - self._fields
        for name in extra_args:
            setattr(self, name, kwargs.pop(name))

        if kwargs:
            raise TypeError('Duplicate values for {}'.format(','.join(kwargs)))
            
class Stock(Structure):
        _fields = ['name', 'shares', 'price']

    s1 = Stock('ACME', 50, 91.1)
    s2 = Stock('ACME', 50, 91.1, date='8/2/2012')

from abc import ABCMeta, abstractmethod

class IStream(metaclass=ABCMeta):
    @abstractmethod
    def read(self, maxbytes=-1):
        pass

    @abstractmethod
    def write(self, data):
        pass

class SocketStream(IStream):
    def read(self, maxbytes=-1):
        pass

    def write(self, data):
        pass

# Register the built-in I/O classes as supporting our interface
import io
IStream.register(io.IOBase)

import collections

# Check if x is a sequence
if isinstance(x, collections.Sequence):
...

# Check if x is iterable
if isinstance(x, collections.Iterable):
...

# Check if x has a size
if isinstance(x, collections.Sized):
...

# Check if x is a mapping
if isinstance(x, collections.Mapping):

# Base class. Uses a descriptor to set a value
class Descriptor:
    def __init__(self, name=None, **opts):
        self.name = name
        for key, value in opts.items():
            setattr(self, key, value)

    def __set__(self, instance, value):
        instance.__dict__[self.name] = value


# Descriptor for enforcing types
class Typed(Descriptor):
    expected_type = type(None)

    def __set__(self, instance, value):
        if not isinstance(value, self.expected_type):
            raise TypeError('expected ' + str(self.expected_type))
        super().__set__(instance, value)


# Descriptor for enforcing values
class Unsigned(Descriptor):
    def __set__(self, instance, value):
        if value < 0:
            raise ValueError('Expected >= 0')
        super().__set__(instance, value)


class MaxSized(Descriptor):
    def __init__(self, name=None, **opts):
        if 'size' not in opts:
            raise TypeError('missing size option')
        super().__init__(name, **opts)

    def __set__(self, instance, value):
        if len(value) >= self.size:
            raise ValueError('size must be < ' + str(self.size))
        super().__set__(instance, value)
        
class Integer(Typed):
    expected_type = int

class UnsignedInteger(Integer, Unsigned):
    pass

class Float(Typed):
    expected_type = float

class UnsignedFloat(Float, Unsigned):
    pass

class String(Typed):
    expected_type = str

class SizedString(String, MaxSized):
    pass

class Stock:
    # Specify constraints
    name = SizedString('name', size=8)
    shares = UnsignedInteger('shares')
    price = UnsignedFloat('price')

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

import collections
class A(collections.Iterable):
    def __iter__():
      pass

class A:
    def spam(self, x):
        pass

    def foo(self):
        pass
      
class B2:
    """使用__getattr__的代理，代理方法比较多时候"""

    def __init__(self):
        self._a = A()

    def bar(self):
        pass

    # Expose all of the methods defined on class A
    def __getattr__(self, name):
        """这个方法在访问的attribute不存在的时候被调用
        the __getattr__() method is actually a fallback method
        that only gets called when an attribute is not found"""
        return getattr(self._a, name)

import time

class Date:
    """方法一：使用类方法"""
    # Primary constructor
    def __init__(self, year, month, day):
        self.year = year
        self.month = month
        self.day = day

    # Alternate constructor
    @classmethod
    def today(cls):
        t = time.localtime()
        return cls(t.tm_year, t.tm_mon, t.tm_mday)

class Date:
    def __init__(self, year, month, day):
        self.year = year
        self.month = month
        self.day = day

d = Date.__new__(Date)
>>> data = {'year':2012, 'month':8, 'day':29}
>>> for key, value in data.items():
...     setattr(d, key, value)
...

def LoggedMapping(cls):
    """第二种方式：使用类装饰器"""
    cls_getitem = cls.__getitem__
    cls_setitem = cls.__setitem__
    cls_delitem = cls.__delitem__

    def __getitem__(self, key):
        print('Getting ' + str(key))
        return cls_getitem(self, key)

    def __setitem__(self, key, value):
        print('Setting {} = {!r}'.format(key, value))
        return cls_setitem(self, key, value)

    def __delitem__(self, key):
        print('Deleting ' + str(key))
        return cls_delitem(self, key)

    cls.__getitem__ = __getitem__
    cls.__setitem__ = __setitem__
    cls.__delitem__ = __delitem__
    return cls


@LoggedMapping
class LoggedDict(dict):
    pass

class Connection:
    """新方案——对每个状态定义一个类"""

    def __init__(self):
        self.new_state(ClosedConnectionState)

    def new_state(self, newstate):
        self._state = newstate
        # Delegate to the state class

    def read(self):
        return self._state.read(self)

    def write(self, data):
        return self._state.write(self, data)

    def open(self):
        return self._state.open(self)

    def close(self):
        return self._state.close(self)


# Connection state base class
class ConnectionState:
    @staticmethod
    def read(conn):
        raise NotImplementedError()

    @staticmethod
    def write(conn, data):
        raise NotImplementedError()

    @staticmethod
    def open(conn):
        raise NotImplementedError()

    @staticmethod
    def close(conn):
        raise NotImplementedError()


# Implementation of different states
class ClosedConnectionState(ConnectionState):
    @staticmethod
    def read(conn):
        raise RuntimeError('Not open')

    @staticmethod
    def write(conn, data):
        raise RuntimeError('Not open')

    @staticmethod
    def open(conn):
        conn.new_state(OpenConnectionState)

    @staticmethod
    def close(conn):
        raise RuntimeError('Already closed')


class OpenConnectionState(ConnectionState):
    @staticmethod
    def read(conn):
        print('reading')

    @staticmethod
    def write(conn, data):
        print('writing')

    @staticmethod
    def open(conn):
        raise RuntimeError('Already open')

    @staticmethod
    def close(conn):
        conn.new_state(ClosedConnectionState)
        
c = Connection()
>>> c._state
<class '__main__.ClosedConnectionState'>
>>> c.open()
>>> c._state
<class '__main__.OpenConnectionState'>
>>> c.read()
reading
>>> c.write('hello')
writing
>>> c.close()
>>> c._state
<class '__main__.ClosedConnectionState'>
>>>

import math

class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def __repr__(self):
        return 'Point({!r:},{!r:})'.format(self.x, self.y)

    def distance(self, x, y):
        return math.hypot(self.x - x, self.y - y)


p = Point(2, 3)
d = getattr(p, 'distance')(0, 0)  # Calls p.distance(0, 0)

import operator
operator.methodcaller('distance', 0, 0)(p)

class Node:
    pass

class UnaryOperator(Node):
    def __init__(self, operand):
        self.operand = operand

class BinaryOperator(Node):
    def __init__(self, left, right):
        self.left = left
        self.right = right

class Add(BinaryOperator):
    pass

class Sub(BinaryOperator):
    pass

class Mul(BinaryOperator):
    pass

class Div(BinaryOperator):
    pass

class Negate(UnaryOperator):
    pass

class Number(Node):
    def __init__(self, value):
        self.value = value

class NodeVisitor:
    def visit(self, node):
        methname = 'visit_' + type(node).__name__
        meth = getattr(self, methname, None)
        if meth is None:
            meth = self.generic_visit
        return meth(node)

    def generic_visit(self, node):
        raise RuntimeError('No {} method'.format('visit_' + type(node).__name__))

class Evaluator(NodeVisitor):
    def visit_Number(self, node):
        return node.value

    def visit_Add(self, node):
        return self.visit(node.left) + self.visit(node.right)

    def visit_Sub(self, node):
        return self.visit(node.left) - self.visit(node.right)

    def visit_Mul(self, node):
        return self.visit(node.left) * self.visit(node.right)

    def visit_Div(self, node):
        return self.visit(node.left) / self.visit(node.right)

    def visit_Negate(self, node):
        return -node.operand
      
>>> e = Evaluator()
>>> e.visit(t4)

class HTTPHandler:
    def handle(self, request):
        methname = 'do_' + request.request_method
        getattr(self, methname)(request)
    def do_GET(self, request):
        pass
    def do_POST(self, request):
        pass
    def do_HEAD(self, request):
        pass

import types

class Node:
    pass

class NodeVisitor:
    def visit(self, node):
        stack = [node]
        last_result = None
        while stack:
            try:
                last = stack[-1]
                if isinstance(last, types.GeneratorType):
                    stack.append(last.send(last_result))
                    last_result = None
                elif isinstance(last, Node):
                    stack.append(self._visit(stack.pop()))
                else:
                    last_result = stack.pop()
            except StopIteration:
                stack.pop()

        return last_result

    def _visit(self, node):
        methname = 'visit_' + type(node).__name__
        meth = getattr(self, methname, None)
        if meth is None:
            meth = self.generic_visit
        return meth(node)

    def generic_visit(self, node):
        raise RuntimeError('No {} method'.format('visit_' + type(node).__name__))
        
class UnaryOperator(Node):
    def __init__(self, operand):
        self.operand = operand

class BinaryOperator(Node):
    def __init__(self, left, right):
        self.left = left
        self.right = right

class Add(BinaryOperator):
    pass

class Sub(BinaryOperator):
    pass

class Mul(BinaryOperator):
    pass

class Div(BinaryOperator):
    pass

class Negate(UnaryOperator):
    pass

class Number(Node):
    def __init__(self, value):
        self.value = value

# A sample visitor class that evaluates expressions
class Evaluator(NodeVisitor):
    def visit_Number(self, node):
        return node.value

    def visit_Add(self, node):
        yield (yield node.left) + (yield node.right)

    def visit_Sub(self, node):
        yield (yield node.left) - (yield node.right)

    def visit_Mul(self, node):
        yield (yield node.left) * (yield node.right)

    def visit_Div(self, node):
        yield (yield node.left) / (yield node.right)

    def visit_Negate(self, node):
        yield - (yield node.operand)
        
>>> a = Number(0)
>>> for n in range(1,100000):
...     a = Add(a, Number(n))
...
>>> e = Evaluator()
>>> e.visit(a)
4999950000

import weakref

class Node:
    def __init__(self, value):
        self.value = value
        self._parent = None
        self.children = []

    def __repr__(self):
        return 'Node({!r:})'.format(self.value)

    # property that manages the parent as a weak-reference
    @property
    def parent(self):
        return None if self._parent is None else self._parent()

    @parent.setter
    def parent(self, node):
        self._parent = weakref.ref(node)

    def add_child(self, child):
        self.children.append(child)
        child.parent = self
        
>>> root = Node('parent')
>>> c1 = Node('child')
>>> root.add_child(c1)
>>> print(c1.parent)
Node('parent')
>>> del root
>>> print(c1.parent)
None
>>>

from functools import total_ordering

class Room:
    def __init__(self, name, length, width):
        self.name = name
        self.length = length
        self.width = width
        self.square_feet = self.length * self.width

@total_ordering
class House:
    def __init__(self, name, style):
        self.name = name
        self.style = style
        self.rooms = list()

    @property
    def living_space_footage(self):
        return sum(r.square_feet for r in self.rooms)

    def add_room(self, room):
        self.rooms.append(room)

    def __str__(self):
        return '{}: {} square foot {}'.format(self.name,
                self.living_space_footage,
                self.style)

    def __eq__(self, other):
        return self.living_space_footage == other.living_space_footage

    def __lt__(self, other):
        return self.living_space_footage < other.living_space_footage

class CachedSpamManager:
    def __init__(self):
        self._cache = weakref.WeakValueDictionary()

    def get_spam(self, name):
        if name not in self._cache:
            temp = Spam._new(name)  # Modified creation
            self._cache[name] = temp
        else:
            temp = self._cache[name]
        return temp

    def clear(self):
            self._cache.clear()

class Spam:
    def __init__(self, *args, **kwargs):
        raise RuntimeError("Can't instantiate directly")

    # Alternate constructor
    @classmethod
    def _new(cls, name):
        self = cls.__new__(cls)
        self.name = name
        return self

import time
from functools import wraps

def timethis(func):
    '''
    Decorator that reports the execution time.
    '''
    @wraps(func)
    def wrapper(*args, **kwargs):
        start = time.time()
        result = func(*args, **kwargs)
        end = time.time()
        print(func.__name__, end-start)
        return result
    return wrapper
  
>>> @timethis
... def countdown(n):
...     '''
...     Counts down
...     '''
...     while n > 0:
...         n -= 1
...
... countdown(100000)
... countdown.__wrapped__(100000)

from functools import wraps, partial
import logging

def logged(func=None, *, level=logging.DEBUG, name=None, message=None):
    if func is None:
        return partial(logged, level=level, name=name, message=message)

    logname = name if name else func.__module__
    log = logging.getLogger(logname)
    logmsg = message if message else func.__name__

    @wraps(func)
    def wrapper(*args, **kwargs):
        log.log(level, logmsg)
        return func(*args, **kwargs)

    return wrapper

# Example use
@logged
def add(x, y):
    return x + y

@logged(level=logging.CRITICAL, name='example')
def spam():
    print('Spam!')

from inspect import signature
from functools import wraps

def typeassert(*ty_args, **ty_kwargs):
    def decorate(func):
        # If in optimized mode, disable type checking
        if not __debug__:
            return func

        # Map function argument names to supplied types
        sig = signature(func)
        bound_types = sig.bind_partial(*ty_args, **ty_kwargs).arguments

        @wraps(func)
        def wrapper(*args, **kwargs):
            bound_values = sig.bind(*args, **kwargs)
            # Enforce type assertions across supplied arguments
            for name, value in bound_values.arguments.items():
                if name in bound_types:
                    if not isinstance(value, bound_types[name]):
                        raise TypeError(
                            'Argument {} must be {}'.format(name, bound_types[name])
                            )
            return func(*args, **kwargs)
        return wrapper
    return decorate
  
>>> @typeassert(int, int)
... def add(x, y):
...     return x + y

import types
from functools import wraps

class Profiled:
    def __init__(self, func):
        wraps(func)(self)
        self.ncalls = 0

    def __call__(self, *args, **kwargs):
        self.ncalls += 1
        return self.__wrapped__(*args, **kwargs)

    def __get__(self, instance, cls):
        if instance is None:
            return self
        else:
            return types.MethodType(self, instance)

@Profiled
def add(x, y):
    return x + y

class Spam:
    @Profiled
    def bar(self, x):
        print(self, x)

>>> add(2, 3)
5
>>> add(4, 5)
9
>>> add.ncalls
2
>>> s = Spam()
>>> s.bar(1)
<__main__.Spam object at 0x10069e9d0> 1
>>> s.bar(2)
<__main__.Spam object at 0x10069e9d0> 2
>>> s.bar(3)
<__main__.Spam object at 0x10069e9d0> 3
>>> Spam.bar.ncalls
3

from functools import wraps

def optional_debug(func):
    @wraps(func)
    def wrapper(*args, debug=False, **kwargs):
        if debug:
            print('Calling', func.__name__)
        return func(*args, **kwargs)

    return wrapper

>>> @optional_debug
... def spam(a,b,c):
...     print(a,b,c)
...
>>> spam(1,2,3)
1 2 3
>>> spam(1,2,3, debug=True)
Calling spam
1 2 3
>>>

def log_getattribute(cls):
    # Get the original implementation
    orig_getattribute = cls.__getattribute__

    # Make a new definition
    def new_getattribute(self, name):
        print('getting:', name)
        return orig_getattribute(self, name)

    # Attach to the class and return
    cls.__getattribute__ = new_getattribute
    return cls

# Example use
@log_getattribute
class A:
    def __init__(self,x):
        self.x = x
    def spam(self):
        pass
      
>>> a = A(42)
>>> a.x
getting: x
42
>>> a.spam()
getting: spam
>>>

class NoInstances(type):
    def __call__(self, *args, **kwargs):
        raise TypeError("Can't instantiate directly")

# Example
class Spam(metaclass=NoInstances):
    @staticmethod
    def grok(x):
        print('Spam.grok')
        
>>> Spam.grok(42)
Spam.grok
>>> s = Spam()
Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
    File "example1.py", line 7, in __call__
        raise TypeError("Can't instantiate directly")
TypeError: Can't instantiate directly
>>>

class Singleton(type):
    def __init__(self, *args, **kwargs):
        self.__instance = None
        super().__init__(*args, **kwargs)

    def __call__(self, *args, **kwargs):
        if self.__instance is None:
            self.__instance = super().__call__(*args, **kwargs)
            return self.__instance
        else:
            return self.__instance

# Example
class Spam(metaclass=Singleton):
    def __init__(self):
        print('Creating Spam')

import weakref

class Cached(type):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.__cache = weakref.WeakValueDictionary()

    def __call__(self, *args):
        if args in self.__cache:
            return self.__cache[args]
        else:
            obj = super().__call__(*args)
            self.__cache[args] = obj
            return obj

# Example
class Spam(metaclass=Cached):
    def __init__(self, name):
        print('Creating Spam({!r})'.format(name))
        self.name = name

from collections import OrderedDict

# A set of descriptors for various types
class Typed:
    _expected_type = type(None)
    def __init__(self, name=None):
        self._name = name

    def __set__(self, instance, value):
        if not isinstance(value, self._expected_type):
            raise TypeError('Expected ' + str(self._expected_type))
        instance.__dict__[self._name] = value

class Integer(Typed):
    _expected_type = int

class Float(Typed):
    _expected_type = float

class String(Typed):
    _expected_type = str

# Metaclass that uses an OrderedDict for class body
class OrderedMeta(type):
    def __new__(cls, clsname, bases, clsdict):
        d = dict(clsdict)
        order = []
        for name, value in clsdict.items():
            if isinstance(value, Typed):
                value._name = name
                order.append(name)
        d['_order'] = order
        return type.__new__(cls, clsname, bases, d)

    @classmethod
    def __prepare__(cls, clsname, bases):
        return OrderedDict()
      
class Structure(metaclass=OrderedMeta):
    def as_csv(self):
        return ','.join(str(getattr(self,name)) for name in self._order)

# Example use
class Stock(Structure):
    name = String()
    shares = Integer()
    price = Float()

    def __init__(self, name, shares, price):
        self.name = name
        self.shares = shares
        self.price = price
        
>>> s = Stock('GOOG',100,490.1)
>>> s.name
'GOOG'
>>> s.as_csv()
'GOOG,100,490.1'
>>> t = Stock('AAPL','a lot', 610.23)
Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
    File "dupmethod.py", line 34, in __init__
TypeError: shares expects <class 'int'>
>>>

class MyMeta(type):
    # Optional
    @classmethod
    def __prepare__(cls, name, bases, *, debug=False, synchronize=False):
        # Custom processing
        pass
        return super().__prepare__(name, bases)

    # Required
    def __new__(cls, name, bases, ns, *, debug=False, synchronize=False):
        # Custom processing
        pass
        return super().__new__(cls, name, bases, ns)

    # Required
    def __init__(self, name, bases, ns, *, debug=False, synchronize=False):
        # Custom processing
        pass
        super().__init__(name, bases, ns)
        
class Spam(metaclass=MyMeta, debug=True, synchronize=True):
    pass

from inspect import Signature, Parameter

def make_sig(*names):
    parms = [Parameter(name, Parameter.POSITIONAL_OR_KEYWORD)
            for name in names]
    return Signature(parms)

class StructureMeta(type):
    def __new__(cls, clsname, bases, clsdict):
        clsdict['__signature__'] = make_sig(*clsdict.get('_fields',[]))
        return super().__new__(cls, clsname, bases, clsdict)

class Structure(metaclass=StructureMeta):
    _fields = []
    def __init__(self, *args, **kwargs):
        bound_values = self.__signature__.bind(*args, **kwargs)
        for name, value in bound_values.arguments.items():
            setattr(self, name, value)

# Example
class Stock(Structure):
    _fields = ['name', 'shares', 'price']

class Point(Structure):
    _fields = ['x', 'y']

from inspect import signature
import logging

class MatchSignaturesMeta(type):

    def __init__(self, clsname, bases, clsdict):
        super().__init__(clsname, bases, clsdict)
        sup = super(self, self)
        for name, value in clsdict.items():
            if name.startswith('_') or not callable(value):
                continue
            # Get the previous definition (if any) and compare the signatures
            prev_dfn = getattr(sup,name,None)
            if prev_dfn:
                prev_sig = signature(prev_dfn)
                val_sig = signature(value)
                if prev_sig != val_sig:
                    logging.warning('Signature mismatch in %s. %s != %s',
                                    value.__qualname__, prev_sig, val_sig)

# Example
class Root(metaclass=MatchSignaturesMeta):
    pass

class A(Root):
    def foo(self, x, y):
        pass

    def spam(self, x, *, z):
        pass

# Class with redefined methods, but slightly different signatures
class B(A):
    def foo(self, a, b):
        pass

    def spam(self,x,z):
        pass

import operator
import types
import sys

def named_tuple(classname, fieldnames):
    # Populate a dictionary of field property accessors
    cls_dict = { name: property(operator.itemgetter(n))
                for n, name in enumerate(fieldnames) }

    # Make a __new__ function and add to the class dict
    def __new__(cls, *args):
        if len(args) != len(fieldnames):
            raise TypeError('Expected {} arguments'.format(len(fieldnames)))
        return tuple.__new__(cls, args)

    cls_dict['__new__'] = __new__

    # Make the class
    cls = types.new_class(classname, (tuple,), {},
                        lambda ns: ns.update(cls_dict))

    # Set the module to that of the caller
    cls.__module__ = sys._getframe(1).f_globals['__name__']
    return cls

import operator

class StructTupleMeta(type):
    def __init__(cls, *args, **kwargs):
        super().__init__(*args, **kwargs)
        for n, name in enumerate(cls._fields):
            setattr(cls, name, property(operator.itemgetter(n)))

class StructTuple(tuple, metaclass=StructTupleMeta):
    _fields = []
    def __new__(cls, *args):
        if len(args) != len(cls._fields):
            raise ValueError('{} arguments required'.format(len(cls._fields)))
        return super().__new__(cls,args)
      
class Stock(StructTuple):
    _fields = ['name', 'shares', 'price']

class Point(StructTuple):
    _fields = ['x', 'y']
    
>>> s = Stock('ACME', 50, 91.1)
>>> s
('ACME', 50, 91.1)
>>> s[0]
'ACME'
>>> s.name
'ACME'
>>> s.shares * s.price
4555.0

def typed_property(name, expected_type):
    storage_name = '_' + name

    @property
    def prop(self):
        return getattr(self, storage_name)

    @prop.setter
    def prop(self, value):
        if not isinstance(value, expected_type):
            raise TypeError('{} must be a {}'.format(name, expected_type))
        setattr(self, storage_name, value)

    return prop
  
from functools import partial

String = partial(typed_property, expected_type=str)
Integer = partial(typed_property, expected_type=int)

# Example:
class Person:
    name = String('name')
    age = Integer('age')

    def __init__(self, name, age):
        self.name = name
        self.age = age
        

import time
from contextlib import contextmanager

@contextmanager
def timethis(label):
    start = time.time()
    try:
        yield
    finally:
        end = time.time()
        print('{}: {}'.format(label, end - start))

# Example use
with timethis('counting'):
    n = 10000000
    while n > 0:
        n -= 1
        

# 这段代码的作用是任何对列表的修改只有当所有代码运行完成并且不出现异常的情况下才会生效。 
@contextmanager
def list_transaction(orig_list):
    working = list(orig_list)
    yield working
    orig_list[:] = working
    
>>> items = [1, 2, 3]
>>> with list_transaction(items) as working:
...     working.append(4)
...     working.append(5)
...
>>> items
[1, 2, 3, 4, 5]
>>> with list_transaction(items) as working:
...     working.append(6)
...     working.append(7)
...     raise RuntimeError('oops')
...
Traceback (most recent call last):
    File "<stdin>", line 4, in <module>
RuntimeError: oops
>>> items
[1, 2, 3, 4, 5]
>>>

>>> def test4():
...     a = 13
...     loc = { 'a' : a }
...     glb = { }
...     exec('b = a + 1', glb, loc)
...     b = loc['b']
...     print(b)
...
>>> test4()
14
>>>

# somemodule.py
def spam():
    pass

def grok():
    pass

blah = 42
# Only export 'spam' and 'grok'
__all__ = ['spam', 'grok']

# mypackage/A/spam.py
from . import grok

# mypackage/A/spam.py
from ..B import bar

# a.py
class A:
    def spam(self):
        print('A.spam')

# b.py
from .a import A
class B(A):
    def bar(self):
        print('B.bar')

# __init__.py
from .a import A
from .b import B

>>> import mymodule
>>> a = mymodule.A()
>>> a.spam()
A.spam
>>> b = mymodule.B()
>>> b.bar()
B.bar
>>>

>>> import sys
>>> sys.path.extend(['foo-package', 'bar-package'])
>>> import spam.blah
>>> import spam.grok
>>>

>>> import spam
>>> spam.__path__
_NamespacePath(['foo-package/spam', 'bar-package/spam'])
>>> spam.__file__
Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute '__file__'
>>> spam
<module 'spam' (namespace)>
>>>

bash % python3 myapplication

bash % ls
spam.py bar.py grok.py __main__.py
bash % zip -r myapp.zip *.py
bash % python3 myapp.zip
... output from __main__.py ...

# spam.py
import pkgutil
data = pkgutil.get_data(__package__, 'somedata.dat')

import sys
from os.path import abspath, join, dirname
sys.path.insert(0, join(abspath(dirname(__file__)), 'libs'))

>>> import importlib
>>> math = importlib.import_module('math')
>>> math.sin(2)
0.9092974268256817
>>> mod = importlib.import_module('urllib.request')
>>> u = mod.urlopen('http://www.python.org')
>>>

import importlib
# Same as 'from . import b'
b = importlib.import_module('.b', __package__)

python3 setup.py install --user

pip install --user packagename

python3.6 -m venv ./Spam
bash ./Span/bin/activate #进入新的python环境
deactivate #退出新的python环境

# setup.py
from distutils.core import setup

setup(name='projectname',
    version='1.0',
    author='Your Name',
    author_email='you@youraddress.com',
    url='http://www.you.com/projectname',
    packages=['projectname', 'projectname.utils'],
)

% bash python3 setup.py sdist

from urllib import request, parse


# Extra headers
headers = {
    'User-agent' : 'none/ofyourbusiness',
    'Spam' : 'Eggs'
}

# Base URL being accessed
url = 'http://httpbin.org/get'

# Dictionary of query parameters (if any)
parms = {
   'name1' : 'value1',
   'name2' : 'value2'
}

# Encode the query string
querystring = parse.urlencode(parms)

# Make a GET request and read the response
u = request.urlopen(url+'?' + querystring, headers=headers)
resp = u.read()

from urllib import request, parse

# Base URL being accessed
url = 'http://httpbin.org/post'

# Dictionary of query parameters (if any)
parms = {
   'name1' : 'value1',
   'name2' : 'value2'
}

# Encode the query string
querystring = parse.urlencode(parms)

# Make a POST request and read the response
u = request.urlopen(url, querystring.encode('ascii'), headers=headers)
resp = u.read()

import requests

# Base URL being accessed
url = 'http://httpbin.org/post'

# Dictionary of query parameters (if any)
parms = {
   'name1' : 'value1',
   'name2' : 'value2'
}

# Extra headers
headers = {
    'User-agent' : 'none/ofyourbusiness',
    'Spam' : 'Eggs'
}

resp = requests.post(url, data=parms, headers=headers)

# Decoded text returned by the request
text = resp.text

from socketserver import BaseRequestHandler, TCPServer
import traceback

class EchoHandler(BaseRequestHandler):
    # Optional settings (defaults shown)
    timeout = 5                      # Timeout on all socket operations
    rbufsize = -1                    # Read buffer size
    wbufsize = 0                     # Write buffer size
    disable_nagle_algorithm = False  # Sets TCP_NODELAY socket option
    def handle(self):
        print('Got connection from', self.client_address)
        while True:
            msg = self.request.recv(8192)
            if not msg:
                break
            self.request.send(msg)


class EchoTCPServer(TCPServer):

    allow_reuse_address = True

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

    def _serve_forever(self):
        try:
            self.serve_forever()
        except KeyboardInterrupt:
            pass
        except Exception:
            traceback.print_exc()
        finally:
            self.shutdown()

    def serve(self, nworkers=15):
        from concurrent.futures.thread import ThreadPoolExecutor
        with ThreadPoolExecutor(max_workers=nworkers, thread_name_prefix='echo_tcp_server') as executor:
            for _ in range(nworkers):
                executor.submit(lambda : self._serve_forever())
            self._serve_forever()


if __name__ == '__main__':
    serv = EchoTCPServer(('', 20000), EchoHandler)
    serv.serve()

from socketserver import BaseRequestHandler, UDPServer
import time
import traceback

class TimeHandler(BaseRequestHandler):
    def handle(self):
        print('Got connection from', self.client_address)
        # Get message and client socket
        msg, sock = self.request
        resp = time.ctime()
        sock.sendto(resp.encode('ascii'), self.client_address)


class TimeUDPServer(UDPServer):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

    def _serve_forever(self):
        try:
            self.serve_forever()
        except KeyboardInterrupt:
            pass
        except Exception:
            traceback.print_exc()
        finally:
            self.shutdown()

    def serve(self, nworkers=15):
        from concurrent.futures.thread import ThreadPoolExecutor
        with ThreadPoolExecutor(max_workers=nworkers, thread_name_prefix='time_udp_server') as executor:
            for _ in range(nworkers):
                executor.submit(lambda : self._serve_forever())
            self._serve_forever()

if __name__ == '__main__':
    serv = TimeUDPServer(('', 20000), TimeHandler)
    serv.serve()

>>> import ipaddress
>>> net = ipaddress.ip_network('123.45.67.64/27')
>>> net
IPv4Network('123.45.67.64/27')
>>> for a in net:
...     print(a)
...
>>> net6 = ipaddress.ip_network('12:3456:78:90ab:cd:ef01:23:30/125')
>>> net6
IPv6Network('12:3456:78:90ab:cd:ef01:23:30/125')
>>> for a in net6:
...     print(a)
...
>>> net.num_addresses
32
>>> net[0]

IPv4Address('123.45.67.64')
>>> net[1]
IPv4Address('123.45.67.65')
>>> net[-1]
IPv4Address('123.45.67.95')
>>> inet = ipaddress.ip_interface('123.45.67.73/27')
>>> inet.network
IPv4Network('123.45.67.64/27')
>>> inet.ip
IPv4Address('123.45.67.73')
>>>

from xmlrpc.server import SimpleXMLRPCServer
import traceback

class KeyValueServer:
    _rpc_methods_ = ['get', 'set', 'delete', 'exists', 'keys']
    def __init__(self, address):
        self._data = {}
        self._serv = SimpleXMLRPCServer(address, allow_none=True)
        for name in self._rpc_methods_:
            self._serv.register_function(getattr(self, name))

    def get(self, name):
        return self._data[name]

    def set(self, name, value):
        self._data[name] = value

    def delete(self, name):
        del self._data[name]

    def exists(self, name):
        return name in self._data

    def keys(self):
        return list(self._data)

    def serve_forever(self):
        try:
            self._serv.serve_forever()
        except KeyboardInterrupt:
            pass
        except Exception:
            traceback.print_exc()
        finally:
            self._serv.shutdown()

# Example
if __name__ == '__main__':
    serv = KeyValueServer(('', 15000))
    nworkers = 15
    from concurrent.futures.thread import ThreadPoolExecutor
    with ThreadPoolExecutor(max_workers=nworkers, thread_name_prefix='keyvalue_rcp_server') as executor:
        for _ in range(nworkers):
            executor.submit(lambda : serv.serve_forever())
        serv.serve_forever()
    
>>> from xmlrpc.client import ServerProxy
>>> s = ServerProxy('http://localhost:15000', allow_none=True)
>>> s.set('foo', 'bar')
>>> s.set('spam', [1, 2, 3])

from multiprocessing.connection import Listener
import traceback

def echo_client(conn):
    try:
        while True:
            msg = conn.recv()
            conn.send(msg)
    except EOFError:
        print('Connection closed')

def serve_forever(serv):
    try:
        while True:
            client = serv.accept()
            echo_client(client)
    except (KeyboardInterrupt, ConnectionAbortedError):
        pass
    except Exception:
        traceback.print_exc()
    finally:
        serv.close()

if __name__ == '__main__':
    serv = Listener(('', 25000), authkey=b'peekaboo')
    nworkers = 15
    from concurrent.futures.thread import ThreadPoolExecutor
    with ThreadPoolExecutor(max_workers=nworkers, thread_name_prefix='multiprocessing_listener') as executor:
        for _ in range(nworkers):
            executor.submit(serve_forever, serv)
        serve_forever(serv)

>>> from multiprocessing.connection import Client
>>> c = Client(('localhost', 25000), authkey=b'peekaboo')
>>> c.send('hello')
>>> c.recv()
'hello'
>>> c.send(42)
>>> c.recv()
42
>>> c.send([1, 2, 3, 4, 5])
>>> c.recv()
[1, 2, 3, 4, 5]

import hmac
import os

def client_authenticate(connection, secret_key):
    '''
    Authenticate client to a remote service.
    connection represents a network connection.
    secret_key is a key known only to both client/server.
    '''
    message = connection.recv(32)
    hash = hmac.new(secret_key, message)
    digest = hash.digest()
    connection.send(digest)

def server_authenticate(connection, secret_key):
    '''
    Request client authentication.
    '''
    message = os.urandom(32)
    connection.send(message)
    hash = hmac.new(secret_key, message)
    digest = hash.digest()
    response = connection.recv(len(digest))
    return hmac.compare_digest(digest,response)
  
from socket import socket, AF_INET, SOCK_STREAM

secret_key = b'peekaboo'
def echo_handler(client_sock):
    if not server_authenticate(client_sock, secret_key):
        client_sock.close()
        return
    while True:

        msg = client_sock.recv(8192)
        if not msg:
            break
        client_sock.sendall(msg)
        

from socket import socket, AF_INET, SOCK_STREAM
secret_key = b'peekaboo'
s = socket(AF_INET, SOCK_STREAM)
s.connect(('localhost', 18000))
client_authenticate(s, secret_key)
s.send(b'Hello World')
resp = s.recv(1024)

import ssl

class SSLMixin:
'''
Mixin class that adds support for SSL to existing servers based
on the socketserver module.
'''
def __init__(self, *args,
             keyfile=None, certfile=None, ca_certs=None,
             cert_reqs=ssl.CERT_NONE,
             **kwargs):
    self._keyfile = keyfile
    self._certfile = certfile
    self._ca_certs = ca_certs
    self._cert_reqs = cert_reqs
    super().__init__(*args, **kwargs)

def get_request(self):
    client, addr = super().get_request()
    client_ssl = ssl.wrap_socket(client,
                                 keyfile = self._keyfile,
                                 certfile = self._certfile,
                                 ca_certs = self._ca_certs,
                                 cert_reqs = self._cert_reqs,
                                 server_side = True)
    return client_ssl, addr
  
class SSLSimpleXMLRPCServer(SSLMixin, SimpleXMLRPCServer):
    pass
  
if __name__ == '__main__':
    KEYFILE='server_key.pem'    # Private key of the server
    CERTFILE='server_cert.pem'  # Server certificate
    kvserv = KeyValueServer(('', 15000),
                            keyfile=KEYFILE,
                            certfile=CERTFILE)
    kvserv.serve_forever()

class EventHandler:
    def fileno(self):
        'Return the associated file descriptor'
        raise NotImplemented('must implement')

    def wants_to_receive(self):
        'Return True if receiving is allowed'
        return False

    def handle_receive(self):
        'Perform the receive operation'
        pass

    def wants_to_send(self):
        'Return True if sending is requested'
        return False

    def handle_send(self):
        'Send outgoing data'
        pass
 
import select

def event_loop(handlers):
    while True:
        wants_recv = [h for h in handlers if h.wants_to_receive()]
        wants_send = [h for h in handlers if h.wants_to_send()]
        can_recv, can_send, _ = select.select(wants_recv, wants_send, [])
        for h in can_recv:
            h.handle_receive()
        for h in can_send:
            h.handle_send()

import socket
import time

class UDPServer(EventHandler):
    def __init__(self, address):
        self.sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
        self.sock.bind(address)

    def fileno(self):
        return self.sock.fileno()

    def wants_to_receive(self):
        return True

class UDPTimeServer(UDPServer):
    def handle_receive(self):
        msg, addr = self.sock.recvfrom(1)
        self.sock.sendto(time.ctime().encode('ascii'), addr)

class UDPEchoServer(UDPServer):
    def handle_receive(self):
        msg, addr = self.sock.recvfrom(8192)
        self.sock.sendto(msg, addr)

if __name__ == '__main__':
    handlers = [ UDPTimeServer(('',14000)), UDPEchoServer(('',15000))  ]
    event_loop(handlers)

class TCPServer(EventHandler):
    def __init__(self, address, client_handler, handler_list):
        self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, True)
        self.sock.bind(address)
        self.sock.listen(1)
        self.client_handler = client_handler
        self.handler_list = handler_list

    def fileno(self):
        return self.sock.fileno()

    def wants_to_receive(self):
        return True

    def handle_receive(self):
        client, addr = self.sock.accept()
        # Add the client to the event loop's handler list
        self.handler_list.append(self.client_handler(client, self.handler_list))

class TCPClient(EventHandler):
    def __init__(self, sock, handler_list):
        self.sock = sock
        self.handler_list = handler_list
        self.outgoing = bytearray()

    def fileno(self):
        return self.sock.fileno()

    def close(self):
        self.sock.close()
        # Remove myself from the event loop's handler list
        self.handler_list.remove(self)

    def wants_to_send(self):
        return True if self.outgoing else False

    def handle_send(self):
        nsent = self.sock.send(self.outgoing)
        self.outgoing = self.outgoing[nsent:]

class TCPEchoClient(TCPClient):
    def wants_to_receive(self):
        return True

    def handle_receive(self):
        data = self.sock.recv(8192)
        if not data:
            self.close()
        else:
            self.outgoing.extend(data)

if __name__ == '__main__':
   handlers = []
   handlers.append(TCPServer(('',16000), TCPEchoClient, handlers))
   event_loop(handlers)

from concurrent.futures import ThreadPoolExecutor
import os

class ThreadPoolHandler(EventHandler):
    def __init__(self, nworkers):
        if os.name == 'posix':
            self.signal_done_sock, self.done_sock = socket.socketpair()
        else:
            server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            server.bind(('127.0.0.1', 0))
            server.listen(1)
            self.signal_done_sock = socket.socket(socket.AF_INET,
                                                  socket.SOCK_STREAM)
            self.signal_done_sock.connect(server.getsockname())
            self.done_sock, _ = server.accept()
            server.close()

        self.pending = []
        self.pool = ThreadPoolExecutor(nworkers)

    def fileno(self):
        return self.done_sock.fileno()

    # Callback that executes when the thread is done
    def _complete(self, callback, r):

        self.pending.append((callback, r.result()))
        self.signal_done_sock.send(b'x')

    # Run a function in a thread pool
    def run(self, func, args=(), kwargs={},*,callback):
        r = self.pool.submit(func, *args, **kwargs)
        r.add_done_callback(lambda r: self._complete(callback, r))

    def wants_to_receive(self):
        return True

    # Run callback functions of completed work
    def handle_receive(self):
        # Invoke all pending callback functions
        for callback, result in self.pending:
            callback(result)
            self.done_sock.recv(1)
        self.pending = []
        
# A really bad Fibonacci implementation
def fib(n):
    if n < 2:
        return 1
    else:
        return fib(n - 1) + fib(n - 2)

class UDPFibServer(UDPServer):
    def handle_receive(self):
        msg, addr = self.sock.recvfrom(128)
        n = int(msg)
        pool.run(fib, (n,), callback=lambda r: self.respond(r, addr))

    def respond(self, result, addr):
        self.sock.sendto(str(result).encode('ascii'), addr)

if __name__ == '__main__':
    pool = ThreadPoolHandler(16)
    handlers = [ pool, UDPFibServer(('',16000))]
    event_loop(handlers)