PythonEngineer/index.html at master · lydgithub/PythonEngineer · GitHub

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<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>后端那些事</title>
    <link rel="stylesheet" href="css/default.css" media="screen">
  </head>
  <body>
    <textarea id="source">

class: middle, inverse, center
#后端那些事

### yihaibo
2015.12.29

---

# 后端研究什么

##总结：4个一

- 语言(python)

- 操作系统(linux)

- 存储(mysql)

- 领域(web, 数据分析，web安全，密码技术)

---

# 语言
一.静态语言，动态语言，弱类型语言，强类型语言

- 区别

- 举例

    Python是动态强类型语言

    Golang是静态强类型语言

    C是静态弱类型语言

- 反射(自省)

---

二.并发与并行

- 区别

- 举例

    Erlang, Golang是天生支持并行的

    Python由于GIL限制单进程只能并发

---

三.Python

- 数据类型, 数据结构

- 推导式与函数式

- 算法

- 反射

- 属性拦截

- 装饰器

- 描述符和属性

- 生成器

- 元类

- 垃圾回收

- 多线程与多进程

- 其它


---
###数据类型
所有数据类型都是对象
```
# 64位操作系统
In [40]: sys.getsizeof(1)
Out[40]: 24
In [41]: sys.getsizeof(1L)
Out[41]: 28
In [42]: sys.getsizeof("")
Out[42]: 37
In [43]: sys.getsizeof("hello")
Out[43]: 42
In [44]: sys.getsizeof([])
Out[44]: 72
In [45]: sys.getsizeof([1])
Out[45]: 80

```
---
class: middle
####什么时候2+2==5?
```
In [50]: 2+2
Out[50]: 4

In [51]: ctypes.memmove(id(4), id(5), 24)
Out[51]: 11637008

In [52]: 2+2
Out[52]: 5

In [53]: 4
Out[53]: 5

```
---
###数据结构

- list, tuple, dict, set

- collection.namedtuple, collection.deque, collection.OrderedDict, collections.defaultdict

- Queue.Queue

```
Person=collections.namedtuple('Person','name age gender')

p=Person("kehan", 2, "female")

p.name
Out[12]: 'kehan'

```
####思考 底层原理？？？
---
- 可变与不可变

```
In [1]: def test(gameids=[1,2]):
   ...:     gameids.append(3)
   ...:     print(gameids)
In [2]: test()
[1, 2, 3]
In [3]: test()
[1, 2, 3, 3]
In [4]: test.func_defaults
Out[4]: ([1, 2, 3, 3],)
```
```
In [18]: a={}
In [19]: b=[]
In [20]: a[b]=1
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-20-2bfc1dd9a880> in <module>()
----> 1 a[b]=1

TypeError: unhashable type: 'list'
```
---
class: middle
```
persons = {}

class Person(object):
    def __init__(self, name):
        self.name = name

    def __hash__(self):
        return hash(self.name)

persons[Person("kehan")] = 1
print(Person("kehan") in persons) #False
```
---
class: middle
```
persons = {}

class Person(object):
    def __init__(self, name):
        self.name = name

    def __hash__(self):
        return hash(self.name)

    def __eq__(self, r):
        return True if r.name == self.name else False


persons[Person("kehan")] = 1
print(Person("kehan") in persons) #True
```
---
### 推导式与函数式

comprehension: list, dict, set

函数式: map, filter, reduce等

```python
t_columns = filter(lambda x: x.endswith("_time"),
        model.FIELDS)

t_columns = [f for f in model.FIELDS
            if f.endswith("_time")]

# 小于0置为0
ages = [-1, 10, 20]

sum([age if age >=0 else 0 for age in ages ])

sum(age if age >=0 else 0 for age in ages)  # 生成器

sum(map(lambda age: age if age >=0 else 0, ages))

```

---
###算法

####排序

```
peoples = [
    {"age": 1, "name": "kehan"},
    {"age": 24, "name": "lwy"},
    {"age": 25, "name": "skycrab"},
]
# age从小到大,
sorted(peoples, key=lambda p:p["age"])
# 从大到小
sorted(peoples, key=operator.itemgetter("age"),
    reverse=True)

operator.attrgetter     # 属性
operator.itemgetter     #元素
operator.methodcaller   #方法
```
---
class: middle
```
#最大age
max(peoples, key=operator.itemgetter("age"))
{'age': 25, 'name': 'skycrab'}

min(peoples, key=operator.itemgetter("age"))
{'age': 25, 'name': 'skycrab'}

# operator模块是一个宝藏
a = [1, 2, 3]
reduce(operator.imul, a)  # 6

reduce(lambda x, y: x+y, a)  # 6

```
---

####二分查找
前提: 已排序数列

```
a=[1, 5, 10, 15,20]

# bisect.bisect_right(a, x) 返回a中插入x的序号
bisect.bisect_right(a, 11)
Out[11]: 3

bisect.insort_right(a,11)

In [13]: a
Out[13]: [1, 5, 10, 11, 15, 20]

```

---
###堆排序
解决TOP N问题

```
# heapq是最小堆

a=[1]

heapq.heappush(a, 10) # a=[1, 10]
heapq.heappop(a)      #弹出1

heapq.nlargest(2, peoples,
    key=operator.itemgetter("age"))

[{'age': 25, 'name': 'skycrab'}, {'age': 24, 'name': 'lwy'}]

```

---
###反射(自省)

- getattr, setattr,  hasattr, dir

- \_\_dict\_\_, \_\_slots\_\_

- callable, isinstance

- traceback

- inspect

好处是什么？？？

- orm

---
class:inverse
```
In [13]: class Person(object):
   ....:     desc = "person object"
   ....:     def __init__(self):
   ....:         self.age = 100

   In [14]: Person.__dict__
   Out[14]:
   <dictproxy {'__dict__': <attribute '__dict__' of 'Person' objects>,
   '__doc__': None,
   '__init__': <function __main__.__init__>,
   '__module__': '__main__',
   '__weakref__': <attribute '__weakref__' of 'Person' objects>,
   'desc': 'person object'}>

   In [15]: p=Person()
   In [16]: p.__dict__
   Out[16]: {'age': 100}
   In [22]: hasattr(p, "age")
   Out[22]: True
   In [23]: getattr(p, "desc")
   Out[23]: 'person object'

 ```
---
class:inverse
```
class Point(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y

In [24]: P=Point(1,1)
In [28]: P.__dict__
Out[28]: {'x': 1, 'y': 1}
In [38]: P.age=100

class EPoint(object):
    __slots__ = ("x","y")
    def __init__(self, x, y):
        self.x = x
        self.y = y

In [33]: Ep=EPoint(1,1)
In [35]: Ep.__dict__
AttributeError: 'EPoint' object has no attribute '__dict__'
In [39]: Ep.age=100
AttributeError: 'EPoint' object has no attribute 'age'

```
---
class:inverse
```
In [26]: isinstance(p, Person)
Out[26]: True
In [29]: callable(os.path.join)
Out[29]: True
In [33]: class FunCall(object):
            def __call__(self, *args, **kwargs):
                print(args, kwargs)

In [34]: f=FunCall()
In [35]: callable(f)
Out[35]: True
In [36]: f("hello", name="funcall")
(('hello',), {'name': 'funcall'})

In [10]: try:
   ....:     1/0
   ....: except Exception:
   ....:     print(traceback.format_exc())
   ....:
   .........ZeroDivisionError: integer division or modulo by zero

```

---

###属性拦截

```
# dataeye/statistics/bi/sdkincome.py
class Merge(object):
    ""获取django多个结果""
    def __init__(self, query_set):
        self.query_set = query_set
    def __getattr__(self, name):
        return sum(getattr(q, name)
            for q in self.query_set)

class ObjectDict(dict):
    """字典当做对象使用"""
    def __getattr__(self, name):
        try:
            return self[name]
        except KeyError:
            raise AttributeError(name)
    def __setattr__(self, name, value):
        self[name] = value
```
---

```
# dataeye/statistics/context_processors.py

class PermWrapper(object):
    def __init__(self, user):
        self.user = user
        self.superuser = user.is_superuser
        self.perms = set(["101", "102"])

    def __getitem__(self, module_name):
        if hasattr(self, module_name):
            return getattr(self, module_name)

        return module_name in self.perms

perm = PermWrapper()
perm["superuser"]
perm["101"]

```
---
###装饰器
- 闭包

- 好处,　解耦

- 面向切面编程(aop)

- 用处(日志记录，权限控制，事物处理等)

- 分类(不带参数，带参数，类装饰器)

```
cf = ConfigParser.ConfigParser()
cf.read("config.ini")
get = functools.partial(cf.get, "analyse")
cf.get("analyse", "host")
print(get("host"), get("db"), get("user"))

```
---
```
def XXX(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        # before hook
        return func(*args, **kwargs)
        # after hook
    return wrapper


def super_required(view_func):
    """超级用户控制"""
    @wraps(view_func)
    def decorator(request, *args, **kwargs):
        if request.user.is_authenticated()
            and request.user.is_superuser:
            return view_func(request,*args,**kwargs)
        else:
            return HttpResponseRedirect("/login/
               ?next= {0}".format(request.path))
    return decorator
```

---
需求：使用torndb，记录执行的sql语句和执行时间

属性拦截与装饰器结合
```
# analyse/script/fabfile.py  简化
def log(level):
    """记录日志"""
    assert level in ("debug", "info", "warn", "error")
    def decorator(func):
        @wraps(func)
        def wrapper(*args, **kwargs):
            start = time.time()
            result = func(*args, **kwargs)
            write = getattr(logger, level)
            write("sql: %s\nrun time: %s seconds",
                args, time.time()-start)
            return result
        return wrapper
    return decorator
```
---
```
# analyse/script/fabfile.py
class Connection(object):
    def __init__(self):
        self.conn = torndb.Connection(HOST, DB, USER, PASSWORED)

    def __getattr__(self, name):
        func = getattr(self.conn, name)
        return log("info")(func)

conn = Connection()
conn.get("select * from manage_ana_app where id=7")
conn.execute("delete * from manage_ana_app")

sql: select * from manage_ana_app where id=7
run time: 0.5111111 seconds

```
---
### 描述符和属性

- 作用: 覆盖默认属性查找方式

    a.x -> a.\_\_dict\_\_['x'] ->type(a).\_\_dict\_\_['x'] -> baseclass(type(a)).\_\_dict\_\_['x']

- \_\_get\_\_, \_\_set\_\_, \_\_delete\_\_

    数据描述符: \_\_get\_\_, \_\_set\_\_  (描述符优先)

    非数据描述符: \_\_get\_\_  (\_\_dict\_\_优先)

- 只支持new style objects

    描述符是由\_\_getattribute\_\_调用，只在新式类中才有

- properties, methods, statis methods, class methods, super

- classmethod实现原理

详细参考:  https://docs.python.org/2/howto/descriptor.html?highlight=descriptor

---
class: middle
```
#非数据描述符

class descriptor(object):
    def __init__(self, value):
        self.value = value

    def __get__(self, obj, type=None):
        print obj, type
        return self.value

class Test(object):
    def __init__(self):
        self.age = 100

    age = descriptor(200)


t= Test()
print(t.age)  # 100

```
---
```
#数据描述符

class descriptor(object):
    def __init__(self, value):
        self.value = value

    def __get__(self, obj, type=None):
        return self.value

    def __set__(self, obj, value):
        pass

class Test(object):
    def __init__(self):
        self.age = 100

    age = descriptor(200)


t= Test()
print(t.age) # 200
```
---
class: middle
ClassMethod实现原理
```
class ClassMethod(object):
     "Emulate PyClassMethod_Type() in Objects/funcobject.c"

     def __init__(self, f):
          self.f = f

     def __get__(self, obj, klass=None):
          if klass is None:
               klass = type(obj)
          def newfunc(*args):
               return self.f(klass, *args)
          return newfunc
```
---
```
# analyse/bi/util.py
class class_property(object):
    """ A property can decorator class or instance
    class Foo(object):
        @class_property
        def foo(cls):
            return 42
    print(Foo.foo)
    print(Foo().foo)

    """
    def __init__(self, func, name=None, doc=None):
        self.__name__ = name or func.__name__
        self.__module__ = func.__module__
        self.__doc__ == doc or func.__doc__
        self.func = func

    def __get__(self, obj, type=None):
        value = self.func(type)
        return value
```
---
class:middle, inverse
```
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.
        class Foo(object):
            @cached_property
            def foo(self):
                return 42*100*100
        print(Foo().foo)

    """

    def __init__(self, func):
        self.__doc__ = getattr(func, '__doc__')
        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:middle
```
class class_cached_property(object):

    def __init__(self, func):
        self.__doc__ = getattr(func, '__doc__')
        self.func = func

    def __get__(self, obj, cls):
        if cls is None:
            return self
        value = self.func(cls)
        setattr(cls, self.func.__name__, value)
        return value
```
---
###生成器
```
In [2]: g=(2*x for x in range(2))

In [3]: g
Out[3]: <generator object <genexpr> at 0x00000000043E6630>

In [4]: g.next()
Out[4]: 0

In [5]: g.next()
Out[5]: 2

In [6]: g.next()
---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
<ipython-input-6-d7e53364a9a7> in <module>()
----> 1 g.next()

StopIteration:

```
---
```
In [12]: def task():
   ....:     for x in range(2):
   ....:         yield x
   ....:
In [13]: t=task()

In [14]: t
Out[14]: <generator object task at 0x00000000035F9558>
In [15]: print(t.next())
0
In [16]: print(t.next())
1
In [17]: print(t.next())
---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
<ipython-input-19-487d3bab2781> in <module>()
----> 1 print(t.next())
StopIteration:
```
---
class: middle
```
def task():
    begin = yield
    print("begin",begin)
    yield
    for x in range(begin):
        yield x

t = task()
t.send(None)
t.send(2)
print([x for x in t])

result:
('begin', 2)
[0, 1]
```
---
```
def thread1():
    for x in range(4):
        yield  x


def thread2():
    for x in range(4,8):
        yield  x


threads=[]
threads.append(thread1())
threads.append(thread2())


def run(threads): #写这个函数，模拟线程并发
    pass

run(threads)
```
---
class:middle
```
def run(threads): #写这个函数，模拟线程并发
    for t in threads:
        try:
            print t.next()
        except StopIteration:
            pass
        else:
            threads.append(t)
结果：
0
4
1
5
2
6
3
7
```
---
class:inverse
```
class Task(object):
    def __init__(self):
        self._queue = collections.deque()
        self.work = 0
    def add(self, gen):
        self._queue.append(gen)
        self.work += 1
    def finish(self):
        return self.work <= 0
    def run(self):
        while not self.finish():
            try:
                gen = self._queue.popleft()
                gen.send(None)
            except StopIteration:
                self.work -= 1
            else:
                self._queue.append(gen)
t=Task()
t.add(thread1())  t.add(thread2())
t.run()
```
---
###上下文管理器

####with 协议
```
class cd(object):
    def __init__(self, path):
        self.src = os.getcwd()
        self.dest = path

    def __enter__(self):
        os.chdir(self.dest)

    def __exit__(self, exc_type, exc_val, exc_tb):
        """返回True忽略异常"""
        os.chdir(self.src)

```
---
class: middle
```
from contextlib import contextmanager

@contextmanager
def cd(path):
    cwd = os.getcwd()
    try:
        os.chdir(path)
        yield
    finally:
        os.chdir(cwd)
```
---
###元类
- type

```
In [25]: class A(object):
   ....:     pass
   ....:

In [26]: type(A)
Out[26]: type

In [27]: B = type("B", (object,), {"name":"BBB"})

In [28]: B
Out[28]: __main__.B

In [30]: B.name
Out[30]: 'BBB'
```
---
- \_\_new\_\_(cls, classname, bases, dict_attr)
- \_\_init\_\_(cls, classname, bases, dict_attr)

注意：

- \_\_new\_\_的cls参数是元类自己

- \_\_init\_\_的cls参数是元类创建的那个类


```
_extract = {}
_site = re.compile(r".*\.(?P<site>.+?)\.com")
def parse(url):
    """解析视频真实地址"""
    site = _site.search(url).group('site')
    parser = _extract[site]
    return parser.parse(url)

parse("http://www.letv.com/ptv/vplay/1111.html")
```
---
```
class VideoMeta(type):
    def __init__(cls, classname, bases, dict_attr):
        """注意这里是cls, 如Video, LeTv"""
        assert hasattr(cls, "parse")
        assert hasattr(cls, "NAME")
        _extract[dict_attr["NAME"]] = cls()
        return type.__init__(cls, classname, bases, dict_attr)

class Video(object):
    __metaclass__ = VideoMeta
    NAME = "BASE"
    def parse(self, url):
        raise NotImplementedError

class LeTv(Video):
    """乐视TV"""
    NAME = "letv"
    def parse(self, url):
        pass

```
---
class: middle
```
class UpperMeta(type):
    """将属性修改为大写, 只能是__new__"""
    def __new__(cls, classname, bases, dict_attr):
        attr = {k.upper() if not k.startswith("__") else
            k : v for k,v in dict_attr.items()}
        return type.__new__(cls, classname, bases, attr)


class Person(object):
    __metaclass__ = UpperMeta
    name = "lwy"
    age = 24

print( "name" in Person.__dict__) #False
print( "NAME" in Person.__dict__) #True
```
---
###垃圾回收
引用计数为主，标记-清除和分代收集为辅
```
In [33]: class A(object):
   ....:     pass
   ....:
In [34]: a=A()

In [36]: sys.getrefcount(a)
Out[36]: 2

In [37]: sys.getrefcount?
Return the reference count of object.  The count returned is generally
one higher than you might expect, because it includes the (temporary)
reference as an argument to getrefcount().

In [38]: b=a

In [39]: sys.getrefcount(a)
Out[39]: 3

```
---
引用计数

- 优点
    简单, 实时

- 缺点
    吞吐量不高, 循环引用

标记-清除：
```
gc.set_debug(gc.DEBUG_STATS)

a = []
b = []
a.append(b)
b.append(a)
del a
del b
print("unreachable:", gc.collect())

gc: collecting generation 2...
gc: objects in each generation: 504 3398 0
gc: done, 2 unreachable, 0 uncollectable, 0.0010s elapsed.
('unreachable:', 2)
```
---
class:middle
```
# 没有不可达对象,靠引用计数就可以

gc.set_debug(gc.DEBUG_STATS)

a = []
b = []
a.append(b)
b.append(a)
del a
print("unreachable:", gc.collect())

gc: collecting generation 2...
gc: objects in each generation: 504 3398 0
gc: done, 0.0010s elapsed.
('unreachable:', 0)
```

---
- gc.enable()