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python實用代碼片段收集貼

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獲取一個類的所有子類

復(fù)制代碼 代碼如下:

def itersubclasses(cls, _seen=None):
??? """Generator over all subclasses of a given class in depth first order."""
??? if not isinstance(cls, type):
??????? raise TypeError(_('itersubclasses must be called with '
????????????????????????? 'new-style classes, not %.100r') % cls)
??? _seen = _seen or set()
??? try:
??????? subs = cls.__subclasses__()
??? except TypeError:?? # fails only when cls is type
??????? subs = cls.__subclasses__(cls)
??? for sub in subs:
??????? if sub not in _seen:
??????????? _seen.add(sub)
??????????? yield sub
??????????? for sub in itersubclasses(sub, _seen):
??????????????? yield sub

簡單的線程配合

復(fù)制代碼 代碼如下:

import threading
is_done = threading.Event()
consumer = threading.Thread(
??? target=self.consume_results,
??? args=(key, self.task, runner.result_queue, is_done))
consumer.start()
self.duration = runner.run(
??????? name, kw.get("context", {}), kw.get("args", {}))
is_done.set()
consumer.join() #主線程堵塞,直到consumer運行結(jié)束

多說一點,threading.Event()也可以被替換為threading.Condition(),condition有notify(), wait(), notifyAll()。解釋如下:
復(fù)制代碼 代碼如下:

The wait() method releases the lock, and then blocks until it is awakened by a notify() or notifyAll() call for the same condition variable in another thread. Once awakened, it re-acquires the lock and returns. It is also possible to specify a timeout.
The notify() method wakes up one of the threads waiting for the condition variable, if any are waiting. The notifyAll() method wakes up all threads waiting for the condition variable.
Note: the notify() and notifyAll() methods don't release the lock; this means that the thread or threads awakened will not return from their wait() call immediately, but only when the thread that called notify() or notifyAll() finally relinquishes ownership of the lock.

復(fù)制代碼 代碼如下:

# Consume one item
cv.acquire()
while not an_item_is_available():
??? cv.wait()
get_an_available_item()
cv.release()
# Produce one item
cv.acquire()
make_an_item_available()
cv.notify()
cv.release()

計算運行時間

復(fù)制代碼 代碼如下:

class Timer(object):
??? def __enter__(self):
??????? self.error = None
??????? self.start = time.time()
??????? return self
??? def __exit__(self, type, value, tb):
??????? self.finish = time.time()
??????? if type:
??????????? self.error = (type, value, tb)
??? def duration(self):
??????? return self.finish - self.start
with Timer() as timer:
??? func()
return timer.duration()

元類

__new__()方法接收到的參數(shù)依次是:
當前準備創(chuàng)建的類的對象;
類的名字;
類繼承的父類集合;
類的方法集合;

復(fù)制代碼 代碼如下:

class ModelMetaclass(type):
??? def __new__(cls, name, bases, attrs):
??????? if name=='Model':
??????????? return type.__new__(cls, name, bases, attrs)
??????? mappings = dict()
??????? for k, v in attrs.iteritems():
??????????? if isinstance(v, Field):
??????????????? print('Found mapping: %s==>%s' % (k, v))
??????????????? mappings[k] = v
??????? for k in mappings.iterkeys():
??????????? attrs.pop(k)
??????? attrs['__table__'] = name # 假設(shè)表名和類名一致
??????? attrs['__mappings__'] = mappings # 保存屬性和列的映射關(guān)系
??????? return type.__new__(cls, name, bases, attrs)
class Model(dict):
??? __metaclass__ = ModelMetaclass
??? def __init__(self, **kw):
??????? super(Model, self).__init__(**kw)
??? def __getattr__(self, key):
??????? try:
??????????? return self[key]
??????? except KeyError:
??????????? raise AttributeError(r"'Model' object has no attribute '%s'" % key)
??? def __setattr__(self, key, value):
??????? self[key] = value
??? def save(self):
??????? fields = []
??????? params = []
??????? args = []
??????? for k, v in self.__mappings__.iteritems():
??????????? fields.append(v.name)
??????????? params.append('?')
??????????? args.append(getattr(self, k, None))
??????? sql = 'insert into %s (%s) values (%s)' % (self.__table__, ','.join(fields), ','.join(params))
??????? print('SQL: %s' % sql)
??????? print('ARGS: %s' % str(args))
class Field(object):
??? def __init__(self, name, column_type):
??????? self.name = name
??????? self.column_type = column_type
??? def __str__(self):
??????? return '<%s:%s>' % (self.__class__.__name__, self.name)
class StringField(Field):
??? def __init__(self, name):
??????? super(StringField, self).__init__(name, 'varchar(100)')
class IntegerField(Field):
??? def __init__(self, name):
??????? super(IntegerField, self).__init__(name, 'bigint')
class User(Model):
??? # 定義類的屬性到列的映射:
??? id = IntegerField('id')
??? name = StringField('username')
??? email = StringField('email')
??? password = StringField('password')
# 創(chuàng)建一個實例:
u = User(id=12345, name='Michael', email='test@orm.org', password='my-pwd')
# 保存到數(shù)據(jù)庫:
u.save()

輸出如下:

復(fù)制代碼 代碼如下:

Found model: User
Found mapping: email ==>
Found mapping: password ==>
Found mapping: id ==>
Found mapping: name ==>
SQL: insert into User (password,email,username,uid) values (?,?,?,?)
ARGS: ['my-pwd', 'test@orm.org', 'Michael', 12345]

SQLAlchemy簡單使用

復(fù)制代碼 代碼如下:

# 導(dǎo)入:
from sqlalchemy import Column, String, create_engine
from sqlalchemy.orm import sessionmaker
from sqlalchemy.ext.declarative import declarative_base
# 創(chuàng)建對象的基類:
Base = declarative_base()
# 定義User對象:
class User(Base):
??? # 表的名字:
??? __tablename__ = 'user'
??? # 表的結(jié)構(gòu):
??? id = Column(String(20), primary_key=True)
??? name = Column(String(20))
# 初始化數(shù)據(jù)庫連接:
engine = create_engine('mysql+mysqlconnector://root:password@localhost:3306/test') # '數(shù)據(jù)庫類型+數(shù)據(jù)庫驅(qū)動名稱://用戶名:口令@機器地址:端口號/數(shù)據(jù)庫名'
# 創(chuàng)建DBSession類型:
DBSession = sessionmaker(bind=engine)
# 創(chuàng)建新User對象:
new_user = User(id='5', name='Bob')
# 添加到session:
session.add(new_user)
# 提交即保存到數(shù)據(jù)庫:
session.commit()
# 創(chuàng)建Query查詢,filter是where條件,最后調(diào)用one()返回唯一行,如果調(diào)用all()則返回所有行:
user = session.query(User).filter(User.id=='5').one()
# 關(guān)閉session:
session.close()

WSGI簡單使用和Web框架Flask的簡單使用

復(fù)制代碼 代碼如下:

from wsgiref.simple_server import make_server
def application(environ, start_response):
??? start_response('200 OK', [('Content-Type', 'text/html')])
??? return '

Hello, web!

'
# 創(chuàng)建一個服務(wù)器,IP地址為空,端口是8000,處理函數(shù)是application:
httpd = make_server('', 8000, application)
print "Serving HTTP on port 8000..."
# 開始監(jiān)聽HTTP請求:
httpd.serve_forever()

了解了WSGI框架,我們發(fā)現(xiàn):其實一個Web App,就是寫一個WSGI的處理函數(shù),針對每個HTTP請求進行響應(yīng)。
但是如何處理HTTP請求不是問題,問題是如何處理100個不同的URL。
一個最簡單和最土的想法是從environ變量里取出HTTP請求的信息,然后逐個判斷。

復(fù)制代碼 代碼如下:

from flask import Flask
from flask import request
app = Flask(__name__)
@app.route('/', methods=['GET', 'POST'])
def home():
??? return '

Home

'
@app.route('/signin', methods=['GET'])
def signin_form():
??? return '''

?????????????


?????????????


?????????????


?????????????
'''
@app.route('/signin', methods=['POST'])
def signin():
??? # 需要從request對象讀取表單內(nèi)容:
??? if request.form['username']=='admin' and request.form['password']=='password':
??????? return '

Hello, admin!

'
??? return '

Bad username or password.

'
if __name__ == '__main__':
??? app.run()

格式化顯示json

復(fù)制代碼 代碼如下:

print(json.dumps(data, indent=4))
# 或者
import pprint
pprint.pprint(data)

實現(xiàn)類似Java或C中的枚舉

復(fù)制代碼 代碼如下:

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import itertools
import sys
class ImmutableMixin(object):
??? _inited = False
??? def __init__(self):
??????? self._inited = True
??? def __setattr__(self, key, value):
??????? if self._inited:
??????????? raise Exception("unsupported action")
??????? super(ImmutableMixin, self).__setattr__(key, value)
class EnumMixin(object):
??? def __iter__(self):
??????? for k, v in itertools.imap(lambda x: (x, getattr(self, x)), dir(self)):
??????????? if not k.startswith('_'):
??????????????? yield v
class _RunnerType(ImmutableMixin, EnumMixin):
??? SERIAL = "serial"
??? CONSTANT = "constant"
??? CONSTANT_FOR_DURATION = "constant_for_duration"
??? RPS = "rps"
if __name__=="__main__":
??? print _RunnerType.CONSTANT

創(chuàng)建文件時指定權(quán)限

復(fù)制代碼 代碼如下:

import os
def write_to_file(path, contents, umask=None):
??? """Write the given contents to a file
??? :param path: Destination file
??? :param contents: Desired contents of the file
??? :param umask: Umask to set when creating this file (will be reset)
??? """
??? if umask:
??????? saved_umask = os.umask(umask)
??? try:
??????? with open(path, 'w') as f:
??????????? f.write(contents)
??? finally:
??????? if umask:
??????????? os.umask(saved_umask)
if __name__ == '__main__':
??? write_to_file('/home/kong/tmp', 'test', 31)
??? # Then you will see a file is created with permission 640.
??? # Warning: If the file already exists, its permission will not be changed.
??? # Note:For file, default all permission is 666, and 777 for directory.

多進程并發(fā)執(zhí)行

復(fù)制代碼 代碼如下:

import multiprocessing
import time
import os
def run(flag):
??? print "flag: %s, sleep 2s in run" % flag
??? time.sleep(2)
??? print "%s exist" % flag
??? return flag
if __name__ == '__main__':
??? pool = multiprocessing.Pool(3)
??? iter_result = pool.imap(run, xrange(6))
??? print "sleep 5s\n\n"
??? time.sleep(5)
??? for i in range(6):
??????? try:
??????????? result = iter_result.next(600)
??????? except multiprocessing.TimeoutError as e:
??????????? raise
??????? print result
??? pool.close()
??? pool.join()

運行時自動填充函數(shù)參數(shù)

復(fù)制代碼 代碼如下:

import decorator
def default_from_global(arg_name, env_name):
??? def default_from_global(f, *args, **kwargs):
??????? id_arg_index = f.func_code.co_varnames.index(arg_name)
??????? args = list(args)
??????? if args[id_arg_index] is None:
??????????? args[id_arg_index] = get_global(env_name)
??????????? if not args[id_arg_index]:
??????????????? print("Missing argument: --%(arg_name)s" % {"arg_name": arg_name})
??????????????? return(1)
??????? return f(*args, **kwargs)
??? return decorator.decorator(default_from_global)
# 如下是一個裝飾器,可以用在需要自動填充參數(shù)的函數(shù)上。功能是:
# 如果沒有傳遞函數(shù)的deploy_id參數(shù),那么就從環(huán)境變量中獲取(調(diào)用自定義的get_global函數(shù))
with_default_deploy_id = default_from_global('deploy_id', ENV_DEPLOYMENT)???

嵌套裝飾器

validator函數(shù)裝飾func1,func1使用時接收參數(shù)(*arg, **kwargs),而func1又裝飾func2(其實就是Rally中的scenario函數(shù)),給func2增加validators屬性,是一個函數(shù)的列表,函數(shù)的接收參數(shù)config, clients, task。這些函數(shù)最終調(diào)用func1,傳入?yún)?shù)(config, clients, task, *args, **kwargs),所以func1定義時參數(shù)是(config, clients, task, *arg, **kwargs)?
最終實現(xiàn)的效果是,func2有很多裝飾器,每個都會接收自己的參數(shù),做一些校驗工作。

復(fù)制代碼 代碼如下:

def validator(fn):
??? """Decorator that constructs a scenario validator from given function.
??? Decorated function should return ValidationResult on error.
??? :param fn: function that performs validation
??? :returns: rally scenario validator
??? """
??? def wrap_given(*args, **kwargs):
??????? """Dynamic validation decorator for scenario.
??????? :param args: the arguments of the decorator of the benchmark scenario
??????? ex. @my_decorator("arg1"), then args = ('arg1',)
??????? :param kwargs: the keyword arguments of the decorator of the scenario
??????? ex. @my_decorator(kwarg1="kwarg1"), then kwargs = {"kwarg1": "kwarg1"}
??????? """
??????? def wrap_validator(config, clients, task):
??????????? return (fn(config, clients, task, *args, **kwargs) or
??????????????????? ValidationResult())
??????? def wrap_scenario(scenario):
??????????? wrap_validator.permission = getattr(fn, "permission",
??????????????????????????????????????????????? consts.EndpointPermission.USER)
??????????? if not hasattr(scenario, "validators"):
??????????????? scenario.validators = []
??????????? scenario.validators.append(wrap_validator)
??????????? return scenario
??????? return wrap_scenario
??? return wrap_given

inspect庫的一些常見用法

inspect.getargspec(func) 獲取函數(shù)參數(shù)的名稱和默認值,返回一個四元組(args, varargs, keywords, defaults),其中:
args是參數(shù)名稱的列表;
varargs和keywords是*號和**號的變量名稱;
defaults是參數(shù)默認值的列表;

inspect.getcallargs(func[, *args][, **kwds]) 綁定函數(shù)參數(shù)。返回綁定后函數(shù)的入?yún)⒆值洹?

python中的私有屬性和函數(shù)

Python把以兩個或以上下劃線字符開頭且沒有以兩個或以上下劃線結(jié)尾的變量當作私有變量。私有變量會在代碼生成之前被轉(zhuǎn)換為長格式(變?yōu)楣校@個過程叫"Private name mangling",如類A里的__private標識符將被轉(zhuǎn)換為_A__private,但當類名全部以下劃線命名的時候,Python就不再執(zhí)行軋壓。而且,雖然叫私有變量,仍然有可能被訪問或修改(使用_classname__membername),所以, 總結(jié)如下:

無論是單下劃線還是雙下劃線開頭的成員,都是希望外部程序開發(fā)者不要直接使用這些成員變量和這些成員函數(shù),只是雙下劃線從語法上能夠更直接的避免錯誤的使用,但是如果按照_類名__成員名則依然可以訪問到。單下劃線的在動態(tài)調(diào)試時可能會方便一些,只要項目組的人都遵守下劃線開頭的成員不直接使用,那使用單下劃線或許會更好。


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