python 全局變量的import機(jī)制介紹
先把有問題的代碼曬一下:

IServer.py
from abc import ABCMeta, abstractmethod
print __name__
class IServer:
def __init__(self):
pass
@abstractmethod
def DoWithA(self):
pass
@abstractmethod
def DoWithB(self):
pass
IServer_A.py
import IServer
serverType ='1001'
print __name__
dir()
from CreatFactory import GLOBAL_class_dic
dir()
class IServer_A(IServer.IServer):
def __init__(self):
pass
def DoWithA(self):
print 'Server_A do with interface A'
def DoWithB(self):
print 'Server_A do with interface B'
global GLOBAL_class_dic
print 'the id of GLOBAL_class_dic in A is:',id(GLOBAL_class_dic)
GLOBAL_class_dic[serverType] = IServer_A
print 'GLOBAL_class_dic in a is:', GLOBAL_class_dic
IServer_B.py
import IServer
serverType ='1002'from CreatFactory import GLOBAL_class_dic
print __name__
class IServer_B(IServer.IServer):
def __init__(self):
pass
def DoWithA(self):
print 'Server_B do with interface A'
def DoWithB(self):
print 'Server_B do with interface B'
print 'the id of GLOBAL_class_dic in B is:',id(GLOBAL_class_dic)
GLOBAL_class_dic[serverType] = IServer_B
print 'GLOBAL_class_dic in b is:', GLOBAL_class_dic
CreatFactory.py
#coding:UTF-8
import os;
import sys;
import threading
from misc import *
global GLOBAL_class_dic
GLOBAL_class_dic ={1:1}
print 'GLOBAL_class_dic in define is:', GLOBAL_class_dic
print 'the id of GLOBAL_class_dic in define is:', id(GLOBAL_class_dic)
dir()
import IServer_A
import IServer_B
def CreateServer(serverType):
global GLOBAL_class_dic
print 'GLOBAL_class_dic in use is:', GLOBAL_class_dic
print 'the id of GLOBAL_class_dic in USE is:', id(GLOBAL_class_dic)
if GLOBAL_class_dic.has_key(serverType):
return GLOBAL_class_dic[serverType]
else:
return 'no'
if __name__ == '__main__':
pass
# 接收到報文后,根據(jù)報文的內(nèi)容,從db中獲取到serverType,假設(shè)獲取到的serverType=1001
print 'main'
print 'GLOBAL_class_dic in main A is:', GLOBAL_class_dic
serverType = '1002'
server = CreateServer(serverType)
print 'GLOBAL_class_dic in main B is:', GLOBAL_class_dic
print 'server :',server
server.DoWithA(server())
代碼內(nèi)已經(jīng)加了調(diào)試的部分信息, 運(yùn)行CreatFactory.py。調(diào)用DoWithA失敗,提示AttributeError: 'str' object has no attribute 'DoWithA'。運(yùn)行結(jié)果如下:
D:\Python27\python.exe "D:/DesignMode/Server --00/CreatFactory.py"
GLOBAL_class_dic in define is: {1: 1}
the id of GLOBAL_class_dic in define is: 36230176
['GLOBAL_class_dic', 'Misc', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'binascii', 'inspect', 'minidom', 'os', 'struct', 'sys', 'threading']
IServer
IServer_A
['IServer', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'serverType']
GLOBAL_class_dic in define is: {1: 1}
the id of GLOBAL_class_dic in define is: 36230032
['GLOBAL_class_dic', 'Misc', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'binascii', 'inspect', 'minidom', 'os', 'struct', 'sys', 'threading']
['IServer', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'serverType']
['GLOBAL_class_dic', 'IServer', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'serverType']
IServer_B
the id of GLOBAL_class_dic in B is: 36230032
GLOBAL_class_dic in b is: {1: 1, '1002': <class IServer_B.IServer_B at 0x022C2ED8>}
['GLOBAL_class_dic', 'IServer', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'serverType']
the id of GLOBAL_class_dic in A is: 36230032
GLOBAL_class_dic in a is: {1: 1, '1002': <class IServer_B.IServer_B at 0x022C2ED8>, '1001': <class IServer_A.IServer_A at 0x02273420>}
main
GLOBAL_class_dic in main A is: {1: 1}
GLOBAL_class_dic in use is: {1: 1}
the id of GLOBAL_class_dic in USE is: 36230176
GLOBAL_class_dic in main B is: {1: 1}
server : no
Traceback (most recent call last):
File "D:/DesignMode/Server --00/CreatFactory.py", line 38, in <module>
server.DoWithA(server())
AttributeError: 'str' object has no attribute 'DoWithA'
Process finished with exit code 1
從運(yùn)行的結(jié)果,可以看到:GLOBAL_class_dic 被定義了2次。有兩個不同的id,第一次定義分配了一塊內(nèi)存,第二次不明原因的又重新分配了一塊內(nèi)存,然后服務(wù)的自動注冊全部注冊在這塊內(nèi)存中,等到main函數(shù)使用的使用,又使用的是第一次申請的內(nèi)存,所以導(dǎo)致程序運(yùn)行失敗。那問題就來了,為什么會被重新又分配了一次?
之所以會被重新定義一次全局變量,是因為在執(zhí)行CreatFactory.py時,最開始定義了全局變量,此時該命名空間可使用的函數(shù)和變量打?。篬'GLOBAL_class_dic', 'Misc', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'binascii', 'inspect', 'minidom', 'os', 'struct', 'sys', 'threading',然后在import IServer_A,在IServer_A.py中,import IServer后,在from CreatFactory import GLOBAL_class_dic打印出可使用的函數(shù)和變量時,['IServer', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'serverType'],就沒有GLOBAL_class_dic,程序發(fā)現(xiàn)沒有,就又重新聲明了一遍。似乎問題原因已經(jīng)找到了。
python在導(dǎo)入的時候,有2種場景,一種就是在文件前普通的import語句,還有一種就是特殊的場景:__main__模塊是相對于Python的導(dǎo)入系統(tǒng)。在最開始運(yùn)行CreatFactory.py文件時,__name__打印的值是__main__,而再子類再次導(dǎo)入時,會在當(dāng)前命名空間查找是否已經(jīng)導(dǎo)入__name__=CreatFactory,發(fā)現(xiàn)這個模塊不存在,故此又導(dǎo)入了一遍,全局變量由此又被重新定義分配了內(nèi)存,后期全局變量在子類業(yè)務(wù)的使用就都使用該值,而在main函數(shù)里,使用的又是當(dāng)前的作用域內(nèi)的第一次定義的全局變量。
相關(guān)文章
Django用戶認(rèn)證系統(tǒng) Web請求中的認(rèn)證解析
這篇文章主要介紹了Django用戶認(rèn)證系統(tǒng) Web請求中的認(rèn)證解析,文中通過示例代碼介紹的非常詳細(xì),對大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價值,需要的朋友可以參考下2019-08-08
用Python中的wxPython實現(xiàn)最基本的瀏覽器功能
這篇文章主要介紹了用Python中的wxPython實現(xiàn)基本的瀏覽器功能,本文來自于IBM官方網(wǎng)站開發(fā)者文檔,需要的朋友可以參考下2015-04-04

