一、单模块的全局变量

1、在函数外部定义x = 6
2、在函数内部再次定义global x

x = 6
def func():
    global x #定义外部的x
    x = 1

func()
print (x)
#输出1

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如果没有在函数内部global修饰，那么会在函数内部定义一个同名局部变量并隐藏掉同名全局变量。

二、多线程、跨模块的全局变量

为全局变量定义一个“全局变量管理模块”，下面主要创建了4个文件
多线程操作全局缓冲区时，最好增加同步锁Lock()

# main.py
import threading
import os
import global_maneger
from thread1 import modifycount
from thread2 import printcount


if __name__ == "__main__":
    print('主进程pid=%d'%os.getpid())
    global_maneger.set_global_buffer('rx_buffer', [0])
    global_maneger.set_global_value('count', 10)
    #创建线程，此线程修改全局变量
    t1=threading.Thread(target=modifycount)
    #创建线程，此线程打印全局变量
    t2=threading.Thread(target=printcount)
    t1.start()
    t2.start()
    t1.join()
    t2.join()
    print("主线程结束", global_maneger.get_global_buffer('rx_buffer'))


# global_maneger.py
import threading
_global_value_dict = {}
_global_buffer_dict = {}
buffer_lock = threading.Lock()
def set_global_value(key, value):
    """ 定义一个全局变量 """
    global _global_value_dict
    _global_value_dict[key] = value


def get_global_value(key, defValue=None):
    """ 获得一个全局变量,不存在则返回默认值 """
    global _global_value_dict
    try:
        return _global_value_dict[key]
    except KeyError:
        return defValue


def set_global_buffer(key, array):
    global _global_buffer_dict
    buffer_lock.acquire()
    _global_buffer_dict[key] = array
    buffer_lock.release()


def get_global_buffer(key):
    global _global_buffer_dict
    buffer_lock.acquire()
    result = _global_buffer_dict[key]
    buffer_lock.release()
    return result



# thread2.py
import threading
import time
import global_maneger

def printcount():
    #获取当前线程对象
    t=threading.current_thread()
    for index in range(global_maneger.get_global_value('count')):
        print('%s 打印buffer\n'%t.name, global_maneger.get_global_buffer('rx_buffer'))
        time.sleep(0.1)

# thread1.py
import threading
import time
import global_maneger

def modifycount():
    #获取当前线程对象
    t = threading.current_thread()
    for index in range(global_maneger.get_global_value('count')):
        print('%s 修改buffer\n'%t.name)
        array = global_maneger.get_global_buffer('rx_buffer')
        array.append(index)
        global_maneger.set_global_buffer('rx_buffer', array)
        time.sleep(0.1)

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main的运行结果：

主进程pid=8168
Thread-1 修改buffer

Thread-2 打印buffer
 [0, 0]
Thread-1 修改buffer
Thread-2 打印buffer

 [0, 0, 1]
Thread-1 修改buffer
Thread-2 打印buffer

 [0, 0, 1, 2]
Thread-1 修改buffer
Thread-2 打印buffer

 [0, 0, 1, 2, 3]
Thread-1 修改buffer
Thread-2 打印buffer

 [0, 0, 1, 2, 3, 4]
Thread-1 修改buffer
Thread-2 打印buffer

 [0, 0, 1, 2, 3, 4, 5]
Thread-2 打印buffer
Thread-1 修改buffer
 
[0, 0, 1, 2, 3, 4, 5]
Thread-1 修改buffer
Thread-2 打印buffer

 [0, 0, 1, 2, 3, 4, 5, 6, 7]
Thread-2 打印buffer
Thread-1 修改buffer
 
[0, 0, 1, 2, 3, 4, 5, 6, 7]
Thread-1 修改buffer
Thread-2 打印buffer

 [0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
主线程结束 [0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Process finished with exit code 0

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