python引用變量的順序： 當前作用域局部變量->外層作用域變量->當前模塊中的全局變量->python內置變量
一 global
global關鍵字用來在函數或其他局部作用域中使用全局變量。但是如果不修改全局變量也可以不使用global關鍵字。
gcount = 0
def global_test():
print (gcount)
def global_counter():
global gcount
gcount +=1
return gcount
def global_counter_test():
print(global_counter())
print(global_counter())
print(global_counter())
def global_test():
print (gcount)
def global_counter():
global gcount
gcount +=1
return gcount
def global_counter_test():
print(global_counter())
print(global_counter())
print(global_counter())
二 nonlocal
nonlocal關鍵字用來在函數或其他作用域中使用外層(非全局)變量。
def make_counter():
count = 0
def counter():
nonlocal count
count += 1
return count
return counter
def make_counter_test():
mc = make_counter()
print(mc())
print(mc())
print(mc())
count = 0
def counter():
nonlocal count
count += 1
return count
return counter
def make_counter_test():
mc = make_counter()
print(mc())
print(mc())
print(mc())
也可以使用generator來實現類似的counter。如下：
def counter_generator():
count = 0
while True:
count += 1
yield count
def counter_generator_test():
# below is for python 3.x and works well
citer = counter_generator(). __iter__()
i = 0
while(i < 3) :
print(citer. __next__())
i+=1
def counter_generator_test2():
# below code don't work
# because next() function still suspends and cannot exit
# it seems the iterator is generated every time.
j = 0
for iter in counter_generator():
while(j < 3) :
print(iter)
j+=1
count = 0
while True:
count += 1
yield count
def counter_generator_test():
# below is for python 3.x and works well
citer = counter_generator(). __iter__()
i = 0
while(i < 3) :
print(citer. __next__())
i+=1
def counter_generator_test2():
# below code don't work
# because next() function still suspends and cannot exit
# it seems the iterator is generated every time.
j = 0
for iter in counter_generator():
while(j < 3) :
print(iter)
j+=1
完！