Python替代全局變量

Question

import random 

#----------------------------------------------# 
def main(): 
    create_list_and_find_max_and_min(10) 
    the_smart_way() 
#----------------------------------------------# 
def create_list_and_find_max_and_min(n): 
    global my_array 
    my_array = [] 
    n = input("How many numbers do you want in your array?:") 
    for i in range(n): 
     my_array.append(random.randint(1,n)) 
    print "My array is:", my_array 
    #----------------------------------------------# 
    min = my_array[0] 
    for number in my_array: 
    if min > number: 
     min = number 
    print "The minimum value in the array is:", min 
    #----------------------------------------------# 
    max = my_array[0] 
    for number in my_array: 
     if max < number: 
     max = number 
    print "The maximum value in the array is:", max 
#----------------------------------------------# 
def the_smart_way(): 
    # "This one uses the built-in Python functions for min/max..." 
    min_my_array = min(my_array) 
    max_my_array = max(my_array) 
    return min_my_array, max_my_array 
#----------------------------------------------# 
if __name__ == '__main__': 
    main() 

我對使用Python相當陌生。我一般都聽說在編程時使用全局變量是一種不好的做法。所以有什麼替代方案可以讓我在這裏做什麼。哪個是從另一個函數內部使用變量「my_array」？謝謝！

Answer 1

是的，有兩種選擇。

首先，您可以傳遞值而不是使用全局變量。例如，create_list_and_find_max_and_min可以在本地創建一個數組並返回它，那麼您可以在到the_smart_way傳遞：

import random 

#----------------------------------------------# 
def main(): 
    my_array = create_list_and_find_max_and_min(10) 
    print the_smart_way(my_array) 
#----------------------------------------------# 
def create_list_and_find_max_and_min(n): 
    my_array = [] 
    n = input("How many numbers do you want in your array?:") 
    for i in range(n): 
     my_array.append(random.randint(1,n)) 
    print "My array is:", my_array 
    #----------------------------------------------# 
    min = my_array[0] 
    for number in my_array: 
     if min > number: 
      min = number 
    print "The minimum value in the array is:", min 
    #----------------------------------------------# 
    max = my_array[0] 
    for number in my_array: 
     if max < number: 
      max = number 
    print "The maximum value in the array is:", max 
    return my_array 
#----------------------------------------------# 
def the_smart_way(my_array): 
    # "This one uses the built-in Python functions for min/max..." 
    min_my_array = min(my_array) 
    max_my_array = max(my_array) 
    return min_my_array, max_my_array 
#----------------------------------------------# 
if __name__ == '__main__': 
    main() 

其次，你可以創建一個封裝了對數據操作的數據和函數的類：

import random 

#----------------------------------------------# 
class MyArrayClass(object): 
    def create_list_and_find_max_and_min(self, n): 
     self.my_array = [] 
     n = input("How many numbers do you want in your array?:") 
     for i in range(n): 
      self.my_array.append(random.randint(1,n)) 
     print "My array is:", self.my_array 
     #----------------------------------------------# 
     min = self.my_array[0] 
     for number in self.my_array: 
      if min > number: 
       min = number 
     print "The minimum value in the array is:", min 
     #----------------------------------------------# 
     max = self.my_array[0] 
     for number in self.my_array: 
      if max < number: 
       max = number 
     print "The maximum value in the array is:", max 
    #----------------------------------------------# 
    def the_smart_way(self): 
     # "This one uses the built-in Python functions for min/max..." 
     min_my_array = min(self.my_array) 
     max_my_array = max(self.my_array) 
     return min_my_array, max_my_array 
#----------------------------------------------# 
def main(): 
    my_array = MyArrayClass() 
    my_array.create_list_and_find_max_and_min(10) 
    print my_array.the_smart_way() 
#----------------------------------------------# 
if __name__ == '__main__': 
    main() 

你或許應該明白原因全局變量是不好的做法。

想象一下，你想創建兩個數組。有了全局變量，第二個將取代第一個，這將永遠消失。

create_list_and_fix_max_and_min(10) 
create_list_and_fix_max_and_min(20) 
# No way to operate on the original array! 

有了一個局部變量，可以存儲他們兩個：

my_array_1 = create_list_and_fix_max_and_min(10) 
my_array_2 = create_list_and_fix_max_and_min(20) 
the_smart_way(my_array_1) 

使用對象提供相同的利益;兩者之間的差異最終歸結爲操作是否屬於數據含義的一部分，或數據是否獨立，操作是否通用。 （或者，你有時，不管你多一個功能勢利或OO勢利......的）

Answer 2

這裏是我會怎麼做：

import random 

#----------------------------------------------# 
def main(): 
    # note that input can be dangerous since it evaluates arbitrary code 
    n = int(raw_input("How many numbers do you want in your array?: ")) 
    my_list = [random.randint(1, n) for _ in range(n)] 
    find_max_and_min(my_list) 
    the_smart_way(my_list) 
#----------------------------------------------# 
def find_max_and_min(seq): 
    print "My array is:", seq 
    #----------------------------------------------# 
    min_num = seq[0] # Don't want to use same names as bultins here 
    for number in seq: 
     if number < min_num: 
      min_num = number 
    print "The minimum value in the array is:", min_num 
    #----------------------------------------------# 
    max_num = seq[0] 
    for number in seq: 
     if number > max_num: 
      max_num = number 
    print "The maximum value in the array is:", max_num 
#----------------------------------------------# 
def the_smart_way(seq): 
    # "This one uses the built-in Python functions for min/max..." 
    # No need for temp variables here 
    print min(seq), max(seq) 
#----------------------------------------------# 
if __name__ == '__main__': 
    main() 

Answer 3

功能做的事情對象，然後返回結果。您希望保持功能簡單並在功能之外執行所有邏輯和處理。這將消除對全局變量的需求，並使您的代碼更加容易閱讀。

話雖這麼說，這裏是我怎麼會攻擊你的問題：

import random 

def random_list(n=None): 
    n = n or int(raw_input('How many numbers do you want in your list? '))  

    return [random.randint(1, n) for i in range(n)] 

if __name__ == '__main__': 
    my_list = random_list(10) 
    minimum, maximum = min(my_list), max(my_list) 

    print 'My list is ', my_list 
    print 'The minimum value in the list is ', minimum 
    print 'The maximum value in the list is ', maximum