Python|从给定列表中删除尾随的空元素

给定一个列表，任务是从列表的最后一个中删除尾随的None值。让我们讨论一些解决给定任务的方法。

例子：

Input: [1, 2, 3, 4, None, 76, None, None]
Output:  [1, 2, 3, 4, None, 76]

Input: [1, 2, None, None, None, None, None, 5]
Output:  [1, 2, None, None, None, None, None, 5]

方法#1：使用朴素的方法

# Python code to demonstrate
# to remove trailing None
# elements from lists
  
# initialising lists
ini_list = [1, 2, 3, 4, None, 76, None, None, None]
  
# printing initial dictionary
print ("initial dictionary", str(ini_list))
  
# code toremove trailing None values
# from lists
while not ini_list[-1]:
    ini_list.pop()
      
# printing result
print ("resultant list", str(ini_list))

输出：

initial dictionary [1, 2, 3, 4, None, 76, None, None, None]
resultant list [1, 2, 3, 4, None, 76]

方法 #2：使用itertools.dropwhile()

# Python code to demonstrate
# to remove trailing None
# elements from lists
  
from itertools import dropwhile
# initialising lists
ini_list = [1, 2, 3, 4, None, 76, None, None, None]
  
# printing initial dictionary
print ("initial dictionary", str(ini_list))
  
# code toremove trailing None values
# from lists
res = list(reversed(tuple(dropwhile(lambda x: x is None, 
                                    reversed(ini_list)))))
      
# printing result
print ("resultant list", str(res))

输出：

initial dictionary [1, 2, 3, 4, None, 76, None, None, None]
resultant list [1, 2, 3, 4, None, 76]

方法 #3：使用itertools.takewhile()

# Python code to demonstrate
# to remove trailing None
# elements from lists
  
from itertools import takewhile
  
# initialising lists
ini_list = [1, 2, 3, 4, None, 76, None, None, None]
  
# printing initial dictionary
print ("initial dictionary", str(ini_list))
  
# code toremove trailing None values
# from lists
res = ini_list[:-len(list(takewhile(lambda x: x == None,
                                  reversed(ini_list))))]
# printing result
print ("resultant list", str(res))

输出：

initial dictionary [1, 2, 3, 4, None, 76, None, None, None]
resultant list [1, 2, 3, 4, None, 76]

方法#4：使用枚举和列表推导

# Python code to demonstrate
# to remove trailing None
# elements from lists
  
  
# initialising lists
ini_list = [1, 2, 3, 4, None, 76, None, None, None]
  
# printing initial dictionary
print ("initial dictionary", str(ini_list))
  
# code toremove trailing None values
# from lists
res = [x for n, x in enumerate(ini_list)
       if any(y is not None for y in ini_list[n:])]
  
# printing result
print ("resultant list", str(res))

输出：

initial dictionary [1, 2, 3, 4, None, 76, None, None, None]
resultant list [1, 2, 3, 4, None, 76]