在代码完成检查每个选项后，是否可以使我的else语句出现？

Question

I have a while loop that goes over a two-dimensional list, to see if it can find a similar submission for it to be removed.

    i=0

while i <= len(my_list):
    if my_list[i] == userinput:
        del my_list[i]
        print("Entry Removed!")
    else:
        print("This publication does not exist")
    i+=1

What I wanted was for the code to print the message "This publication does not exist" if no matches were found. However, what happens right now is that everytime it compares an item, the code prints the sentence.

I understand why this happens but I have no idea how to fix it. What is the best way of addressing this issue?

EDIT: Changed list name from "list" to "my_list". My bad, I didn't actually call it that in the code, I just changed the name when uploading the question for ease of understanding.

Answer 1

You'll need to a boolean:

i = 0
found = False
while i <= len(list):
    if list[i] == userinput:
        del list[i]
        print("Entry Removed!")
        found = True
    i += 1

if not found:
    print("This publication does not exist")

Some unrelated suggestions:

• It is better to not use the name list for a variable

• Don't remove items from a list while iterating that same list. You can iterate the list in reverse:

   i = len(li) - 1 found = False while i >= 0: if li[i] == userinput: del li[i] print("Entry Removed!") found = True i -= 1 if not found: print("This publication does not exist") 

Answer 2

Python's while loop has an else clause that executes if the loop completes without breaking out of it:

But let's go another way with this to avoid changing a list we are looping over:

list_ = [
    ["a", "b", "c"], 
    ["d", "f", "g"], 
    ["d", "f", "g"], 
    ["h", "i", "j"]
]

userinput = ["z", "z", "z"]
new_list = [x for x in list_ if x != userinput]

if list_ == new_list:
     print("This publication does not exist")

# This publication does not exist

Don't overwrite the list keyword. I changed it to list_ but you can change it to something more meaningful for your application.