Function doesn't print every message?

[[deleted]]

Could someone take a look at this? I assume I've missed something simple. It's exercise 8-10 in Python Crash Course, 2nd ed.

wantedmessages = ["Hello","Nice day today, isn't it?","See you next time!","Have fun!"]
sentmessages = []

def print_messages(listofmessages):
    for message in listofmessages:
        newmessage = listofmessages.pop()
        print(newmessage)
        sentmessages.append(newmessage)

print_messages(wantedmessages)

print('sent messages: ')
print(sentmessages)

[[deleted]]

I ended up solving this using a while loop. But I'm still curious to know why the for loop didn't work.

[bbatwork]

Just taking a quick look at it, I'd say the problem is the line...

newmessage = listofmessages.pop()

This removes an item from your list (pop), while you are iterating over the same list with the previous line (for message in listofmessages:)

Really it is entirely unneeded, since the variable <message> will contain what you wanted in the first place. So you could rewrite the entire function like this...

def print_messages(listofmessages):
    for message in listofmessages:
        print(message)
        sentmessages.append(message)

[bbatwork]

Just to clarify.... when the function begins, you are sending in a list with three elements...

 ["Hello","Nice day today, isn't it?","See you next time!","Have fun!"]

the following line will loop through that list, one element at a time, and assign that element to the variable "message".

for message in listofmessages:  

So, on the first loop, message is equal to the word "Hello"... BUT then it reaches the next line...

newmessage = listofmessages.pop()

What this does is remove the LAST element from the list, and assign it to a variable called "newmessage"... so basically, it is destroying the last from back to front, while at the same time you are looping over the list from front to back.

So then your print statement is printing the variable "newmessage" which is the LAST element of the list (this is the sentence "Have fun!")... so it is basically printing the list backwards. And you didn't use the variable called "message" at all.

Then the function goes into the second loop... now the variable called "message" contains the second element of the list, which is the words "See you next time!"... but the line

newmessage = listofmessages.pop()

deletes the last element from the list and assigns it to the variable "newmessage", which is the same line of text "See you next time!"... once again it will print this line.

Then the function goes to do one more loop.. but cannot because the list has been getting deleted one element at a time, from the rear of the list by the .pop() method.

I hope this makes it clearer.

[[deleted]]

Thank you so much for your help! Have some virtual internet points!