负索引和切片 Python

Question

Long time reader first time poster, ever.

I am trying to understand all I can about indexing, slicing, negative indexing, etc. with lists.

If I have a list:

toeFriendly_terms=['feet', 'shoes', 'socks', 'sandals', 'boots', 'toe rings']

Ask 1: I would like to print() this list in reverse.

Q: Is it possible to use negative indexing to do this? Q: If so, how? Q: If not, what is the proper way to do this? Q: If you can do it but there is a better way how do you do it?

Ask 2: I looked around on here and found the.reverse() function but this opened up more questions.

names=['fanny', 'david', 'jimmy', 'hwang', 'esther']
#first three - fanny, david and jimmy
print('1. ', names[0:3])#stops right before 3 to give just what you need
#last three 
print('2. ', names[2:])#did not designate an end because I wanted all of it to come through
print('3. ', names[:-1]) #calls right up to before -1 
names2=names.reverse() #still affects the original list
print('4. ',names )

Q: Is there any way to preserve the original list so the reverse function doesn't affect whatever other work I've been doing with the list? (I am very new so I still do not fully understand if just duplicating the list is way easier or even more efficient..)

Q: What kind of real-world, 'on the job' applications does.reverse() have?

Thanks. That is all for now.

Answer 1

You are right in that calling some_list.reverse() mutates the original list, which you might expect or not (if not, keep reading).

You can use slicing to reverse the list like this: some_list[::-1] .

Note that there is always the reversed() method, which returns an iterator. If you want to get the reversed list all at once, you can just (surprise) turn it into a list: list(reversed(some_list)) .