Question

Why do we need to use "elif" instead of just another instance of "if" statement? I can understand "else" being necessary.

Answer 1

Basically, elif is a short hand for else if (different languages use a different keyword. I've seen elif, elsif and else if). The advantage of using a else if is that your indentation does not suffer.

Take for example a simple test:
if n == 1:
# do something
elif n == 2:
# Do something else
elif n == 3:
# Do a third thing
else
# Do a final thing

Without the elif this would have to become:
if n == 1:
# Do something
else
if n == 2:
# Do something else
else:
if n == 3:
# Do a third thing
else:
# Do a final thing

Imagine a larger series of if ... else if statements. It would be easy to make a mistake with indentation there, while the elif keeps things nice and readable.

Answer 2

If you have several possibilities, elif allows your condition to only have to be evaluated once and the result chosen from the various if/elif/else. A series of if statements require the condition to be evaluated every time, which can be expensive.

If this is Python, Python is unusual in that it doesn't have a switch statement ( you may want to check a site like http://www.cprogramming.com ). They use the if/elif/else instead, ostensibly to be easier to read. I'll bet that down in the interpreter, it's doing a switch statement.

Answer 3

Thank you for your replies. @slotema, I had suspected that but wasn't sure why not just repeat the "if" statement until an "else" is needed, I see we can repeat an elif instead.
@rsmith on a side note, you remind me how much I love The Cure ;)
Yes this is python, I should have mentioned that. Thanks again. Really enjoying the lectures (I was previously learning ruby the hard way ;))