L=[1,2,3] 
print(L[L[2]])

What will be the output? I am a beginner to python and I am confused by this specific thing in List. I am not understanding what this means.

CodePudding user response：

I 'm going to explain with this list (because you will get IndexError with current list):

L = [1, 2, 3, 4, 5]
print(L[L[2]])

First, Python sees the print() function, in order to call this function, Python has to know it's arguments. So it goes further to evaluate the argument L[L[2]].

L is a list, we can pass an index to the bracket to get the item at that index. So we need to know the index. We go further and calculate the expression inside the first []. It's L[2].

Now we can easily evaluate the expression L[2]. The result is 3.

Take that result and put it instead of L[2]. our full expression is print(L[3]) at the moment.

I think you get the idea now...

From inside to the outside:

step1 -- >  print(L[L[2]])
step2 -- >  print(L[3])
step3 -- >  print(4)

CodePudding user response：

Here what you are doing is, you are getting the value at 2 which should be 3, because python starts from 0 and goes up. So after that the interior braces should be done, and then you find the index at 3 which is too big. Because the indexes only go up to 2, and if I say I had three numbers, and you ask me what the fourth number is, that wouldn't make sense right? So that is the same thing. This would result in an error.

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
IndexError: list index out of range

This means that you are trying to get a value that does not exist. I hope this makes it clear.

CodePudding user response：

L[L[2]] becomes L[3], since L[2] is equal to 3. Then, since there are three elements in L, and indexing starts at 0 in Python, this would result in an IndexError.