What is a negative index?

Negative index in python :
  • Python list items can be accessed with positive or negative index. 
  • If list of size n then 
0 positive index // first index
1 positive index // second index
(n-1) // last index
-n // first index
-(n-1) // second
-1 // last index
  • List indexes of -x mean the xth item from the end of the list, so n[-1] means the last item in the list n.
  • Negative numbers mean that you count from the right instead of the left. So, list[-1] refers to the last element, list[-2] is the second-last, and so on.
  • Ex: 
    • If we have a list a = [1,2,3,4] then a[-1] will refer to 4 and a[-2] refer to 3.

Comments

Post a Comment

Popular posts from this blog

What is composite key?

Composite Key : A composite key is a combination of two or more columns in a table that can be used to uniquely identify each row in the table. When the columns are combined uniqueness is guaranteed but when it taken individually it does not guarantee uniqueness. Sometimes more than one attributes are needed to uniquely identify an entity. A primary key that is made by the combination of more than one attribute is known as a composite key. Ex : Create table abc ( c1 int , c2 varchar(20), c3 varchar(100) , PRIMARY KEY ( c1, c2 ) );
Keep reading

What are the different data types in Python?

Python Datatypes : Boolean Numbers Strings Lists Tuples Sets Dictionaries Boolean : Booleans are either true or false. Python has 2 constants named True and False which can be used to assign a boolean value directly. In certain places ( like if statements ), Python expects an expression to a boolean value, these places are called boolean contexts. Numbers : Python supports both int and floating point numbers. Tuples : A tuple is an immutable list, it means a tuple can't be changed in a way once it's created. A tuple is defined in the same way as a list, except that the whole set of an element is enclosed in the parenthesis instead of square brackets. Similarities with the list  : Tuples have a defined order i.e. Indices are 0 based, so the first element of a non-empty tuple is always a_tuple[ 0 ]. Negative indices count from the end of the tuple. Slicing works too, when we slice a list we get a new list. When we slice a tuple, we get a new t...
Keep reading

What is __repr__ function?

__repr__ function : The __repr__ function returns a string representation of a Python object that may be evaluated by the Python interpreter to instantiate another instance of the object. Called by the repr() built-in function and by string conversions (reverse quotes) to compute the "official" string representation of an object. repr() tries to convert everything into a string that can be used with eval() to re-generate the original object. repr() generates a computer friendly output. str() is used by print() function to generate a user-friendly output. str()'s output may or may not be used with eval(). >>> eval("'Hello'") 'Hello' >>> eval('Hello') Traceback (most recent call last):   File "<pyshell#8>", line 1, in <module>     eval(' Hello ')   File "<string>", line 1, in <module> NameError: name ' Hello ' is not defined
Keep reading