Lecture 15: Collections in Python: Lists смотреть онлайн

Collections in Python: Lists
Collections in Python, are containers that are used to store collections of data, collection types are built-in in Python.
There are four collection data types in the Python programming language:
List is a collection which is ordered, indexed and elements in that list are changeable. Allows duplicate members in the list.
Tuple is a collection which is ordered, indexed and unchangeable elements in that collection. Allows duplicate members in the tuple.
Set is a collection which is unordered, unindexed and unchangeable elements. No duplicate members allowed in sets.
Dictionary is a collection which is unordered, changeable and indexed. No duplicate members.
When choosing a collection type, it is useful to understand the properties of that type and choose correct type for a particular data set.

Lists are just like the arrays declared in other languages. But the most powerful thing is that list need not be always homogenous like array.
A single list can contain strings, integers, as well as other types of objects.
A list is a collection which is ordered, indexed.
Lists are mutable, i.e., they can be altered once declared.
In Python lists are written with square brackets.
Example:
L = [“amol”,21,99.99 ]
print(L)
Lists can also be used for implementing stacks and queues data structures.
We can access the list items by referring to the index number:
L = ["amol", 21,99.99 ]
print(L[0]) # 0 index means first element in the list
Negative indexing means beginning from the end, -1 refers to the last item, -2 refers to the second last item and so on.
We can specify a range of indexes by specifying where to start and where to end the range.
When specifying a range, the return value will be a new list with the specified items.
print(L[3:5]) # List will be printed from stating index 3 which is included to index 5, which is excluded
By leaving out the start value, the range will start at the first item.
Example:
List = [“amol”,”suraj”,”kedar”,”samir”,”vijay”]
print(List[:3]) # returns items from start to kedar string
By leaving out the end value, the range will go on to the end of the list.
List = [“amol”,”suraj”,”kedar”,”samir”,”vijay”]
print(List[2:]) # returns items from second element to last element
Specify negative indexes if you want to start the search from the end of the list.
List = [“amol”,”suraj”,”kedar”,”samir”,”vijay”]
print(List[-3:-1]) # returns items from kedar to samir