Programming Object Definition
Python offers a range of compound datatypes often referred to as sequences. List is one of the most frequently used and very versatile datatype used in Python.How to create a list?In Python programming, a list is created by placing all the items (elements) inside a square bracket , separated by commas.It can have any number of items and they may be of different types (integer, float, string etc.). # empty listmylist = # list of integersmylist = 1, 2, 3# list with mixed datatypesmylist = 1, 'Hello', 3.4Also, a list can even have another list as an item. This is called nested list.# nested listmylist = 'mouse', 8, 4, 6, 'a'How to access elements from a list?There are various ways in which we can access the elements of a list. List IndexWe can use the index operator to access an item in a list. Index starts from 0.
So, a list having 5 elements will have index from 0 to 4.Trying to access an element other that this will raise an IndexError. The index must be an integer. We can't use float or other types, this will result into TypeError.Nested list are accessed using nested indexing. Mylist = 'p','r','o','b','e'# Output: pprint(mylist0)# Output: oprint(mylist2)# Output: eprint(mylist4)# Error! Only integer can be used for indexing# mylist4.0# Nested Listnlist = 'Happy', 2,0,1,5# Nested indexing# Output: aprint(nlist01)# Output: 5print(nlist13)Negative indexingPython allows negative indexing for its sequences.
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The index of -1 refers to the last item, -2 to the second last item and so on. Mylist = 'p','r','o','b','e'# Output: eprint(mylist-1)# Output: pprint(mylist-5)How to slice lists in Python?We can access a range of items in a list by using the slicing operator (colon). Mylist = 'p','r','o','g','r','a','m','i','z'# elements 3rd to 5thprint(mylist2:5)# elements beginning to 4thprint(mylist:-5)# elements 6th to endprint(mylist5:)# elements beginning to endprint(mylist:). Slicing can be best visualized by considering the index to be between the elements as shown below. So if we want to access a range, we need two indices that will slice that portion from the list.How to change or add elements to a list?List are mutable, meaning, their elements can be changed unlike or.We can use assignment operator (=) to change an item or a range of items. # mistake valuesodd = 2, 4, 6, 8# change the 1st itemodd0 = 1# Output: 1, 4, 6, 8print(odd)# change 2nd to 4th itemsodd1:4 = 3, 5, 7# Output: 1, 3, 5, 7print(odd)We can add one item to a list using append method or add several items using extend method.
Odd = 1, 3, 5odd.append(7)# Output: 1, 3, 5, 7print(odd)odd.extend(9, 11, 13)# Output: 1, 3, 5, 7, 9, 11, 13print(odd)We can also use + operator to combine two lists. This is also called concatenation.The. operator repeats a list for the given number of times. Odd = 1, 3, 5# Output: 1, 3, 5, 9, 7, 5print(odd + 9, 7, 5)#Output: 're', 're', 're'print('re'. 3)Furthermore, we can insert one item at a desired location by using the method insert or insert multiple items by squeezing it into an empty slice of a list. Odd = 1, 9odd.insert(1,3)# Output: 1, 3, 9print(odd)odd2:2 = 5, 7# Output: 1, 3, 5, 7, 9print(odd)How to delete or remove elements from a list?We can delete one or more items from a list using the keyword del.
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It can even delete the list entirely. Mylist = 'p','r','o','b','l','e','m'# delete one itemdel mylist2# Output: 'p', 'r', 'b', 'l', 'e', 'm'print(mylist)# delete multiple itemsdel mylist1:5# Output: 'p', 'm'print(mylist)# delete entire listdel mylist# Error: List not definedprint(mylist)We can use remove method to remove the given item or pop method to remove an item at the given index.The pop method removes and returns the last item if index is not provided. This helps us implement lists as stacks (first in, last out data structure).We can also use the clear method to empty a list. Mylist = 'p','r','o','b','l','e','m'mylist.remove('p')# Output: 'r', 'o', 'b', 'l', 'e', 'm'print(mylist)# Output: 'o'print(mylist.pop(1))# Output: 'r', 'b', 'l', 'e', 'm'print(mylist)# Output: 'm'print(mylist.pop)# Output: 'r', 'b', 'l', 'e'print(mylist)mylist.clear# Output: print(mylist)Finally, we can also delete items in a list by assigning an empty list to a slice of elements. mylist = 'p','r','o','b','l','e','m' mylist2:3 = mylist'p', 'r', 'b', 'l', 'e', 'm' mylist2:5 = mylist'p', 'r', 'm'Python List MethodsMethods that are available with list object in Python programming are tabulated below.They are accessed as list.method.
If I wanted the command to output only certain applications, like Adobe, Visual Studio, and SQL Server, what would be the proper syntax? Preferably, I would like it to output just the 'parent' applications. For example, running the command above as is, returns a number of entries (amongst others) containing 'SQL', as some of them are 'sub-components' of the actual SQL server installation. I am just wanting the names and versions of the over arching parent applications, aforementioned.
Any comments and/or guidance would be appreciated.