100 Days of DevOps — Day 88-Lists in Python

Lists in Python

  • The list is a value that contains multiple values(mutable sequence)
>>> x = [1,2,’abc’,2.5]>>> x[1, 2, 'abc', 2.5]
  • We can access the item in the list with an integer index that start with 0(not 1)
>>> x[0]1
  • We can use the negative index to refer to the last item in the list
>>> x[-1]2.5
  • To get multiple items from the list use slice
>>> x[0:2][1, 2]#Basically grab every value of the list>>> x[0:][1, 2, 'abc', 2.5]
  • All the function that works with strings works in the same way with list eg:len()
>>> len(x)4
  • To delete the value from the list use del
>>> del x[0]>>> x[2, ‘abc’, 2.5]
  • We can convert a value into a list by passing it to the list() function
>>> list(‘hello’)[‘h’, ‘e’, ‘l’, ‘l’, ‘o’]
  • To find out the value in list use in operator
>>> ‘h’ in ‘hello’True#Opposite of that is not in operator>>> 'h' not in 'hello'False
  • Use of for loop with a list, so as you can see for loop iterate over the values in a list
>>> for i in x:… print(i)2abc2.5
  • range() function returns a list-like value which we can pass to the list() function if we need an actual value
>>> list(range(0,4))[0, 1, 2, 3]
>>> items = [“a”,”b”,”c”,”d”]
>>> for i in range(len(items)):
... print("Value at "+ str(i) + " is equal to: " + items[i])...Value at 0 is equal to: aValue at 1 is equal to: bValue at 2 is equal to: cValue at 3 is equal to: d
>>> a,b,c = 1,2,3>>> a1>>> b2>>> c3
  • index() list method returns the index of an item in the list
>>> test = [“a”,”b”,”c”,”d”]>>> test.index(“a”)0# Index method will raise the exception if it doesn't find the value>>> test.index("e")Traceback (most recent call last):File "<stdin>", line 1, in <module>ValueError: 'e' is not in list# Now in case of duplicate list it only return the index of first value>>> test = ["a","b","c","d","a","b"]>>> test.index("b")1
  • append() list method adds value to the end of a list
>>> test.append(“z”)>>> test[‘a’, ‘b’, ‘c’, ‘d’, ‘a’, ‘b’, ‘z’]
  • insert() list method adds value anywhere inside a list
>>> test.insert(0,”hola”)>>> test[‘hola’, ‘a’, ‘b’, ‘c’, ‘d’, ‘a’, ‘b’, ‘z’]
  • remove() list method removes an item, specified by the value from a list
>>> test.remove(“a”)>>> test  #Only first incident of that value is removed[‘hola’, ‘b’, ‘c’, ‘d’, ‘a’, ‘b’, ‘z’]
  • reverse(): A list can be reversed by calling its reverse() method
>>> a = [2,5,1,3,6,4]>>> a.reverse()>>> a[4, 6, 3, 1, 5, 2]
  • sort() list method sorts the items in a list
>>> test1 = [8,3,9,4,6,3]>>> test1.sort()>>> test1[3, 3, 4, 6, 8, 9]
>>> test2 = [1,2,3,”a”,”b”]>>> test2 = [1,3,2,6,5,”a”,”b”]>>> test2.sort()Traceback (most recent call last):File “<stdin>”, line 1, in <module>TypeError: ‘<’ not supported between instances of ‘str’ and ‘int’
>>> test3 = [‘a’,’b’,’A’,’B’]>>> test3.sort()>>> test3[‘A’, ‘B’, ‘a’, ‘b’]
>>> test3.sort(key=str.lower)>>> test3[‘A’, ‘a’, ‘B’, ‘b’]# The important use case of key, where we use len as a key(here sorting happens based on the length)
>>> b
['hello', 'how', 'are', 'u', 'Mr', 'Prashant']>>> b.sort(key=len)>>> b['u', 'Mr', 'how', 'are', 'hello', 'Prashant']
  • Sorted(): built-in function sorts any iterable series and returns a list
>>> x = [5,2,3,1]>>> sorted(x)[1, 2, 3, 5]>>> x[5, 2, 3, 1]
  • count(): Count returns the number of matching elements
>>> a = [1,2,3,4,1,23,5,6]>>> a.count(1)2
>>> test = [1,2,3,4]>>> test1 = test>>> test1[1, 2, 3, 4]>>> test1[0] = 9>>> test1[9, 2, 3, 4]>>> test[9, 2, 3, 4]
test1 = test
>>> a = “abc”>>> b = a>>> b = “efg”# Change in b will not impact a
>>> b
‘efg’>>> a‘abc
  • id(): returns a unique identifier for an object
>>> x = 100>>> id(x)4340331440>>> x = 50>>> id(x)4340329840
>>> x = [1,2,3]>>> import copy>>> y = copy.deepcopy(x)>>> y[1, 2, 3]>>> y[0] = 4>>> y[4, 2, 3]>>> x[1, 2, 3]
>>> a = [4,5,6]>>> b = a[:]>>> b[4, 5, 6]>>> id(a)4325208200>>> id(b)4325208328>>> b[0] = 10>>> b[10, 5, 6]>>> a[4, 5, 6]




AWS Community Builder, Ex-Redhat, Author, Blogger, YouTuber, RHCA, RHCDS, RHCE, Docker Certified,4XAWS, CCNA, MCP, Certified Jenkins, Terraform Certified, 1XGCP

Love podcasts or audiobooks? Learn on the go with our new app.

Recommended from Medium

Linux Network Namespace Usage

Adding Life to Your Social Media Icons

Application Layer Protection for Istio Service Mesh

Understanding Git

Best AdBlocker for Uninterrupted Web Browsing and Protecting your Data — AdGuard

Adapter Design Pattern

GraphQL in Production with Hasura Cloud

Emulate the Firebase Realtime Database API with Golang, Postgres, and Websockets

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store
Prashant Lakhera

Prashant Lakhera

AWS Community Builder, Ex-Redhat, Author, Blogger, YouTuber, RHCA, RHCDS, RHCE, Docker Certified,4XAWS, CCNA, MCP, Certified Jenkins, Terraform Certified, 1XGCP

More from Medium

Python Security “logging.config” code execution

Docker: Zero to Hero with Linux Example

Bash Scripting for Beginners (Part 1 — Introduction and Variables)

PyOps — Scapy Introduction