todaytwo versions of python are availablepython and the newer python every programming language evolves as new ideas and technologies emergeand the developers of python have continually made the language more versatile and powerful most changes are incremental and hardly noticeablebut in some cases code written for python may not run properly on systems with python installed throughout this book 'll point out areas of significant difference between python and python so whichever version you useyou'll be able to follow the instructions if both versions are installed on your system or if you need to install pythonuse python if python is the only version on your system and you' rather jump into writing code instead of installing pythonyou can start with python but the sooner you upgrade to using python the betterso you'll be working with the most recent version running snippets of python code python comes with an interpreter that runs in terminal windowallowing you to try bits of python without having to save and run an entire program throughout this bookyou'll see snippets that look like thisu print("hello python interpreter!"hello python interpreterthe text in bold is what you'll type in and then execute by pressing enter most of the examples in the book are smallself-contained programs that you'll run from your editorbecause that' how you'll write most of your code but sometimes basic concepts will be shown in series of snippets run through python terminal session to demonstrate isolated concepts more efficiently any time you see the three angle brackets in code listing uyou're looking at the output of terminal session we'll try coding in the interpreter for your system in moment hello worlda long-held belief in the programming world has been that printing hello worldmessage to the screen as your first program in new language will bring you luck in pythonyou can write the hello world program in one lineprint("hello world!"such simple program serves very real purpose if it runs correctly on your systemany python program you write should work as well we'll look at writing this program on your particular system in just moment