Transcript Lecture 2
CIT 590 Intro to Programming Lecture 2 Agenda • ‘import’ • Abstraction • Functions • Testing • The concept of scope One big giant python file …. • Python is full of modules • import math • from math import * • the same logic can be used for your own function • Example areaFuncs.py and usageOfFuncs.py Abstraction • A good program will have layers of abstraction • More often that not you only care about the input and output and do not really want or even need to know the internal workings • A well written function is like a blackbox converting input into meaningful output • math.sqrt() - how is implemented • Who cares! Modular programming • Software design technique that emphasizes separating the functionality of a program into independent, interchangeable modules • each module contains everything necessary to execute only one aspect of the desired functionality. • You’ll also hear this referred to as top-down design and stepwise refinement functions • In accordance with the concept of abstraction • Divide a program up into its ‘functional’ portions • Testing becomes much easier • Test each component really well – more on this later … • Think about a few integration tests • vowelCounter.py Information hiding • David Parnas first introduced the concept of information • • • • hiding around 1972. hiding "difficult design decisions or design decisions which are likely to change." Hiding information isolates clients from requiring intimate knowledge of the design to use a module, and from the effects of changing those decisions. Modular programming goes hand in hand with information hiding Whoever used your function is just relying on getting the right output for their input. So we can change the internal implementation safely Software reuse • Do not reinvent the wheel • The reuse of programming code is a common technique which attempts to save time and energy by reducing redundant work. • Software libaries/modules - good example of code reuse • In general if you are writing a program and you find yourself copy pasting code it is probably time to write a function. Good program design • Separate your program into the building blocks • Write a function for each of the building blocks • Simple methods of separation • Separate functions for the calculations • Separate function for the input • Separate function for the output The coke machine example • Cokemachine1 and cokemachine2.py • One of the examples modularizes code More modular programming • Using romanNumeral.py as an example • Is there a pattern that repeats itself when we are working with roman numerals • If you see a common pattern/repeated usage of the same code – convert that into a function! Scoping • local variables versus global variables • changing the value of a global variable within a function using the global keyword • Once you use the global keyword, you are changing the global variable as opposed to the variable that is just scoped to the function Summary • Understanding the importance of modular programming • Functions • Testing a function and code walkthroughs • Variable scope