{"id":101,"date":"2020-06-25T20:16:11","date_gmt":"2020-06-25T20:16:11","guid":{"rendered":"https:\/\/aaidm.buas.nl\/?page_id=101"},"modified":"2020-07-06T19:06:52","modified_gmt":"2020-07-06T19:06:52","slug":"pr1-week-1","status":"publish","type":"page","link":"https:\/\/aaidm.buas.nl\/?page_id=101","title":{"rendered":"PR1 – Preparation for Week 3 – Functions"},"content":{"rendered":"\n
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Author:<\/td>Carlos Santos<\/td><\/tr>
Learning Line:<\/td>Programming<\/td><\/tr>
Course:<\/td>PR1: Introduction to Programming<\/td><\/tr>
Week:<\/td>3<\/td><\/tr>
Competencies:<\/td>Students will be able to effectively define and use variables, programming flow control.<\/td><\/tr>
BoKS:<\/td>\u00ad 3bK2, The student understands the principles of data related software like Python, R, Scala and\/or Java and knows how to write (basic) scripts.<\/td><\/tr>
Learning Goals:<\/td>Variables and Data Types
In-code Comments<\/td><\/tr><\/tbody><\/table><\/figure>\n<\/div><\/div>\n\n\n\n

Functions<\/h3>\n\n\n\n

A function is a block of code which only runs when it is called. You can pass parameters, into a function, and it can return data as a result.<\/p>\n\n\n\n

You can see a function as a group of related instructions that performs a specific task. Functions help break our program into smaller chunks, it is the main way to support modular programming, and avoids repetition. In short makes the code reusable.<\/p>\n\n\n\n

It as very similar concept in math:<\/p>\n\n\n\n

f(x,y) = x^2+y<\/div>\n\n\n\n

can be written in python as:<\/p>\n\n\n\n

def f(x, y):\n  return x**2 + y\n\nf(2,3)\n7\nf(0,1)\n1<\/pre><\/div>\n\n\n\n
The premises are similar, f<\/em> is a function with two parameters x<\/em>, and y<\/em>. Parameters are special variables, normally required to calculate the result, of the function.<\/p>\n\n\n\n
Functions are not required to have parameters or return values.<\/p>\n\n\n\n
def printHello():\n  print("Hello function")\n\nprintHello()\nHello function<\/pre><\/div>\n\n\n\n
Parameter naming<\/h4>\n\n\n\n
The parameters names are important, since, you can use them to assure, you pass the correct information, and even reorder them is required.<\/p>\n\n\n\n
def show3(n1, n2, n3):\n  print("Show n1: " + str(n1))\n  print("Show n2: " + str(n2))\n  print("Show n3: " + str(n3))\n\nshow3(n3 = 3, n2 = 2, n1 = 1)\nShow n1: 1\nShow n2: 2  \nShow n3: 3<\/pre><\/div>\n\n\n\n
Important:<\/strong> The instructions set of a functions all have the same level, meaning they all have the same trailing number of spaces\/tabs. A function ends when the spacing returns to the previous level.<\/p>\n\n\n\n
Parameter Default values<\/p>\n\n\n\n
The parameters may have default values, it will assume the specified value if  not specified. This is where the parameters names are also very important.<\/p>\n\n\n\n
def g(a,b = 2, c= 1):\n  return a**b-c\n\ng(3)\n8\ng(3,2,3)\n6\ng(50,0)\n0\ng(2,c=3)\n1<\/pre><\/div>\n\n\n\n
Multiple return values<\/h4>\n\n\n\n
There is no limitations with regards to the number of return values, i.e., you can return more than one (not all programming languages allow this).<\/p>\n\n\n\n
def getNeighbours(x):\n  return x-1, x+1\n\ngetNeighbours(1)\n(0, 2)\nm, M = getNeighbours(3)\nprint(m)\n2\nprint(M)\n4<\/pre><\/div>\n\n\n\n
Scopes<\/h2>\n\n\n\n
Whenever you define a variable within a function, its scope lies ONLY within the function. It is accessible from the point at which it is defined until the end of the function. Which means its value cannot be changed or even accessed from outside the function. Let’s take a simple example:<\/p>\n\n\n\n
def functionScope():\n\tx = 10\n\tprint("Value inside function:"+str(x))\n\nx = 20\nfunctionScope()\nprint("Value outside function:"+str(x))<\/pre><\/div>\n\n\n\n
Note<\/strong> that in fact there are 2 variables declared, both are named x<\/em> (line 2 and 5). They are in different scopes, one inside of the function (named functionScope<\/em>), and the other in the base scope, known as global <\/strong>scope.<\/p>\n\n\n\n
Scopes are important concepts to grasp, since, it might bring you a lot of trouble if they are not handled correctly. In Python they are illustrated by the spacing at the beginning of the  instruction. This is called indentation<\/strong>.<\/p>\n\n\n\n
Note <\/strong>that variables that are declared in a specific scope are available in sub-scopes. <\/p>\n\n\n\n
a = 1\ndef functionThatUsesA(x):\n    return x + a\n  \nfunctionThatUsesA(3)\n4<\/pre><\/div>\n\n\n\n
This type of programming is to be avoided, not only it is confusing, but, also it may create weird artifacts, and becomes difficult to read. The following code is valid, although difficult to read even for experienced programmers. So it is better to avoid it.<\/p>\n\n\n\n
globalVar = 1\n\ndef functionScope1():\n    localVar1 = 2\n    localVar2 = 3\n    def functionScope2():\n        localVar1 = 4\n        localVar3 = 5\n        \n        return globalVar + localVar1 + localVar2 + localVar3\n    \n    return localVar1 + functionScope2()\n\nfunctionScope1()<\/pre><\/div>\n\n\n\n
Explanation: <\/p>\n\n\n\n