Basic Python Programming: Part 01 and Part 02

Topic 00 Basic Python Programming – Part 01 Fariz Darari, Ph.D. Machine Learning Specialization for Geoscientists In collaboration with FMIPA UI v04

print("Python" + " is " + "cool!") "Python is easy to use, powerful, and versatile, making it a great choice for beginners and experts alike." – Pluralsight Platform 2 public class Main { public static void main(String[] args) { System.out.println("Hello world!"); } } print("Hello world!") Hello world in Java vs. Python

print("Python" + " is " + "cool!") 3 Big names using Python "Python is easy to use, powerful, and versatile, making it a great choice for beginners and experts alike." – Pluralsight Platform

print("Python" + " is " + "cool!") "Python is easy to use, powerful, and versatile, making it a great choice for beginners and experts alike." – Pluralsight Platform 4opencv.org

print("Python" + " is " + "cool!") "Python is easy to use, powerful, and versatile, making it a great choice for beginners and experts alike." – Pluralsight Platform 5pygame.org

print("Python" + " is " + "cool!") "Python is easy to use, powerful, and versatile, making it a great choice for beginners and experts alike." – Pluralsight Platform 6http://flask.palletsprojects.com/

print("Python" + " is " + "cool!") "Python is easy to use, powerful, and versatile, making it a great choice for beginners and experts alike." – Pluralsight Platform 7 matplotlib.org

print("Python" + " is " + "cool!") "Python is easy to use, powerful, and versatile, making it a great choice for beginners and experts alike." – Pluralsight Platform 8 https://github.com/amueller/word_cloud

print("Python" + " is " + "cool!") 9 Top programming languages 2019 by IEEE Spectrum

Let's now explore the Python universe!

How to install Python the Anaconda way 1. Download Anaconda (which includes Python and relevant libraries): https://www.anaconda.com/distribution/ 2. Run the installer and follow the instructions 3. Run the Spyder editor or Jupyter Notebook and create your first Python program "helloworld.py" 11 Python Setup

A more enhanced hello program 12 name = "Dunia" # can be replaced with another value print("Halo, " + name + "!")

A more and more enhanced hello program 13 print("Halo, " + input() + "!")

Create a program to calculate the area of a circle! 14

Create a program to calculate the area of a circle! 15 Step 1: Minta nilai jari-jari. Step 2: Hitung sesuai rumus luas lingkaran. Step 3: Cetak hasil luasnya.

Create a program to calculate the area of a circle! 16 # Step 1: Minta nilai jari-jari. jari2 = input("Jari-jari: ") jari2_int = int(jari2) # Step 2: Hitung sesuai rumus luas lingkaran. luas = 3.14 * (jari2_int ** 2) # Step 3: Cetak hasil luasnya. print(luas)

Similar program, now with import math 17 import math # Step 1: Minta nilai jari-jari. jari2 = input("Jari-jari: ") jari2_int = int(jari2) # Step 2: Hitung sesuai rumus luas lingkaran. luas = math.pi * (math.pow(jari2_int,2)) # Step 3: Cetak hasil luasnya. print(luas)

Quiz: Create a program to calculate square areas! 18

Quiz: Create a program to calculate square areas! 19 # Step 1: Minta nilai panjang sisi. # Step 2: Hitung sesuai rumus luas persegi. # Step 3: Cetak hasil luasnya. print(luas)

Quiz: Create a program to calculate square areas! 20 # Step 1: Minta nilai panjang sisi. sisi = input("Sisi: ") sisi_int = int(sisi) # Step 2: Hitung sesuai rumus luas persegi. luas = sisi_int * sisi_int # Step 3: Cetak hasil luasnya. print(luas)

input("some string") 21 It's a function to print "some string" and simultaneously ask user for some input. The function returns a string (sequence of characters). PS: If not wanting to print anything, just type: input()

Assignment 22 The = symbol is not for equality, it is for assignment: "Nilai di sebelah kanan diasosiasikan dengan variabel di sebelah kiri" Contohnya, x = 1. PS: x = 1 berbeda dengan x == 1. More on this later.

Assignment 23 Example: my_var = 2 + 3 * 5 • evaluate expression (2+3*5): 17 • change the value of my_var to 17 Example (suppose my_int has value 2): my_int = my_int + 3 • evaluate expression my_int on RHS to: 2 • evaluate expression 2 + 3: 5 • change the value of my_int to 5

Type conversion 24 The int() function as we saw before is for converting string to int. Why? Because we want to do some math operations! But what if the string value is not converted to int? Well, try this out: "1" + "1" Other type conversions: float() , str()

print(var, "some string") 25 Well, it prints. It may take several elements separated by commas: - If the element is a string, print as is. - If variable, print the value of the variable. Note that after printing, we move to a new line.

Save program as module 26 Program yang disimpan disebut dengan Python module, dan menggunakan file extension .py Jadi, module adalah sekumpulan instruksi Python. Module dapat dieksekusi, atau diimpor dalam module lain (ingat module math).

Memberi komentar pada program 27 Komentar atau comment adalah cara untuk semakin memperjelas alur program kita. Komentar tidak dapat dijadikan excuse untuk kode program yang berupa spaghetti code (berantakan). Komentar pada Python dimulai dengan # (hash), atau diapit dengan petik tiga """ untuk komentar multibaris.

• Variables store and give names to data values • Data values can be of various types: • int : -5, 0, 1000000 • float : -2.0, 3.14159 • bool : True, False • str : "Hello world!", "K3WL" • list : [1, 2, 3, 4], ["Hello", "world!"], [1, 2, "Hello"], [ ] • And many more! • In Python, variables do not have types! This is called: Dynamic typing. • A type defines two things: • The internal structure of the type • Operations you can perform on type (for example, capitalize() is an operation over type string) 28 Variables and Data Types

Name convention • Dimulai dengan huruf atau underscore _ • Ac_123 is OK, but 123_AB is not. • Dapat mengandung letters, digits, and underscores • this_is_an_identifier_123 • Panjang bebas • Upper and lower case letters are different (case sensitive) • Length_Of_Rope is not the same as length_of_rope 29

Namespace Namespace adalah tabel yang mengandung pemetaan antara variable dan nilai datanya. 30

31 Python Variables and Data Types in Real Life

Operators 32 • Integer • addition and subtraction: +, - • multiplication: * • division: / • integer division: // • remainder: % • Floating point • add, subtract, multiply, divide: +, -, *, /

Logical operators: and, or, not 36

Logical operators: and, or, not 37

39 Conditionals: Simple Form if condition: if-code else: else-code

40 Conditionals: Generic Form if boolean-expression-1: code-block-1 elif boolean-expression-2: code-block-2 (as many elif's as you want) else: code-block-last

41 Conditionals: Usia SIM age = 20 if age < 17: print("Belum bisa punya SIM!") else: print("OK, sudah bisa punya SIM.")

42 Conditionals: Usia SIM dengan Input age = int(input("Usia: ")) if age < 17: print("Belum bisa punya SIM!") else: print("OK, sudah bisa punya SIM.")

43 Conditionals: Grading grade = int(input("Numeric grade: ")) if grade >= 80: print("A") elif grade >= 65: print("B") elif grade >= 55: print("C") else: print("E")

• Useful for repeating code! • Two variants: 44 Loops while boolean-expression: code-block for element in collection: code-block

45 While Loops x = 5 while x > 0: print(x) x -= 1 print("While loop is over now!") while boolean-expression: code-block

46 While Loops while boolean-expression: code-block

47 While Loops while boolean-expression: code-block while input("Which is the best subject? ") != "Computer Science": print("Try again!") print("Of course it is!")

So far, we have seen (briefly) two kinds of collections: string and list For loops can be used to visit each collection's element: 48 For Loops for element in collection: code-block for chr in "string": print(chr) for elem in [1,3,5]: print(elem)

Range function 49 • range merepresentasikan urutan angka (integer) • range memiliki 3 arguments: – the beginning of the range. Assumed to be 0 if not provided. – the end of the range, but not inclusive (up to but not including the number). Required. – the step of the range. Assumed to be 1 if not provided. • if only one argument is provided, assumed to be the end value

Eksplorasi range 50 for i in range(10): print(i, end=" ") print() for i in range(1,7): print(i, end=" ") print() for i in range(0,30,5): print(i, end=" ") print() for i in range(5,-5,-1): print(i, end=" ")

Lirik lagu menggunakan range 51 syg = "sayang" for i in range(2): print("satu") print("aku", syg, "ibu") print() for i in range(2): print("dua") print("juga", syg, "ayah") print() for i in range(2): print("tiga") print(syg, "adik", "kakak") print() for i in range(1,4): print(i) print(syg, "semuanya")

• Functions encapsulate (= membungkus) code blocks • Why functions? Modularization and reuse! • You actually have seen examples of functions: • print() • input() • Generic form: 52 Functions def function-name(parameters): code-block return value

• Functions encapsulate (= membungkus) code blocks • Why functions? Modularization and reuse! • You actually have seen examples of functions: • print() • input() • Generic form: 53 Functions def function-name(parameters): code-block return value

54 Functions: Celcius to Fahrenheit def celsius_to_fahrenheit(celsius): fahrenheit = celsius * 1.8 + 32.0 return fahrenheit def function-name(parameters): code-block return value

55 Functions: Default and Named Parameters def hello(name_man="Bro", name_woman="Sis"): print("Hello, " + name_man + " & " + name_woman + "!") >>> hello() Hello, Bro & Sis! >>> hello(name_woman="Lady") Hello, Bro & Lady! >>> hello(name_woman="Mbakyu",name_man="Mas") Hello, Mas & Mbakyu!

• Code made by other people shall be reused! • Two ways of importing modules (= Python files): • Generic form: import module_name import math print(math.sqrt(4)) • Generic form: from module_name import function_name from math import sqrt print(sqrt(4)) 58 Imports

Make your own module 59 def lame_flirt_generator(name): print("A: Knock-knock!") print("B: Who's there?") print("A: Love.") print("B: Love who?") print("A: Love you, " + name + " <3") import mymodule mymodule.lame_flirt_generator("Fayriza") mymodule.py example.py

• String is a sequence of characters, like "Python is cool" • Each character has an index • Accessing a character: string[index] x = "Python is cool" print(x[10]) • Accessing a substring via slicing: string[start:finish] print(x[2:6]) 60 String P y t h o n i s c o o l 0 1 2 3 4 5 6 7 8 9 10 11 12 13

>>> x = "Python is cool" >>> "cool" in x # membership >>> len(x) # length of string x >>> x + "?" # concatenation >>> x.upper() # to upper case >>> x.replace("c", "k") # replace characters in a string 61 String Operations P y t h o n i s c o o l 0 1 2 3 4 5 6 7 8 9 10 11 12 13

>>> x = "Python is cool" >>> x.split(" ") 62 String Operations: Split P y t h o n i s c o o l 0 1 2 3 4 5 6 7 8 9 10 11 12 13 P y t h o n 0 1 2 3 4 5 i s 0 1 c o o l 0 1 2 3 x.split(" ")

>>> x = "Python is cool" >>> y = x.split(" ") >>> ",".join(y) 63 String Operations: Join P y t h o n , i s , c o o l 0 1 2 3 4 5 6 7 8 9 10 11 12 13 P y t h o n 0 1 2 3 4 5 i s 0 1 c o o l 0 1 2 3 ",".join(y)

Quiz: Transform the following todo-list "wake up,turn off alarm,sleep,repeat" into "wake up$turn off alarm$sleep$repeat" 64

Quiz: Transform the following todo-list "wake up,turn off alarm,sleep,repeat" into "wake up$turn off alarm$sleep$repeat" 65 todo_list = "wake up,turn off alarm,sleep,repeat" todo_list_split = todo_list.split(",") todo_list_new = "$".join(todo_list_split) print(todo_list_new)

Topic 00 Basic Python Programming – Part 02 Fariz Darari, Ph.D. Machine Learning Specialization for Geoscientists In collaboration with FMIPA UI v04

Recursion WIKIPEDIA A function where the solution to a problem depends on solutions to smaller instances of the same problem THINK PYTHON BOOK A function that calls itself

Factorial Mathematical definition: n! = n x (n – 1) x (n – 2) x . . . . . . x 2 x 1 Example: 5! = 5 x 4 x 3 x 2 x 1 = 120

Factorial Recursive definition: n! = n x (n – 1)! Example: 5! = 5 x 4!

Factorial Recursive definition: n! = n x (n – 1)! Example: 5! = 5 x 4! PS: Where 0! = 1 and 1! = 1

Factorial in Python def faktorial(num): # function header

Factorial in Python def faktorial(num): # function header # 0! or 1! return 1 if (num == 0) or (num == 1): return 1

Factorial in Python def faktorial(num): # function header # 0! or 1! return 1 if (num == 0) or (num == 1): return 1 # do recursion for num > 1 return num * faktorial(num-1)

Main components of recursion def faktorial(num): # BASE CASE if (num == 0) or (num == 1): return 1 # RECURSION CASE return num * faktorial(num-1) • Base case Stopping points for recursion • Recursion case Recursion points for smaller problems

• You've learned that a string is a sequence of characters. A list is more generic: a sequence of items! • List is usually enclosed by square brackets [ ] • As opposed to strings where the object is fixed (= immutable), we are free to modify lists (= mutable). 76 Lists x = [1, 2, 3, 4] x[0] = 4 x.append(5) print(x) # [4, 2, 3, 4, 5]

77 List Operations >>> x = [ "Python", "is", "cool" ] >>> x.sort() # sort elements in x >>> x = x[0:2] # slicing >>> len(x) # length of string x >>> x = x + ["!"] # concatenation >>> x[1] = "hot" # replace element at index 1 with "hot" >>> x.remove("Python") # remove the first occurrence of "Python" >>> x.pop() # remove the last element

It is basically a cool way of generating a list 78 List Comprehension [expression for-clause condition] Example: ["Aku tidak akan bolos lagi" for i in range(100)]

It is basically a cool way of generating a list 79 List Comprehension [expression for-clause condition] Example: ["Aku tidak akan bolos lagi" for i in range(100)] [i*2 for i in [0,1,2,3,4] if i%2 == 0]

It is basically a cool way of generating a list 80 List Comprehension [expression for-clause condition] Example: ["Aku tidak akan bolos lagi" for i in range(100)] [i*2 for i in [0,1,2,3,4] if i%2 == 0] [i.replace("ai", "uy") for i in ["Santai", "kyk", "di", "pantai"] if len(i) > 3]

• Like a list, but you cannot modify/mutate it • Tuple is usually (but not necessarily) enclosed by parentheses () • Everything that works with lists, works with tuples, except functions modifying the content • Example: 81 Tuples x = (0,1,2) y = 0,1,2 # same as x x[0] = 2 # this gives an error

• As opposed to lists, in sets duplicates are removed and there is no order of elements! • Set is of the form { e1, e2, e3, ... } • Operations include: intersection, union, difference. • Example: 83 Sets x = [0,1,2,0,0,1,2,2] # list y = {0,1,2,0,0,1,2,2} # set print(x) print(y) # observe difference list vs set print(y & {1,2,3}) # intersection print(y | {1,2,3}) # union print(y - {1,2,3}) # difference

84 Dictionaries • Dictionaries map from keys to values! • Content in dictionaries is not ordered. • Dictionary is of the form { k1:v1, k2:v2, k3:v3, ... } • Example: x = {"indonesia":"jakarta", "germany":"berlin","italy":"rome"} print(x["indonesia"]) # get value from key x["japan"] = "tokyo" # add a new key-value pair to dictionary print(x) # {'italy': 'rome', 'indonesia': 'jakarta', 'germany': 'berlin', 'japan': 'tokyo'}

Quiz: What is the output? Hint: https://www.python-course.eu/python3_dictionaries.php x = {"a":3, "b":4} y = {"b":5, "c":1} print(x) x.update(y) print(x) print(x.keys()) print(x.values()) 86

Lambda expression Lambda expressions - also known as anonymous functions - allow you to create and use a function in a single line. They are useful when you need a short function that you will only use once. >>> (lambda x: 3*x + 1)(3) 10 88

Quiz: What does this code do? items = [1, 2, 3, 4, 5] squared = [] for i in items: squared.append(i**2) 89

Map map(function_to_apply, list_of_inputs) 90 Map applies function_to_apply to all the items in list_of_inputs

Using lambda+map, the squared code can be shortened items = [1, 2, 3, 4, 5] squared = list(map(lambda x: x**2, items)) 91

Lambda expression Sort a list of names based on the last name. lst = ["Bob Wick", "John Doe", "Louise Bonn"] lst.sort(key=lambda name:name.split(" ")[-1]) print(lst) # ['Louise Bonn', 'John Doe', 'Bob Wick'] 92

• Working with data heavily involves reading and writing! • Data comes in two types: • Text: Human readable, encoded in ASCII/UTF-8, example: .txt, .csv • Binary: Machine readable, application-specific encoding, example: .mp3, .mp4, .jpg 94 Input/Output

python is cool 95 Input cool.txt x = open("cool.txt", "r") # read mode y = x.read() # read the whole content print(y) x.close()

python is cool 96 Input cool.txt x = open("cool.txt", "r") # read line by line, printing if not containing "py" for line in x: if not ("py" in line): print(line, end="") x.close()

97 Output # write mode x = open("carpe-diem.txt", "w") x.write("carpendiemn") x.close() # append mode x = open("carpe-diem.txt", "a") x.write("carpendiemn") x.close() Write mode overwrites files, while append mode does not overwrite files but instead appends at the end of the files' content

Input and Output in Real Life 98

99 Errors • Errors dapat muncul pada program: syntax errors, runtime errors, logic/semantic errors • Syntax errors: errors where the program does not follow the rules of Python. For example: we forgot a colon, we did not provide an end parenthesis • Runtime errors: errors during program execution. For example: dividing by 0, accessing a character past the end of a string, a while loop that never ends. • Semantic/logic errors: errors due to incorrect algorithms. For example: Program that translates English to Indonesian, even though the requirement was from English to Javanese.

Quiz: What type error is in this is_even function? 100 def is_even(n): if n % 2 == 0: return False else: return True

101 Error handling in Python Basic idea: • keep watch on a particular section of code • if we get an exception, raise/throw that exception (let the exception be known) • look for a catcher that can handle that kind of exception • if found, handle it, otherwise let Python handle it (which usually halts the program)

102 print(a) try: print(a) except NameError: print("Terjadi error!") VS Compare

Generic form 103 try: code block except a_particular_error: code block

Type conversion feat. exception handling 104 var_a = ["satu", 2, "3"] for x in var_a: try: b = int(x) print("Berhasil memproses", x) except ValueError: print("ValueError saat memproses", x)

File accessing feat exception handling 105 # opening a file with exception handling try: x = open("this-does-not-exist.py") x.close() except FileNotFoundError: print("Berkas tidak ditemukan!") # vs. # opening a file without exception handling x = open("this-does-not-exist.py") x.close()

• While in functions we encapsulate a set of instructions, in classes we encapsulate objects! • A class is a blueprint for objects, specifying: • Attributes for objects • Methods for objects • A class can use other classes as a base, thus inheriting the attributes and methods of the base class 107 Classes class class-name(base): attribute-code-block method-code-block

But why? • Bundle data attributes and methods into packages (= classes), hence more organized abstraction • Divide-and-conquer • Implement and test behavior of each class separately • Increased modularity reduces complexity • Classes make it easy to reuse code • Class inheritance, for example, allows extending the behavior of (base) class 108 Classes

109 Object-oriented programming: Classes as groups of similar objects

110 Object-oriented programming: Classes as groups of similar objects class Cat class Rabbit

class Person: is_mortal = True def __init__(self, first, last): self.firstname = first self.lastname = last def describe(self): return self.firstname + " " + self.lastname def smiles(self): return ":-)" 111 Classes: Person class class-name(base): attribute-code-block method-code-block # code continuation.. guido = Person("Guido","Van Rossum") print(guido.describe()) print(guido.smiles()) print(guido.is_mortal)

112 Classes: Person & Employee class class-name(base): attribute-code-block method-code-block # extending code for class Person class Employee(Person): def __init__(self, first, last, staffnum): Person.__init__(self, first, last) self.staffnum = staffnum def describe(self): return self.lastname + ", " + str(self.staffnum) jg = Employee("James", "Gosling", 5991) print(jg.describe()) print(jg.smiles()) print(jg.is_mortal)

113 Quiz: What is the output? class Student: def __init__(self, name): self.name = name self.attend = 0 def says_hi(self): print(self.name + ": Hi!") ali = Student("Ali") ali.says_hi() ali.attend += 1 print(ali.attend) bob = Student("Bob") bob.says_hi() print(bob.attend)

What's next: Learning from books 115 https://greenteapress.com/wp/think-python-2e/

What's next: Learning from community 116https://stackoverflow.com/questions/tagged/python

What's next: Learning from community 117https://www.hackerearth.com/practice/

What's next: Learning from academics 118https://www.coursera.org/courses?query=python

What's next: Learning from me :-) 119https://www.slideshare.net/fadirra/recursion-in-python

What's next: Learning from me :-) 120https://twitter.com/mrlogix/status/1204566990075002880

121 Food pack is ready, enjoy your journey!

Basic Python Programming: Part 01 and Part 02

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