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

3
Big names using Python

4opencv.org

5pygame.org

6http://flask.palletsprojects.com/

7
matplotlib.org

8
https://github.com/amueller/word_cloud

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

15
Step 1: Minta nilai jari-jari.
Step 2: Hitung sesuai rumus luas lingkaran.
Step 3: Cetak hasil luasnya.

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))
print(luas)

Quiz: Create a program to calculate square areas!
18

19
# Step 1: Minta nilai panjang sisi.
# Step 2: Hitung sesuai rumus luas persegi.
print(luas)

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
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!")
code-block

46
While Loops
code-block

47
While Loops
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
code-block
return value

54
Functions: Celcius to Fahrenheit
def celsius_to_fahrenheit(celsius):
fahrenheit = celsius * 1.8 + 32.0
return fahrenheit
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!

56
>>> hello()
Hello, Bro & Sis!
Hello, Bro & Lady!

57
>>> hello()
Hello, Bro & Sis!
Hello, Bro & Lady!

• 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
0 1 2 3 4 5 6 7 8 9 10 11 12 13

>>> x.split(" ") 62
String Operations: Split
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(" ")

>>> 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
# 0! or 1! return 1
if (num == 0) or (num == 1):
return 1

Factorial in Python
# 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)]

79
List Comprehension
Example:
[i*2 for i in [0,1,2,3,4] if i%2 == 0]

80
List Comprehension
Example:
[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
method-code-block
# code continuation..
guido = Person("Guido","Van Rossum")
print(guido.describe())
print(guido.smiles())
print(guido.is_mortal)

112
Classes: Person & Employee
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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