Application development with Python - Desktop application

About me ● My name: Nguyễn Đăng Bảo Long ● Current study: University of Engineering and Technology - VNU ● Main subject: Cloud Computing, Networking, Information Technology ● Email: baolong.a1yh@gmail.com

Get to know each other ● What do you do? ● How many of you have heard about programming? ● Have done some programming? Please share it

This course rule 1. Use the Google search as much as possible 2. Please ask me as much as possible (feel free to interrupt me if needed) 3. Repeat what I do as much as you can 4. You are allowed to use mobile phone, but use it wisely

Course objective After this course, you will be able to: ● Write your own applications ● Create a simple game from scratch ● Go on studying deeper in Python

Desktop app vs. Mobile app There were about 30 million lines of code in the Mac version of Microsoft Office (the whole suite) in 2006.

Let’s see how many kind of desktop app do you know You will have 2 minutes to write down all kind of desktop app you know. Let’s see who get the most number.

Phase 1: Idea ● An idea is given by a customer or a leader of a team ● There will be a draft where the app’s UI is sketched, the app’s functions is noted

Phase 2: Analysis & Design ● After all the requirements have been clarified, the devs are gonna choose which technology will be used. ● Then the dev team will focus on designing the: ○ UI ○ Components in the App (Login part, Paying part,...) ○ Back-end server, system ○ ...

Phase 3: Develop & Test ● At this phase, the dev team is actually do the coding, building the app part by part. ● Each part can be accomplished by a small team. ● There are some peoples, called “testers”, coming in to find any error in the app. ● The dev team then try to fix those errors, or “debug”

Phase 4: Deploy ● Bring up the app to the marketplace, where the user can use it ● At this stage, app will need to be advertised by the marketing team, in order to make it popular

Phase 5: Maintenance & Update ● After releasing, app shouldn’t be neglected. ● The team should continuously update it, improve it, keep making new functions.

What are we going to do in this course? ● We involve in the developing part ● Assume that all the ideas, requirements is exists, we just jump right in building it.

Technology (programming language) we use?

There are about 700 programming languages - Wikipedia

Why are we using it? ● Easy to learn ● Convenient to use ● Short to write code ● But: ○ Be careful with its syntax, 1 whitespace character can makes the difference

Python’s utility ● Small-to-big desktop apps ● AI, Machine Learning ● Web apps ● Mobile apps ● Data Analysis, tools,...

PART 1: PYTHON BASICS (Also coding basics)

In this part: 1. Install the prerequisites 2. Basic structure of a program 3. The output ○ To screen/file 4. The input ○ Variable ○ Data type ○ Operator 5. Execute part of a program ○ Logic ○ Loop ○ List ○ Function and Module

About Python ● Python is an interpreter ○ It’s a program which converts each of your line code, one by one, to a language which the computers can understand and execute it

Python version There are 2 version: ● Python 2 ● Python 3 (currently 3.8.1) We will use Python 3, since it’s the latest update

Python download and install (Windows) ● Go to the page https://www.python.org/downloads/windows/ and download the latest version of Python 3 ● Install it ● Set the environment variable for python (it already done by default) ● Check with cmd by typing python

Python download and install (Linux/Ubuntu) ● Open the Terminal ● Run the following command: ○ sudo apt install python3 ○ sudo apt install python3-pip ● Check with command python3

Python download and install (Mac OSX) ● Python 2 is installed on Mac by default, but we recommend using Python 3 ● Go to the page https://www.python.org/downloads/ and download the latest version of Python 3 ● Install it ● Set the environment variable for python (it already done by default) ● Check with terminal by typing python3

Python IDE Pycharm Visual Studio Code Text Editor

Python exploring Just put “python” before everything you want to search about Python

Alright, now you are ready to go!

Program “anatomy” Every app (or program) has 3 components: INPUT EXECUTE OUTPUT

Example Let’s have a simple example, at the coffee shop ● There are many choices on the menu for which the customer can orders. ● Each time, the customers will select 1 or more options for them and their friends. ● The program is to takes the orders, calculates the price, and prints out the bill.

Example analysis Input Execute Output Data about coffee: The menu, the price for each type of drink. Customer data: Which drinks do the customers order. Maps each drink to its price. Sums up all the prices. Displays on the screen for the customers. Prints out the bill.

So, how are we going to implement all of the above?

Let’s start with the easiest part first INPUT EXECUTE OUTPUT

The “print” Command ● Display something on your screen Type these lines in your IDE print(“Hello World”) print(“”” You can prints out every thing here It will output with the exact format “””)

How about writing to a file? You can use the “with open” statement, like this: with open(“aFile.txt”, “w”) as file: file.write(“Some random words in here”)

Oops, be careful with this indent with open(“aFile.txt”, “w”) as file: file.write(“Some random words in here”) This indent must be exactly 4 whitespace characters.

Let’s do a quick exercise Your job is to draw a mighty sword with any characters in a .doc file

Okay, let’s move to the second part INPUT EXECUTE OUTPUT

Same as output, there are 2 ways doing this

Input from keyboard You can prompt user with the input command, like below: input(“Prompting: “) input(“>>> “)

But, where do the inputs go? ● Do they just disappear??? ○ Yes and No ● We need to store them somewhere for future use, and that “somewhere” is called variables.

Variables Variables are like a closet. You can store any thing you want inside it, and take them out at any time you want

How to use it? The syntax to define a variable is variable_name = <something you want to store> For example: name = input(“Input your name here: “) print(name)

Other ways using variables ● With number: (You can do the calculating with these variables) age = 16 sum = 2 + 3 ( = 5 ) product = 5 * 6 ( = 30) quotient = 21 / 4 ( = 5.25) ● With boolean value: is_a_girl = True is_from_Japan = False

Be careful using it !!! ● It just works one way ○ This is good: number = 5 ○ This is bad: 5 = number ○ This is also bad: number1 = number2 = 5 ● Be careful naming the variables: ○ You can use lowercase, uppercase, number, underscore: downUp, UpDown, down_up, up1_down2 ○ Don’t put number at the beginning: 1_variable ○ Don’t use special character: not_this!, or_this?,... ○ Don’t use word that is used in Python syntax: if, else, for,...

Compare 2 variables bigger_number = 10 smaller_number = 7 compare = bigger_number > smaller_number (True) compare = bigger_number < smaller_number (False)

Compare 2 variables ● What if we want to know if 2 variables has the same value? ● We use 2 operator: == and != ○ compare = bigger_number == smaller_number ( ? ) ○ compare = bigger_number != smaller_number ( ? )

Variable data type ● What will happen if we compare 2 variable that has different data type? (E.g: a number and a character string) ○ number = 10 ○ word = “5” ○ compare = number > word ○ print(compare) ( ? ) ● We should convert them to the same data type and then do some operation on them ○ number2 = int(word) ○ compare = number > number2 ○ print(compare)

Data Type Conversion ● Four data type you should remember for now: int, float, str, bool ● Python syntax to switch between them: converted_value = <convert_data_type>(initial_value) ● Example: a_number = 3 a_string = str(a_number) print(a_string) ● Python syntax to check the variable type: type(variable)

An exercise to remember what we have learn so far ● A program that ask for the user’s name and Year of Birth ● Prints out a greeting with information like the following: Tips: There is something missing in the “print” command, Google search for it!

Okay, that’s all you need to know about input and output

Let’s dive into this part INPUT EXECUTE OUTPUT

Go back to the earlier example: The coffee shop How did the computer work after it has received the order? ● Remember the order ● For each drink in the customer’s order: ○ Look for it in the data (menu) ○ Add the associate price to the total cost in the bill ● Show the total price to the customer and the cashier

We divide that process into smaller pieces Input Assign the order to variables Get the name of the drink Get the name of the drink in the menu If 2 names are the same Add the price to the total cost Show the cost For each variable For each drink in the menu True How to solve this piece of problem

How to solve this piece of problem ● Remember how to compare 2 variables? ● How to direct the program in each case? Same and not same? If 2 names are the same

If … else.... Python syntax: if <conditional expression>: #Do something if the expression is true else: #Do something if the expression is false Also, this is call a comment Comment line start with the # character Computers will ignore every comment line In Condition Command block 1 Command block 2 Out False True

Example Write a program that ask for the user’s age, then tell them that they are: ● Young: if age < 20 ● Old: if age > 20 Next level: we use something call elif ● Baby: if age < 5 ● Young: if 5 < age < 18 ● Grow up: if 18 < age < 60 ● Old: if age > 60

Back to our previous example Espresso $5 Macchiato $7 Latte $8 Cappuccino $10 1 latte please!

Practice makes perfect... Create a program that: ● Require user’s input for weight and height ● Calculate the body mass index (BMI) ● Prints out the result to the screen (and may be some advice :p)

Another problem ● How to print out 1000 lines, each line has a word “Hello” in it? ● How about 1000*1000 lines? print(“Hello”) print(“Hello”) print(“Hello”) print(“Hello”) print(“Hello”) print(“Hello”) print(“Hello”) print(“Hello”) print(“Hello”) . . . . . . . . . . print(“Hello”) print(“”” Hello Hello Hello Hello Hello Hello Hello Hello . . . . . . . . . . Hello”””)

While ● To solve that problem, we use loop syntax ● In Python, we have 2 syntax for this: while command ○ while <conditional expression>: # Do some loop command here In Condition Command block Out False True

For… in... ● To solve that problem, we use loop syntax ● In Python, we have 2 syntax for this: for command ○ for i in range(0, <number of iterations>): # Do some loop command here ● range(start, stop, step) ● Why do we need to start from 0? In i < num Command block Out False True

Example A program that prints out a table that: ● Compare between 2 types of temperature measurement units: Celsius and Fahrenheit ● Start from 0 degree C to 100 degree C ● Each line is 10 degrees difference ● Use the following formula

Loop benefits ● Repeatedly does the same job, so you don’t have to write the same code for many lines ● Makes the source code of your program more readable

Keep practicing Build a program that: ● User inputs 1 number n (1<n<1000) ● If n is out of the above range, prints out the error ● Else, prints out the sum of all the number from 1 to n ● Please don’t use this formula, use loop statements instead

Comeback to our previous example Input Assign the order to variables Get the name of the drink Get the name of the drink in the menu If 2 names are the same Add the price to the total cost Show the cost For each variable For each drink in the menu True

How to store a huge number of value wisely? ● How about this piece of problem? ● What if the customer order 10 or 20 different drinks? ○ Store them in 20 variables is not a good idea ○ Naming each variable will become nightmare if the number of them increase ● Is there any another way to store this big number of value? Assign the order to variables

List Use to store values in an effective, organized way John 25 john@example.com Name Age Email John 25 john@example.com John’s information 22/2/1995 DOB 22/2/1995

How to use List ● Define a List: john_info = [“John”, 25, “22/2/1995”, “john@example.com”] ● How to use an element in the list: Try this: print(john_info[2])

How index works in a List? john_info = [“John”, 25, “22/2/1995”, “john@example.com”] 0 1 2 3

Actually, the “for” loop and “list” make the perfect match ● You can use for statement to get the values out of a list ● For each value in the list, we do something with it john_info = [“John”, 25, “22/2/1995”, “john@example.com”] for info in john_info: print(info)

Let’s check back the previous example ● Seems like we have everything we need to do all of this ● Let me show you how to implement all of this at one Input Assign the order to variables Get the name of the drink Get the name of the drink in the menu If 2 names are the same Add the price to the total cost Show the cost For each variable For each drink in the menu True

The last skill: Function and module ● Why do we need this? ○ Functions are like the blueprint of codes ○ You can reuse it as many time as you want without retyping the code ○ Make the program’s code more readable ● Syntax: def function_name(input_to_function): # Do something here ● Modules are like the collection of functions, you can share with others developer or keep it for later use

Prepare for next week ● Using pip3 to download and install pyqt5 tools

The work you can do at home ● At the end of each session, you will be given 1 problem which you can do at home. ● The result of your work will be assessed based on a variety of criteria. ● Each criteria passed, you will score some points. ● Candidates who get highest scores will have some gifts. Join this Google classroom: hydfs5h

Books you can read at home ● Learn Python The Hard Way - Zed Shaw (recommended!) ● Python rất là cơ bản - Võ Duy Tuấn ● Core Python Applications Programming - Wesley J Chun

Application development with Python - Desktop application

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