Python Apps with PyQt5

️: This presentation will use live polls for feedback: http://etc.ch/g7KN
️: Q1-Q3
: I will pause for questions at a few locations, other questions are welcome in the middle opf the presentation depending on the size of the group.

Programming in General

Programming is the art of creating software for computers.
Programming can come in many forms, but the majority of professional programming is done with text languages that appear like a combination of English and mathematics.
- The program is a sequence of instructions that the computer follows.
- This is referred to as code.
Programs are generally composed of 6 major types of instructions:
1. Variable declarations and assignments
  - These define spaces for data to be stored and update those spaces with new data.
2. Arithmetic instructions
  - These compute new values using basic arithmetic as well as comaprisons and some other operations.
  - Typically these are combined with variable assignments to store the result of the computation.
3. Input and output instructions
  - These are instructions that provide output to the user or read input from the user.
  - These can include text, such as a basic program that takes in text answers and prints text results.
  - This can also include graphics and sounds as output and keyboard, mouse and joystick inputs, as is done in games.
4. Conditional instructions
  - These are instructions that make other instructions execute only if certain conditions are met.
5. Repetition instructions
  - These are instructions that make other instructions execute repeatedly.
  - The number of repetitions can be as low as zero or theoretically infinite.
6. Subroutines
  - These are instructions that are placed in a separate location so that they can be executed by other instructions.
  - This is done to break apart a large program into smaller peices.
  - This is also done to allow some instructions to be used in multiple places without having to copy those instructions multiple places.

Python Concepts

Python is a scripting language
- Another name for this is an interpreted language
- This means that typically the computer is analyzing each instruction that the programmer has written only when it is going to be executed.
- The advantage of this is that you do not have to wait for a separate compilation step before you run your program.
- The disadvantage is that if you make an obvious mistake in the code, you will not get an error until that line of code is reached in your program.
Python is a dynamically-typed language
- This means that it does not check that a value has the correct type until it is used in some way.
- This is also called Duck Typing
  
  "If it looks like a duck and quacks like a duck, it’s a duck."
Python is particular about how you indent and use whitespace
- Whitespace is the technical term for any spaces, tabs or newlines in a text file.
- To group together instructions, you must indent all instructions at the same level.
- Python considers indentation with tabs to be different from indentation with spaces, even if they look the same.

: Any questions?

Programming Methods

Python has two main methods for programming, interactive and by loading instructions from a file.
In interactive mode, Python responds to instructions as you type them.
- To start, type python at the command line to start Python in interactive mode.
  - You may need to type python3 to get the correct version of Python.
- To quit, type quit() on a new line (or press CTRL-D).

: Demo

The alternative to this is to type instructions into a text file and then run those instructions.
- To run a script, you must be in the same directory as your program on the command line.
- Type python yourScript.py at the command line to start Python and run your program.
  - Again, you may need to use python3 to get the correct version of Python.

: Demo

In addition, to help those that do not want to install python or who are unable to install it (because they are using a Chromebook or do not have permission to install programs), there are several online websites that allow you to write Python code and execute it on the website. One example of this is repl.it.

: Demo

️: Q4-Q6
: Any questions?

Installation Instructions

You only need to install Python if you want to work on your local machine instead of in an online platform like repl.it.
Install Python 3:
- You may have python installed already. Try running python --version at a command prompt to see if it works and that you have at least version 3.5.
- Installation instructions can be found here.
Install PyQt5:
- Installation instructions can be found here. They make use of pip, which is a program that should come with Python.

: Any questions?
: 5-10 minute break to get Python set up or sign up for repl.it

Python Basics

Variables

Variables hold data.
A variable can hold a number, text a list of values or combinations of the above.
A variable is identified by a name.
- apples
- count
- x
Since spaces have meaning, variable names with multiple words can't have spaces.
Instead, tpyically the underscore _ (shift - on most keyboards) is used to separate words, e.g.:
- apple_count
- my_favourite_variable
While typing longer variable names can be tiresome, it is generally considered better to use more descriptive names to help you remember and others understand what the intention of the variable is.
- You can use g, but it doesn't mean anything.
- A name like count is better, but still not very descriptive.
- The best names are really obvious: apple_count.
Placing a value in a variable is done by putting the variable name followed by and equals sign = followed by the value.
```
count = 5
```
You can change a variable's value many times.
```
count = 5
count = 4
count = 6
```
Only the final value of each variable is saved, the rest are lost.
When you place text in a variable, it is called a string value.
This is done using either single quotes ' or double quotes " to start and stop the string.
Whatever you use to start the string must also be used to end the string (both single quotes or both double quotes).

Arithmetic

You can use +, -, * and / for addition, subtraction, multiplication and division.
The result of arithmetic can be saved in a variable just like any other value.
```
count = 5
price = 1.20
total = count * price
```
You can use parentheses ( and ) (but not square brackets) to give order to arithmetic just like in your math course.
There are two unusual arithmetic operators: // is integer division and % is modulo.
- They act like divide and remainder from elementary school.
- // will round down to the next integer so that 8 // 3 will equal 2 since 5 goes into 3 only 2 whole times.
- % will give the remainder after integer division so that 8 % 3 will equal 2 since there is 2 left after taking out 3 from 5.

: Demo

Input and Output

Reading input at the console can be done using input("Prompt text: ").
- Whatever you put instead of "Prompt text: " will be show to the user to hlpe them know what you are asking.
- The prompt text is optional.
The result of this can be saved to a variable for processing.
```
favourite_fruit = input("Enter your favourite fruit: ")
```
This always gives you a string value.
To convert it to a number, you must use int() or float() to convert it to a number.
- int() should be used when you want an integer (a whole number). It will fail if it is given a decimal point.
- float() should be used when you want a number that might have a decimal point in it.
```
count = int(input("Enter the count (whole number): "))
price = float(input("Enter the price: "))
```
Output is done using print().
Whatever you want printed should be put between the parentheses.
You can print a string, a number or a variable's value.
```
print(5)
value = 7.6
print(value)
print("Wheee!")
```
Fancier formatting can be done using a formatted string literal
- These are regular strings that have an f character before the opening quote.
- Variables can be put into the string by surrounding them with curly brackets { and }.
- These can be used outside of printing too!
```
value = 2.99
item = 'pig statue'
print(f'The value is {value} and the item is {item}')
```

: Demo

️: Q7
: Any questions?
️: Work on a basic program to read in some numbers and compute a value.

More Python

Conditions

To only do something some of the time, you can use the if instruction.
- After if you place a condition.
- After the condition is a colon :
- The code that might be executed is in the next few lines, indented.
- If the condition is true, the code indented under the if instruction will be executed.
```
count = int(input("Enter the count (whole number): "))

if count % 2 == 1:
    print("That is an odd count!")
```

If you want to have two options, you can use elif and else in a chain of possibilities.

count = int(input("Enter the count (whole number): "))

if count % 2 == 1:
    print("That is an odd count!")
else:
    print("")

: Demo

Loops

To something over and over again, you can use the while instruction.
- After while you place a condition.
- After the condition is a colon :
- The code that should be executed over and over again is in the next few lines, indented.
- While the condition is true, the code indented under the while will be executed.
- Note that this may run zero times or 1 or many.
```
count = int(input("Enter the count (whole number): "))

while count % 2 == 1:
  print("The count must be an even number!")

  count = int(input("Enter the count (whole number): "))
```
- Note: After the loop we know that count must be even.

: Demo

To something over and over again, you can use the for instruction with range().
- The format is for i in range(count).
- The value count indicates how often the loop will run. It could be a variable or a literal value.
- The variable i (which can use any name you'd like) will have a value of 0 the first time the loop runs, 1 the next, etc.
```
count = int(input("Enter the count (whole number): "))

for range(count):
    print(f"I've run {i} times so far")
```
- Note: I had to use double quotes " for the string since there was a single quote ' inside it.

: Demo

Functions

Functions allow you to separate instructions into reusable parts so you can break apart your program or reduce how often you have to repeat yourself.
- Defining a function uses the def keyword.
- Then you put the function name. Function names have the same rules as variable names.
- Then you put an open parenthesis ( and a comma-separated list of parameters and finally a closing parenthesis ) and a colon :.
  - The parameters are inputs to the function and must be given when you use the function.
- That line is called the function header.
- The instructions for the function are indented and below the function header.
```
def my_function(parameter):
    print(f'This is inside my function; I got {parameter}')
```
Functions can be used by calling them.
- This is done by using the function name followed by an open parenthesis ( and a comma-separated list of parameters and finally a closing parenthesis )
  - The parameters in this case are when you want the parameters to be inside the function this time.
```
my_function(6)
my_function("pig")
```
Functions can return a value by using the return instruction as the last line in the function.
- This returned value can be used by the calling code
```
def gimme():
    return 42
    
value = gimme()
```
- At this point, value will have a value of 42 because it was returned by the function.

: Demo

: Any questions?
: 5-10 minute break

PyQt5

Skeleton code

We'll start with the skeleton code available on this repl.it.

: Demo

Components

Here is a list of some of the components available in PyQt5:

QLabel: A text label useful for labeling buttons or other things on your application.
QLineEdit: A text box for entering a text value.
QPushButton: A simple button that the user can click.
QCheckbox: A checkbox that can be checked or not.
QComboBox: A dropdown list box that holds a set of possible options.
QRadioButton: A set of circular buttons where you can only select one at a time.
QDial: Rotateable dial for inputing a number. You can control the minimum and maximum values.

There are other controls listed in the documentation.

Layout

To lay out the controls in your application, you will likely use on of these layouts:

QVBoxLayout: Linear vertical layout with each item above or below the next item.
QGridLayout: A 2D grid that can hold items.

If possible, I'd recommend starting with QVBoxLayout and only move to QGridLayout if you need something more complex.

️: Q8

Python Apps with PyQt5

Programming in General

Python Concepts

Programming Methods

Installation Instructions

Python Basics

Variables

Arithmetic

Input and Output

More Python

Conditions

Loops

Functions

PyQt5

Skeleton code

Components

Layout

Other Topics

Resources