1 — Programming Basics

In the beginning was the Tao. The Tao gave birth to Space and Time. Therefore Space and Time are the Yin and Yang of programming. — Tao of Programming

Binary Numbers

In decimal system, a number is expressed as a sequence of digits $0$ to $9$ .

For example, Two thousand twenty one ⇔ 2021

In binary number system the set of digits, is called binary digits or bits: $\{0, 1\}$ .

A binary number is expressed as a sequence of bits.

For example, $183$ in binary is $10110111$ .

Converting from decimal to binary

Enter decimal number:

	Quotient	Remainder
123 / 2	61	1
61 / 2	30	1
30 / 2	15	0
15 / 2	7	1
7 / 2	3	1
3 / 2	1	1
1 / 2	0	1

Collecting remainders from bottom to top, 123 in binary is 1111011

Converting from binary to decimal

Enter binary number:

1 × 2³

0 × 2²

1 × 2¹

1 × 2⁰

1 × 8

0 × 4

1 × 2

1 × 1

Groups of bits

A group of $8$ bits is called a byte e.g. $11010111$

$1$ kilobyte (kB) = $1000$ bytes
$1$ megabyte (MB) = $10^6$ (million) bytes
$1$ gigabyte (GB) = $10^9$ (billion) bytes
$1$ terabyte (TB) = $10^{12}$ bytes (1000 billion)

What is programming?

Programming is the process of creating a set of instructions — a program — to tell a computer how to perform a task.

Programs take input data, perform some computation — numerical or symbolic (text) — and produce output data.

Computers can perform only basic binary operations (such as add or multiply two numbers)

How do we communicate complex instructions to computers? — Use a programming language!

Levels of programming languages

Low-level languages	High-level languages
Closer to machine, difficult for humans	Closer to humans, easier for humans to work with

Less portable, provide less abstraction over hardware	More portable, more abstraction over hardware
Examples: Assembly Language	Examples: Java, Python

How do computers understand high-level languages?

High-level languages are translated into machine code (for CPU).

Programming languages come in two main flavors — compiled languages or interpreted languages.

Compilers and interpreters are software tools responsible to translate source code into machine code.

Compiled languages (e.g. C/C++, Java)

High-level program (source code) ➞ Compiler ➞ Binary executable (e.g. .exe or .dmg)
Once compiled, the binary program can be executed without compiler.

Interpreted (e.g. Python, Ruby)

High-level program (source code) ➞ Executed directly by an Interpreter
The interpreter is required on the machine where the program is executed.

Data in binary

Computers can understand only binary numbers

How can we encode data in the real world into binary numbers?

Integers in binary

We already saw how to represent positive integers in binary e.g.

109 = 1101101_2

For signed integers (to differentiate negative and positive), an extra leftmost bit is used for sign only, e.g.

-109 = \colorbox{lightblue}{1}1101101_2

+109 = \colorbox{lightblue}{0}1101101_2

(For more info: https://en.wikipedia.org/wiki/Signed_number_representations)

Real numbers in binary

64-bit Floating point format is used to represent numbers with decimal point, e.g.

\colorbox{lightblue}{0}\colorbox{lightpink}{10000000000}\colorbox{lightgreen}{1001001000011111101101010100010001000010110100011000} = 3.141592653589793

(For more info: https://en.wikipedia.org/wiki/Double-precision_floating-point_format)

Floating point format has a finite precision, but digits of $\pi$ run forever:

3.1415926535897932384626433832795028841...

With only 64-bits, we can only have precision up to a fixed digits after decimal point: $3.141592653589793$

Text in binary

Letters and punctuations in human languages are encoded in binary using a Character Encoding such as ASCII or UTF-8 (Unicode).

(source: https://simple.wikipedia.org/wiki/ASCII)

Images, audio & video in binary

Binary data is stored in a file using a specific format.

Programs know what to do (play music, show image, etc) based on the format.

We already know some of these formats:

Images: jpeg, png
Audio: mp3, m4a, wma
Video: mp4, avi, wmv

Thonny Demo — Editor vs Shell

Python interpreter works in two modes:

An interactive Shell mode (with the prompt >>>)
- Line(s) of code is executed immediately as soon entered and output is visible immediately
Script mode
- Executes a Python file (.py) as a program.

Thonny allows us to use both modes in one graphical interface.

Comments

Comments are annotations we add to our program and are ignored by the Python interpreter.

In Python, we start a comment using #.

1# Author: Deven
2# My first program
3
4# This is a comment on its own line & it will be ignored
5print("Hello, world!")  # str
6print(123)  # int
7print(1.614)  # float

We use comments to:

Make the code easier to read and understand by explaining how it works.
Indicate authorship and license.
Disable some code (prevent it from executing) but still keeping it in the file.

In Thonny, we can use Edit menu -> Toggle comment to comment/uncomment the selected lines.

Objects and Data Types

All data in a Python program is represented by objects.

An object always has a type (or class) associated with it.

We can use type() function to know the type of an object.

>>> type(5)
<class 'int'>

>>> type(3.1415)
<class 'float'>

>>> type("Hello")
<class 'str'>

An object’s type determines the operations that the object supports:

1#  objects of int type can be added using +
2>>> 10 + 5
315
4
5# But an object of type str cannot be added to an int using +
6>>> "Hello" + 5
7Traceback (most recent call last):
8  File "<pyshell>", line 1, in <module>
9TypeError: can only concatenate str (not "int") to str

Summary

We saw the three basic data types in Python:

int: Integers such as $..., -1, 0, 1, 2, ...$
float: Floating-point numbers such as $-1.2, 3.14,$ etc.
str: Text data (a sequence of characters) such as “hello world”, “Python”, etc.

The terms Object and Value are used interchangeably.
So are the terms Class and Type.