1. Overview of Python

1.1. Comments

A computer program is intended to be understood by both humans and computers. However to make it easier for the humans, it can also contain comments written in English.

# A comment looks like this

Python ignores comments. They provide explanations for the human readers.

1.2. Literals

A Python program can contain any number and any string of text surrounded by quotes.

Examples:

5

1.23

“Hello”

‘Barry’

1.3. Keywords

Every computer language has a number of keywords that you will need to learn along with their meanings. Fortunately they look like English words and there are only a few of them in Python. You could tick them off as you meet them.

False	None	True	and	as	assert	async	await
break	class	continue	def	del	elif	else	except
finally	for	from	global	if	import	in	is
lambda	nonlocal	not	or	pass	raise	return	try
while	with	yield

1.4. Built-ins

Python also comes with a large number of functions. The most common ones are built-in and always available, much like the keywords. Here is a list of them, just for the sake of completeness, but you probably won’t ever use them all, and when you do use one you will probably look it up in the documentation. So you don’t need to remember these.

abs	all	any	ascii	bin	bool
breakpoint	bytearray	bytes	callable	chr	classmethod
compile	complex	copyright	credits	delattr	dict
dir	divmod	enumerate	eval	exec	exit
filter	float	format	frozenset	getattr	globals
hasattr	hash	help	hex	id	input
int	isinstance	issubclass	iter	len	license
list	locals	map	max	memoryview	min
next	object	oct	open	ord	pow
print	property	quit	range	repr	reversed
round	set	setattr	slice	sorted	staticmethod
str	sum	super	tuple	type	vars
zip

Once you understand all of these you effectively understand all of the Python language. By the end of this book you will be familiar with at least 20 keywords / functions which is enough to create a huge variety of programs.

1.5. Libraries

There are many more functions available (too many to list here), but not everyone will need them, so they are kept in libraries. Some libraries are supplied with Python. You can use their functions only after first importing the relevant library module. For example, if you want a random number, import the random library:

from random import randint
print(randint(0,10))

Other libraries are not supplied with Python and must be downloaded separately, such as the Minecraft, Pygame and RLZero libraries.

1.6. Names

You will see many words in a program that appear to be English words and yet they are not literals, keywords or library functions. These are names chosen by the programmer. For example, if the program needs to record a score and store it in a variable, the programmer might choose to give that variable the name score:

score = 1
print("Score: ", score)

Python has no understanding of what score means. It only cares that the same word is used every time. So a different programmer might decide to write the program like this:

points = 1
print("Score: ", points)

A programmer who doesn’t like typing might use a shorter, less descriptive name:

p = 1
print("Score: ", p)

However the programmer must be consistent. This would not work:

points = 1
print("Score: ", score)

1.7. Whitespace

Python is unusual in that it cares about whitespace, i.e. what you get when you press the tab key or the space bar on the keyboard.

Python programs are arranged in blocks of lines. Every line in a block must have the same amount of whitespace preceding it - the indentation. See Program 2.19 for an example.