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.