COMP1531

🔨 Python

1.3 - Introduction

 

Author: Hayden Smith 2021

In this lecture

Why?

  • Python is a valuable tool to learn and necessary for the project

What?

  • Learning a second language
  • Python vs C
  • Core python language features
  • Python versions

 

Python is a high level scripting language with rich libraries that has common applications in building simple services, utility tools, and all forms of data science.

 

Python is the universal go-to language if you had to pick up just one programming language.

 

def times_tables(size):
    lst = []
    for i in range(size):
        for j in range(size):
            lst.append(f"{i} * {j}")
    return lst
  • Rapidly build applications due to high level nature
  • Very straightforward toolchain to setup and use
  • It's very structured compared to other scripting languages
  • Useful in data science and analytics applications

Why Python?

Learning another programming language is a very comfortable exercise, particularly if the language is from the same programming paradigm.

 

Other major factors dictate differences between languages - i.e. does it deal with pointers? Is it a typed language?

Learning another language

Procedural Object-oriented Typed Pointers Compiled
C Yes No Yes Yes Yes
C++ Yes Yes Yes No Yes
Java No Yes Yes No Yes
Python Yes Yes Can be No No
Javascript Yes Yes Can be No No

Of course, there are syntax differences! But syntax differences are easy to pick up.

 

In the case of learning another language like Python, the main hurdles we have to overcome are:

  • Python does not have types, unlike C
  • Python has object-oriented components (which we can somewhat ignore), unlike C
  • Python does not deal with pointers, unlike C (yay)
  • Python is often written at a "higher level" (more abstract)
  • Python does not have an intermediate compilation step, like C

 

Learning another language

Python vs C

def add_two_numbers(one, two):
    three = one + two
    return [ one, two, three ]
int add_two_numbers(int one, int two) {
    int three = one + two
    int *arr = malloc(sizeof(int) * 3);
    arr[0] = one;
    arr[1] = two;
    arr[2] = three;
    return arr;
}

Python

C

Write a function that takes two numbers, and returns a list of those two numbers along with its sum

Python vs C

Interpreted V compiled

C program

Python program

Machine Code

Output

Output

Compile

Run

Compile & Run

Because you already know C, we will teach Python very quickly and mainly focus on the differences between Python and C.

 

Unlike C, Python has a sprawling set of capabilities - the language will feel much bigger, and therefore you might feel you have a poorer grasp on it.

 

Don't expect to know everything about Python this term. Just focus on only learning what you need to solve a problem at hand, and you will learn more super quick.

 

Read more about the python language here.

Learning Python

Python can be run via the command line directly without compiling:

Python

$ python3 myfile.py
print("Hello world!")

myfile.py

name = "Giraffe"
age = 18
height = 2048.11 # mm

num1 = 3 ** 3
num2 = 27 // 3

print("=== Printing Items ===")
print(name + ", " + str(age) + ', ' + str(height))
print(name, age, height, sep = ', ')
print(f"{name}, {age}, {height}")

print("=== Printing Types ===")
print(type(name))
print(type(age))
print(type(height))

print("=== Printing Mixed ===")
print(f"3 ** 3 == {num1}")
print(f"27 // 3 == {num2}")

Python - Basics

types.py

  sentence = "My"
  sentence = sentence + " name is"
  sentence += " Pikachu"

  print(sentence)

  print("Hi!!" * 10)

Python strings are immutable

Python - Strings

strings.py

# This is a list
names = ['Hayden', 'Jake', 'Nick', 'Emily']
print(f"1 {names}")
print(f"2 {names[0]}")
names[1] = 'Jakeo'
names.append('Rani')
print(f"3 {names}")

print('====================================')

# This is a tuple
animals = ('Giraffe', 'Turtle', 'Elephant')
print(f"4 {animals}"
print(f"4 {animals[0]}"
# animals[1] = 'Dog' PROHIBITED
animals.append('Koala')

[Lists] are for mutable ordered structures of the same type

[Tuples] are for immutable ordered structures of any mix of types

Python - Lists & Tuples

lists-tuples.py

chars = ['a', 'b', 'c', 'd', 'e']

## Normal Array/List stuff
print(chars)
print(chars[0])
print(chars[4])

## Negative Indexes
print(chars[-1])

## Array Slicing
print(chars[0:1])
print(chars[0:2])
print(chars[0:3])
print(chars[0:4])
print(chars[0:5])
print(chars[2:4])
print(chars[3:5])
print(chars[0:15])
print(chars[-2:-4])

Lists/Tuples can be "sliced" to extract a subset of information about them. This is a real standout feature of python.

Python - Slicing

slicing.py

# Note the following:
#  - Indentation and colon denotes nesting, not braces
#  - Conditions generally lack paranthesis
#  - pass used to say "do nothing"
#  - i++ is not a language feature

number = 5
if number > 10:
	print("Bigger than 10")
elif number < 2:
	pass
else:
	print("Number between 2 and 9")

print("--------------------------")

i = 0
while i < 5:
	print("Hello there")
	i += 1

print("--------------------------")
for i in range(5):
	print("Hello there")

Python - Control Structures

control-structures.py

def get_even(nums):
	evens = []
	for i in range(len(nums)):
		if number % 2 == 0:
			evens.append(number)
	return evens

all_numbers = [1,2,3,4,5,6,7,8,9,10]
print(get_even(all_numbers))

Python - Functions

functions.py

student = {
    'name': 'Emily',
    'score': 99,
    'rank': 1,
}

print(student)
print(student['name'])
print(student['score'])
print(student['rank'])

student['height'] = 159
print(student)

Python - Dictionaries

dictionaries.py

Think of dictionaries like structs. You use them when you need a "collection" of items that are identified by a string description, rather than a numerical index (lists)

student1 = { 'name' : 'Hayden', 'score': 50 }
student2 = { 'name' : 'Nick', 'score': 91 }
student3 = { 'name' : 'Emily', 'score': 99 }
students = [student1, student2, student3]

print(students)

# Approach 1
num_students = len(students)
for i in range(num_students):
  student = students[i]
  if student['score'] >= 85:
    print(f"{student['name']} got an HD")

# Approach 2
for student in students:
  if student['score'] >= 85:
    print(f"{student['name']} got an HD")

Python - Combining

combining1.py

It's possible to create data structures of other data structures

Versions

python2

python3

Python

In COMP1531, we will be using python 3.7 for everything.

 

If you're on the CSE machines, you can run the python interpreter with "python3" - this will automatically use python3.7

 

If you're on a local machine, we recommend you run python with "python3.7" - this will ensure you use the right version

Python

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COMP1531 21T3 - 1.3 - Python - Intro

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