In Python we can use integer, floating point and complex numbers

Most arithmetic operations are natively defined in Python.

More complex math functions are defined in the math module

integer numbers

we can use positive and negative integers:

			>>> 42
			42
			>>> -42
			-42
		

floating point numbers

we can use positive and negative floating point numbers

			>>> 3.1234
			3.1234
			>>> -0.255
			-0.255
			>>> .44
			0.44
			>>> -.55
			-0.55
			>>>
		

arithmetic operations

Arithmetic operators @programiz.com

The division operator "/" in python2 returns the integer part(i.e. works like Floor division), while in python3 it returns the float result

Example: arithmetic operations

				>>> 5-3
				2
				>>> 5*3
				15
				>>> 5/3
				1.6666666666666667
				>>> 5//3
				1
				>>> 5%3
				2
		

Example: python3 vs python2 division

			>>> 5/3
			1
		

			>>> 5/3
			1.6666666666666667

			>>> 5//3
			1
		

Python3 adds the "//" operator for Integer division

the math module

math module is native to every python distribution.

to use its functions you only have to import it in your program:

				import math
				# do something with math
			

Example: math functions

			>>> import math
			>>>
			>>> math.pi
			3.141592653589793
			>>> math.floor(math.pi)
			3
			>>> math.pow(2,3)
			8.0
			>>> math.sqrt(9)
			3.0
		

definition

Strings are immutable sequences of Unicode code points (will be discussed further).

Single-line strings literal should be closed in single or double quotes

Multi-line strings literal should be closed in triple single or double quotes

Examples

			>>> "this is a single line string"
			'this is a single line string'

			>>> 'another single line string with UTF charactes like 🍷'
			'another single line string with UTF charactes like 🍷'

			>>> 'but can not be spred in multiple lines
		  File "", line 1
		    'but can not be spred in multiple lines
		                                         ^
			SyntaxError: EOL while scanning string literal
		

Examples

			>>> """infact you can -
			... if you use these triple quotes"""
			'infact you can - \nif you use these triple quotes'

			>>> '''or these triple quotes
			... can separate multiline without errors'''
			'or these triple quotes\ncan separate multiline without errors'


		

concatenation: +

The operation is defined only on string operands:

			#string concatenation with '+':
			>>> "ala" + "bala"
			'alabala

			>>> "1" + "2"
			'12'

			>>> "1" + 3
			Traceback ...
			TypeError: cannot concatenate 'str' and 'int' objects
		

repetition: *

One of the operands must be string, the other - integer

			>>> "-" * 10
			'----------'

			>>> "1" * 10
			'1111111111'

			>>> ">hello<" * 3
			'>hello<>hello<>hello<'

			>>> "a" * "3"
			Traceback ...
			TypeError: can't multiply sequence by non-int of type 'str'
		

String Methods

			# string methods:
			>>> "iva".capitalize()
			'Iva'
		

What a method is will be discussed further!

For now, you can try to look at the docs: String Methods @docs.python.org

What are they?

A names for "containers" (placed in RAM) in which values can be stored

We can set values in a variable, i.e. to write a value into the corresponding container.

We can get the variable value, i.e. to read the content of the corresponding container

example

			x = 99
			y = 3,141516
			first_name = "ada"
			sur_name = "byron"
			num_list = [1,2,3]

			print("x = ", x,)
			print("y = ", y)
			print("first_name = ", first_name)
			print("sur_name = ", sur_name)
			print("num_list = ", num_list)
		

A very simplified view of variables in RAM

Naming Rules

Variables names must start with a letter or an underscore

The remainder of a variable name may consist of letters, numbers and underscores

Names are case sensitive

			_myvar  #OK,
			my_var	#OK
			my-var	# error
			my var 	# error
			myvar_1 # OK
			1myvar	# error
		

Naming conventions

from PEP 8 -- Style Guide for Python Code:

Variable names should be lowercase, with words separated by underscores as necessary to improve readability.

Variable names follow the same convention as function names.

mixedCase is allowed only in contexts where that's already the prevailing style (e.g. threading.py), to retain backwards compatibility.

Why to comment our code?

Python interpreter ignores every part of a program, which is marked as a "comment"

Comments are used to explain and/or summarize a part of our program in a more readable manner

For debugging purposes - when we need fast to ignore a block of code

For other meta information about the program (programme name, author, date, etc.)

A well commented program is more readable and maintainable

How to comment our code?

Single line comment: #

every line which starts with #(hash tag) is a comment and is ignored py Python interpreter

				# this is a just a comment: no print("whatever") will happens
				print("this will be printed, of course")

				### a more semantic example for comment:
				# check if a triangle with sides (3,4,5) is a Pythagorean:
				print(3**2 + 4**2 == 5**2)
			

The problem

Given that:

An astronomical hour consists of 60 minutes

An academical hour consists of 40 minutes

For each 4 academical hours there are 20 minutes brake

Write a Python program, that will print out how many astronomical hours a python course should take, if it consists of 64 academical hours, including the respective brakes

			48.0
		

solution - without variables

			"""
			acad_to_astro_hours.py

			Solution without using variables to store values
			"""

			print((64*40 + 64/4*20)/60)
		

solution: too many variables

			"""
			acad_to_astro_hours_with_vars.py

			An example of too many variables, with too long names.
			"""

			# given:
			minutes_in_astro_hour = 60
			minutes_in_acad_hour = 40
			acad_course_hours = 64
			acad_hours_in_a_partida = 4

			# program logic:
			acad_hours_partidas = acad_course_hours/acad_hours_in_a_partida

			total_minutes_brakes = acad_hours_partidas * 20

			minutes_in_a_course = acad_course_hours * minutes_in_acad_hour + total_minutes_brakes

			course_in_astro_hours = minutes_in_a_course / 60

			print(course_in_astro_hours)




		

HW:acad_to_astro_hours

Write your solution, using your logic and your variables names.

Try to think of a solution, which will be readable enough (# you can use comments) and easy to maintain in future

write your code in a file, named <prefix>_acad_to_astro_hours.py

where <prefix> is your name initials

For instance: iep_acad_to_astro_hours.py

send it to progressbg.python.course@gmail.com

The problem

Calculate your body mass index (BMI) with Python, given the formula:
BMI = W / (H*H)
where:

W = weight_in_kilogram

H = height_in_meters

Your program should outputs the rounded result (to 2 digits from the decimal point). You can use the python's build-in round() function, like:

				>>> round(2.1457, 2)
				2.15

				>>> round(1.4234,2)
				1.42

				>>> round(1.4284,2)
				1.43
			

BMI Categories

What is your BMI category?

solution

			"""
			Solution without using variables to store values,

			and given that W = 53, H = 1.67:
			"""
			print(round(53/(1.67*1.67), 2))

			# 19.0

		

HW: BMI.py

Try to think of a solution, which will be readable enough and easy to maintain in future (you can use comments and semantic variable names)

write your code in a file, named <prefix>_BMI.py

where <prefix> is your name initials

For instance: iep_BMI.py

send it to progressbg.python.course@gmail.com