#!/usr/bin/env python
# coding: utf-8

# # 2. Values, expressions and statements
# 
# <a href="https://colab.research.google.com/github/rambasnet/FDSPython-Notebooks/blob/master/Ch02-Data-Variables.ipynb" target="_parent"><img src="https://colab.research.google.com/assets/colab-badge.svg" alt="Open In Colab"/></a>
# 
# 
# - http://openbookproject.net/thinkcs/python/english3e/variables_expressions_statements.html
# 
# ## Topics
# - data values and types
# - variables
# - expressions and statements
# - numeric operators and basic computations
# - order of operations
# - standard input and output
# - type casting
# - Composition and algorithm
# 
# ## 2.1 Values and data types
# - a value is one of the fundamental things or data -- like a letter or number -- that a program manipulates 
# - these values are clssified into types
# - Python fundamentally supports two major data types: numbers and strings
# - Boolean (True/False) is also supported type
# 
# ### Numbers
# - Integer (int) 
#     - +/- whole numbers: 199, -98, 0
# - Float 
#     - +/- real numbers - numbers with decimal points: 99.99, -0.01
# 
# 
# ### Strings
# - Python uses **str** abbreviation for String type
# - strings are one or more characters represent using single, double or tripple quotes

# ## 2.2 First program - hello world!

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#----------------------------------------------------------
# hello world program
# by: John Doe
# Jan 1, 2017
# Copyright: Anyone may freely copy or modify this program
#----------------------------------------------------------
print('hello world!') # say hello to the beautiful world!
# In python 2: print is a statement not a function
# print 'Hello World!' 


# ## 2.3 Comments
# - Programming languages provide a way to write comment along with the codes
# - Python uses \# symbol to write a single line comment
# - comments are for humans/programmers to convey/explain what the code is doing or supposed to do
# - Python interpreter ignores the comments

# ## 2.4 Data Types
# - built-in type() function can be used to know type of data
# - functions will be covered in Chapter 04

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type(100)


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type(-9)


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type(1000.99345435)


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type(-2.345)


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type('Hello World!')


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type('A')


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print("hello")


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type("17")


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type("""Triple double quoted data""")


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type('''Type of Triple single quote data is''')


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a = "hello"


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a


# ## 2.5 Type conversion/casting
# - data needs to be converted from one type to another as needed
# - the process is called type casting
# - use built-in functions such as str(), int() and float()
# - **str(value)** - converts any value into string
# - **int(value)** - converts numeric value into int
# - **int(value)** - converts numeric value into float

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data = 'hello' # can't conver it to int or float types


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type(data)


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data = '100'
type(data)


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data


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num = int(data)
type(num)


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num


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price = float('500.99')
type(price)


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float('hi')


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num = 99.99
strNum = str(num)
type(strNum)


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type(True)


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type(False)


# ## 2.6 Statements
# - a **statement** is an instruction that the Python interpreter can execute
# - we've seen assignment statements so far
# - we'll later explore for, if, import, while and other statements

# ## 2.7 Expressions
# - an **expression** is a combination of values, variables, operators, and calls to functions
# - expressions are evaluated giving a results

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1+2


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len('hello')


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print(2+3*4)


# ## 2.8 Standard Output
# - printing or writing output to common/standard output such as monitor
# - way to display the results and interact with the users of your program
# - use print() function

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print('''"Oh no", she exclaimed, "Ben's bike is broken!"''')


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print(34.55)


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print(2+2)


# ## 2.9 Escape Sequences
# - some letters or sequence of letters have special meaning to Python
# - single, double and tripple single or double quotes represent string data
# - use backslash \\ to represent these escape sequences, e.g.,
#     - \\n - new line
#     - \\\\ - back slash
#     - \\t - tab
#     - \\r - carriage return
#     - \\' - single quote
#     - \\" - double quote

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print('What\'s up\n Shaq O\'Neal?')


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print('hello \there...\n how are you?')


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print('how many back slahses will be printeted? \\\\')


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print(r'how many back slahses will be printeted? \\\\')


# ## 2.10 Variables
# - variables are identifiers that are used to store values which can be then easily manipulated
# - variables give names to data so the data can be easily referenced by their names over and again
# - rules and best practices for creating identifiers and variable names:
#     - can't be a keyword -- what are the built-in keywords?
#     - can start with only alphabets or underscore ( _ )
#     - can't have symbols such as $, %, &, white space, etc.
#     - can't start with a digit but digits can be used anywhere else in the name
#     - use camelCase names or use _ for_multi_word_names
#     - use concise yet meaningul and unambigous names for less typing and avoid typos

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help('keywords')


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# variable must be defined/declared before you can use
print(x)


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x = 'some value'


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print(x)


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# Exercise: Define a bunch of variables to store some values of different types
var1 = -100
num = -99.99
name = 'John'
lName = 'Smith'
MI = 'A'
grade = 10.5
Name = 'Jake'
grade = 19.9


# ## 2.11 Dynamic Typing
# - type of variables are dynamically evaluated in Python when the assignment statement is executed
# - same variable can be uesd to hold different data types

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var = 100


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var = 'hello'


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var = 99.89


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var


# ## 2.12 Visualize variable assignments in pythontutor.com
# [Click Here](http://pythontutor.com/visualize.html#code=var1%20%3D%20100%0Anum%20%3D%2099.99%0Aname%20%3D%20'John'%0AlName%20%3D%20'Smith'%0AMI%20%3D%20'A'%0Agrade%20%3D%2010.5%0Agrade%20%3D%2019.9%0AName%20%3D%20'Jake'&cumulative=false&curInstr=0&heapPrimitives=false&mode=display&origin=opt-frontend.js&py=3&rawInputLstJSON=%5B%5D&textReferences=false)

# ## 2.13 Computation - operators and operands
# - **operators** are special tokens/symbols that represent computations like addition, multiplication and division 
# - the values an operator uses are called **operands**
# - some binary operators that take two operands
#     - addition: 10 + 20
#     - subtraction: 20 - 10 
#     - true division: 10 / 3
#     - multiplication: 7 * 9
#     - integer division: 10 // 3
#     - remainder or modulus operator: 10 % 2
#     - power: 2 ** 3

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# Exercise: play with some examples of various operators supported by Python


# ## 2.14 Order of operations
# - depends on the rules of precedence
# 
# **uses PEMDAS rule from high to low order**
# 
# 1. Parenthesis
# 2. Exponentiation
# 3. Multiplication and Division (left to right)
# 4. Addition and Subtraction (left to right)
# 

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# some examples
print(2 * 3 ** 2)


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x = 1
y = 2
z = 3
ans = x+y-z*y**y
print(ans)


# ## 2.15 Operations on strings
# - $+$ and $*$ operators also work on strings
# - Chapter 08 covers more on string data type and operations

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# some examples
fname = "John"
lname = "Smith"
fullName = fname + lname
print(fullName)


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gene = "AGT"*10


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print(gene)


# ## 2.16 Standard input
# - read data from standard or common input such as keyboards
# - allows your program to receive data during program execution facilitating user interactions
# - input values will have type string even if numbers are entered
# - use variables to store the data read from standard input

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name = input('What is your name? ')


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print('hello,', name)


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num = input('Enter a number =>')
print('You entered: ', num)
print('type of', num, '=', type(num))


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num


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# str must be casted into int or float depending on the value required
num = int(num)
print('type of', num, '=', type(num))


# ## 2.17 Composition
# - break a problem into many smaller sub-problems or steps using high-level algorithm steps
# - incrementally build the solution using the sub-problems or steps

# ## 2.18 Algorithm
# - step by step process to solve a given problem
#     - like a recipe for a food menu
# - what are the steps you'd give a martian to buy grocery on earth?
#     1. Make a shopping list 
#     - Drive to a grocery store
#     - Park your car
#     - Find items in the list
#     - Checkout
#     - Load grocery
#     - Drive home

# ## 2.19 Exercises

# ### 1. area and perimeter of a rectangle
# 
#  - write a python script that calculates area and perimeter of a rectangle

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# Demonstrate composition step by step
# Algorithm steps
# 1. Get length and width of a rectangle
#     a. hard coded values OR
#     b. prompt user to enter length and width values
#        i. convert length and width into right data types
# 2. Find area = length x width
# 3. Find perimeter = 2(length + width)
# 4. Display calculated results


# ### 2. area and circumference of a circle
# - write a python script that calculates area and circumference of a circle
# - area of a circle is calculated using equation: $\pi r^{2}$
# - perimeter of a circel is calculated using equation: $2 \pi r$
# - you can use $\pi=3.14159$

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# Demonstrate composition step by step
# Algorithm steps


# ### 3. Body Mass Index (BMI)
# - write a python script that calculates BMI of a person
# - BMI is body mass in kg divided by the square of body height in meter with the units of $kg/m^2$
# - https://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmicalc.htm

# ### 4. area and perimeter of a triangle
# - write a python script that finds area and perimeter of a triangle given three sides
# - Hint: Google and use Heron's formula to find area of triangle

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