Python Primer

https://www.python.org/doc/essays/blurb/

What is Python? Executive Summary

Python is an interpreted, object-oriented, high-level programming language with dynamic semantics. Its high-level built in data structures, combined with dynamic typing and dynamic binding, make it very attractive for Rapid Application Development, as well as for use as a scripting or glue language to connect existing components together. Python's simple, easy to learn syntax emphasizes readability and therefore reduces the cost of program maintenance. Python supports modules and packages, which encourages program modularity and code reuse. The Python interpreter and the extensive standard library are available in source or binary form without charge for all major platforms, and can be freely distributed.

Why use Python?

1) Readable and Maintainable Code

2) Multiple Programming Paradigms (object oriented and structured programming fully) dynamic type system,  and automatic memory management) 3) Compatible with Major Platforms and Systems

4) Robust Standard Library

5) Many Open Source Frameworks and Tools

6) Simplify Complex Software Development

7) Adopt Test Driven Development

sudo apt update

sudo apt install python3 python3-dev python3-venv

wget https://bootstrap.pypa.io/get-pip.py

sudo python get-pip.py

mkdir project

cd project

Run a Python Script Under Mac, Linux, BSD, Unix, etc

On platforms like Mac, BSD or Linux (Unix) you can put a "shebang" line as first line of the program which indicates the location of the Python interpreter on the hard drive. It's in the 

following format:

Pull examples from github

john@cloudshell:~ (my-email-api-tor)$git clone  https://github.com/jiacovacci/py_exam.git

                                                                

Cloning into 'py_exam'...

remote: Enumerating objects: 3, done.

remote: Counting objects: 100% (3/3), done.

remote: Compressing objects: 100% (2/2), done.

remote: Total 3 (delta 0), reused 3 (delta 0), pack-reused 0

Unpacking objects: 100% (3/3), done.

john@cloudshell:~ (my-email-api-tor)$

 

Hello World

 

!/usr/bin/python3

# Say hello, world.

print ("Hello, world!")

 

Python has the following data types built-in by default, in these categories:

 

 

python program dt.py

 

#!/usr/bin/python3

# DATA TYPE Examples

 

 

########## INTEGER #######################

my_int = 5

print(type(my_int))

print(my_int)

 

########### FLOAT ########################

 

my_float = 20.5

print(type(my_float))

print(my_float)

 

########## LISTS #################

List is a collection which is ordered and changeable. Allows duplicate members.

 

my_list = [1,2,3]

for it_name in my_list:

    print (it_name)

print(type(my_list)

 

########## DICTIONARY #################

Dictionary is a collection which is unordered, changeable and indexed. No duplicate members.

 

 

my_dict = {"name" : "John", "email" : "john.iacovacci1@gmail.com"}

print (my_dict['name'])

print(type(my_dict))

 

########### BOOL ###########

### BOOLEAN ###

Booleans represent one of two values: True or False.

 

x = True

 

#display x:

print(x)

 

#display the data type of x:

print(type(x)) 

 

Python Arithmetic Operators

 

python program ao.py

 

#!/usr/bin/python3

 

# DATA OPERATOR EXAMPLES ##########

 

### Arithmetic Operators ###

### ADD ###

x = 2 + 3

print('ADD x = 2 + 3')

print(x)

 

### SUBTRACT ###

print('SUBTRACT x = 3 -2')

x = 3 -2

print(x)

 

### MULTIPLY ###

print('MULTIPLY x = 3 * 2')

x = 3 * 2

print(x)

 

### DIVISION ###

print('DIVIDE x = 3 / 2')

x = 3 / 2

 

### MODULUS ###

print('MODULUS x = 5 % 2')

x = 5 % 2

print(x)

 

### EXPONENTIAL ###

print('EXPONENTIAL x = 3**2')

x = 3**2

print(x)

 

Python Assignment Operators

 

python program ao.py

 

#!/usr/bin/python3

 

#!/usr/bin/python3

### Assignment Operators ###

print('= sign  x = 3')

x = 3

print(x)

 

print('+= sign  x += 3')

x = 6

x += 3

print(x)

 

print('-= sign  x-= 3')

x = 6

x -= 3

print(x)

 

print('*= sign  x*= 3')

x = 6

x *= 3

print(x)

 

print('/= sign  x/= 3')

x = 6

x /= 3

print(x)

 

Python Comparison Operators

 

python program co.py

 

#!/usr/bin/python3

 

### Comparison Operators ###

print('== sign, x = 3, y = 5,  is x == y')

x = 3

y = 5

print(x == y)

 

print('!= sign, x = 3, y = 5,  is x != y')

x = 3

y = 5

print(x != y)

 

print('> sign, x = 3, y = 5,  is x > y')

x = 3

y = 5

print(x > y)

 

print('< sign, x = 3, y = 5,  is x < y')

x = 3

y = 5

print(x < y)

 

print('>= sign, x = 3, y = 5,  is x >= y')

x = 3

y = 5

print(x > y)

 

print('<= sign, x = 3, y = 5,  is x <= y')

x = 3

y = 5

print(x <= y)

 

Python Logical Operators

 

python program lo.py

 

#!/usr/bin/python3

 

### Logical Operators ###

 

print('and operator , x = 5, x > 3 and x < 10')

x = 5

print(x > 3 and x < 10)

 

print('or operator , x = 5, x > 3 or x < 4')

x = 5

print(x > 3 or x < 4)

 

print('not operator , x = 5, not(x > 3 or x < 10)')

x = 5

print(not(x > 3 and x < 10))

 

String format()

The format() method allows you to format selected parts of a string.

Sometimes there are parts of a text that you do not control, maybe they come from a database, or user input?

To control such values, add placeholders (curly brackets {}) in the text, and run the values through the format() method:

python program pf.py

 

#!/usr/bin/python3

 

 

### FORMAT ###

 

 

print('This is a String {}'.format('INSERTED'))

 

 

price = 49

txt = "The price is {:.2f} dollars"

print(txt.format(price))

 

 

quantity = 3

itemno = 567

price = 49

myorder = "I want {} pieces of item number {} for {:.2f} dollars."

print(myorder.format(quantity, itemno, price))

 

 

quantity = 3

itemno = 567

price = 49

myorder = "I want {0} pieces of item number {1} for {2:.2f} dollars."

print(myorder.format(quantity, itemno, price))

 

 

 

Python Lists

 

 

Python Lists

 

Python Collections (Arrays)

There are four collection data types in the Python programming language:

• List is a collection which is ordered and changeable. Allows duplicate members.

• Tuple is a collection which is ordered and unchangeable. Allows duplicate members.

• Set is a collection which is unordered and unindexed. No duplicate members.

• Dictionary is a collection which is unordered, changeable and indexed. No duplicate members.

python program lt.py

 

#!/usr/bin/python3

 

### List Example ###

print('loop thru list')

my_list = ['d','e','f','a','b']

for it_name in my_list:

    print (it_name)

 

### RANGE ###

print('range starting at position 2 upto but not including position 4')

print(my_list[2:4])

 

#Remember that the first item is position 0,

#and note that the item in position 4 is NOT included

 

### REPLACE ITEM ###

 

print('replace position 1 with z')

 

my_list[1] = 'z'

print(my_list)

 

### LENGTH ###

 

print('length of list')

 

print(len(my_list))

 

### SORT METHOD ###

 

print('sort the list')

my_list.sort()

 

print(my_list)

 

### TUPLE ###

 

print('loop thru tuple')

my_list = ('d','e','f','a','b')

for it_name in my_list:

    print (it_name)

 

########## DICTIONARY #################

 

print('dictionary example')

 

x = {"name" : "John", "email" : "john.iacovacci1@gmail.com"}

print (x['name'])

print(type(x))

 

 

Python Control Flow

 

python program cf.py

 

#!/usr/bin/python3

 

### CONTROL FLOW ###

 

### if test ###

 

a = 3

b = 5

print('if a = 3 and x = 5')

if b > a:

  print("b is greater than a")

 

### if elif test ###

 

a = 6

b = 5

print('elsif a = 6 and x = 5')

if b > a:

   print("b is greater than a")

elif a > b:

    print("a is greater than b")

 

### if elif else test ###

 

a = 5

b = 5

print('else a = 5 and x = 5')

if b > a:

   print("b is greater than a")

elif a > b:

   print("a is greater than b")

else:

       print("a is equal to b")

 

 

### FOR NEXT ###

 

print('for next loop')

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

for it_name in my_list:

    print (it_name)

 

### looping thru a string ###

print('looping thru string')

 

for x in "orange":

  print(x)

 

print('fomatting loop thru string')

 

index_count = 0

for letter in 'orange':

  print('At index {} the letter is {}'.format(index_count,letter))

  index_count += 1

 

### while loops ###

print('while loop')

 

i = 1

while i < 5:

  print(i)

  i += 1

 

 

### while loop break ###

print('while loop break')

 

i = 1

while i < 5:

  print(i)

  if i == 3:

    break

  i += 1

 

 

Python User Input

 

 

 

python program ui.py

 

 

#!/usr/bin/python3

### USER INPUT ###

 

 

my_name = input("What is your name?:")

print("My name is: " + my_name)

 

 

 

Python Functions

A function is a block of code which only runs when it is called.

You can pass data, known as parameters, into a function.

A function can return data as a result.

Allows developers to build blocks of repeatable code.

starts with def

In Python a function is defined using the def keyword:

def name_of_function(name):

      Block of code

Arguments

Information can be passed into functions as arguments.

Return Values

Return allows variables to be set and return values within functions.

Arbitrary Arguments, *args

If you do not know how many arguments that will be passed into your function, add a * before the parameter name in the function definition.

Keyword Arguments

You can also send arguments with the key = value syntax.

This way the order of the arguments does not matter.

Arbitrary Keyword Arguments, **kwargs

If you do not know how many keyword arguments that will be passed into your function, add two asterisk: ** before the parameter name in the function definition.

This way the function will receive a dictionary of arguments, and can access the items accordingly:

python program functions.py

#!/usr/bin/python3

 

### SIMPLE FUNCTION ###

 

def my_function():

  print("Hello World")

 

my_function()

 

### FUNCTION WITH AN ARGUMENT ###

def name_function(name):

    print("My name is " +name)

 

name_function("John Iacovacci")

 

 

### RETURN VALUE FROM FUNCTION ###

def my_function(x,y):

  return  x * y

 

print(my_function(3,5))

 

### FUNCTION WITH X ARGS ###

def my_function(*kids):

  print("The youngest child is " + kids[1])

 

my_function("Jonathan","Michael")

 

### FUNCTION WITH KEY WORD ARGUMENTS ###

 

def my_function(child2, child1):

  print("The youngest child is " + child2)

 

my_function(child1 = "Jonathan", child2 = "Michael")

 

### ARBITARY KEY WORD ARGUMENTS ###

 

def my_function(**kid):

  print("His last name is " + kid["lname"])

 

my_function(fname = "Jonathan", lname = "Iacovacci")

 

Python Classes and Objects

 

 

Python is an object oriented programming language.

 

Almost everything in Python is an object, with its properties and methods.

 

A Class is like an object constructor, or a "blueprint" for creating objects.

 

Create a Class

To create a class, use the keyword class:

 

OOP Object oriented programming allows developers to create their own objects that have methods and attributes.

 

call methods using .methond_name() syntax

 

Methods act as functions that use information about the object, as well as the object itself to return results, or change the current object.

 

OOP allows us to create code that is repeatable and organized

 

class NameOfClass():

      def __init__(self,param1,param2):

            self.param1 = param1

            self.param2 = param2

       def some_method(self):

            # perform some action

            print(self.param1)

python program class.py

 

#!/usr/bin/python3

### Class Examples ###

 

 

class Sample():

    pass

 

 

my_sample = Sample()

 

 

print(type(my_sample))

__init__ method

"__init__" is a reseved method in python classes. It is called as a constructor in object oriented terminology. This method is called when an object is created from a class and it allows the class to initialize the attributes of the class

 

What is the __ main __ in Python?

'__main__' is the name of the scope in which top-level code executes. Basically you have two ways of using a Python module: Run it directly as a script, or import it. When a module is run as a script, its __name__ is set to __main__

 

Python self

Featured snippet from the web

self in Python class. self represents the instance of the class. By using the “self” keyword we can access the attributes and methods of the class in python. It binds the attributes with the given arguments. The reason you need to use self.

 

 

 

 

 

 

 

 

python program class_dog.py

#!/usr/bin/python3

### Class Examples ###

 

 

class Dog():

    def __init__(self,breed):

        self.breed = breed

 

 

my_dog = Dog(breed='Lab')

 

 

print(type(my_dog))

 

 

print(my_dog.breed)

python program class_doggy.py

 

#!/usr/bin/python3

### Class Examples Methods ###

 

 

class Dog():

    species = "mammal"

    def __init__(self,breed,name):

        #assign using self.attribute_name

        self.breed = breed

        self.name = name

 

 

    #methods ...actions

    def bark(self):

        print("WOOF!")

 

 

my_dog = Dog(breed='Lab',name="Bear Bear")

 

 

print(type(my_dog))

 

 

print(my_dog.breed)

print(my_dog.name)

 

 

my_dog.bark()

 

https://wiki.python.org/moin/BeginnersGuide/Programmers

Assignment number 4

Built an invoice program for you web site to calculate items people buy.

E.g.

#!/usr/bin/python3

# DATA TYPE Examples

 

 

########## DICTIONARY #################

 

cust_name =    input("Customer name: ")

cust_address = input("      Address: ")

cust_city =    input("         City: ")

cust_state =   input("        State: ")

cust_zip =     input("          Zip: ")

print(cust_name)

print(cust_address)

items = {"plates" : 3, "cups" : 1, "glasses" : 2}

for x in items:

      print(x, items[x])

no_plates =  input("Number of  Plates: ")

no_cups =    input("Number of    Cups: ")

no_glasses = input("Number of Glasses: ")

total_plates =  int(no_plates) * int(items["plates"])

total_cups =    int(no_cups) * int(items["cups"])

total_glasses = int(no_glasses) * int(items["glasses"])

total_charge = int(total_plates) + int(total_cups) + int(total_glasses)

print(cust_name)

print(cust_address)

print(cust_city)

print(cust_zip)

 

print(total_charge)

myplates = "You Bought {} number of plates at {} = {} dollars."

print(myplates.format(no_plates, items["plates"], total_plates))

mycups = "               {} number of cups at {} = {} dollars."

print(mycups.format(no_cups, items["cups"], total_cups))

myglasses = "         {} number of glasses at {} = {} dollars."

print(myglasses.format(no_glasses, items["glasses"], total_glasses))

mytotal = "                   Total Amount Due = {} dollars."

print(mytotal.format(total_charge))

https://github.com/jiacovacci/assign4.git

git clone  https://github.com/jiacovacci/assign4.git