Python 101

Web Programming Course

SUT • Fall 2018

Outline

  • Introduction

  • Getting Started

  • Python Basics

    • Standard Data Types

    • Operators

  • Control Structures

Introduction

Python

  • Python is an interpreted high-level programming language for general-purpose programming
  • Created by Guido van Rossum and first released in 1991
  • Emphasizes code readability
  • It combines the power of systems languages, such

    as C and Java, with the ease and rapid development of scripting languages, such as Ruby

Language Features

  • Simple and Minimalistic

  • Easy to Learn

  • High-level Language

  • Portable

  • Extensible

  • Embeddable

  • Extensive Libraries

  • Free, Open Source, ... and Fun!

 

 

 

Programming Paradigms

  • Object-Oriented Programming

  • Structured Programming

  • Functional Programming

  • Aspect-Oriented Programming

  • Logic-Programming (by extension)

  • Design-by-Contract (by extension)

 

 

 

Language Philosophy
  • Beautiful is better than ugly

  • Explicit is better than implicit

  • Simple is better than complex

  • Complex is better than complicated
  • Flat is better than nested
  • Sparse is better than dense

  • Readability counts

  • Special cases aren't special enough to break the rules.
    Although practicality beats purity.

Language Philosophy
  • Errors should never pass silently.

    Unless explicitly silenced

  • In the face of ambiguity, refuse the temptation to guess

  • There should be one-- and preferably only one --obvious way to do it.
    Although that way may not be obvious at first unless you're Dutch.

  • Now is better than never

    Although never is often better than *right* now.

  • If the implementation is hard to explain, it's a bad idea.
    If the implementation is easy to explain, it may be a good idea

     

     

     

     

More on Medium

Python 2 VS 3
  • Python 2.0 was released in 2000, with many new

    features added

  • Python 3.0, adjusting several aspects of the core language, was released in 2008

  • Python 3.0 is backwards-incompatible

  • Python 2.x is legacy, Python 3.x is the present and

    future of the language

  • Python porting progress

  • We use Python 3.x in this course

Getting Started

Install

$ sudo apt-get install python3
....

$ python3
% python3
Python 3.6.7rc1 (default, Sep 27 2018, 09:51:25) 
[GCC 8.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.

exit()

$ipython3
 % ipython3 
Python 3.6.7rc1 (default, Sep 27 2018, 09:51:25) 
Type "copyright", "credits" or "license" for more information.

IPython 5.5.0 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.
Python Shell
  • Python's interactive interpreter is one of the most powerful tools used in everyday Python development

  • It enables you to test a few lines of code without
    needing to create, edit, save, and run a source
    file
  • Not only it verifies your code’s correctness, but it
    also enables inspecting data structures or
    altering key values, prior to adding it to your
    source files
Using Shell
  • Python shell evaluates the expression entered
    after prompt and displays the result

In [1]: 2 + 5                                                                                                                                                                                               
Out[1]: 7

In [2]: 2 ** 100                                                                                                                                                                                            
Out[2]: 1267650600228229401496703205376

In [3]: print(3 * 10)                                                                                                                                                                                       
30

In [4]:  

First Program

  • A Python program (or script) is a sequence of
    Python statements that goes into a text file,
    having a .py extension
  • This is our first Python program:
  •  
  • People usually judge the quality of a
    programming language by the simplicity of the
    Hello World! program
print('Hello World!')

Comments

  • Comments in Python are denoted with the hash mark (#)

 

 

 

  • Comments are also used to prevent working
    code from executing
  • Typical usage in configuration files to
    disable/enable options
# hello.py
# By: Behnam Hatami-Varzaneh
print('Hello World!')
# short comment

Python Basics

Variables

  • Python is a dynamically typed language
  • Variables can be thought of as names that refer
    to otherwise anonymous objects, which contain
    the actual values involved
  • Any given variable can have its value altered at
    any time
In [1]: x = 2                                                                                                                                                                                               

In [2]: x                                                                                                                                                                                                   
Out[2]: 2

In [3]: x = 'Ali'                                                                                                                                                                                           

In [4]: x                                                                                                                                                                                                   
Out[4]: 'Ali'

Basic Data Types

  • Boolean
  • Strings
  • Numbers
  • None
In [1]: type(True)                                                                                                                                                                                          
Out[1]: bool

In [2]: type('Hello')                                                                                                                                                                                       
Out[2]: str

In [3]: type(5)                                                                                                                                                                                             
Out[3]: int

In [4]: type(5.2)                                                                                                                                                                                           
Out[4]: float

Operators

  • Basic Operators
    • Arithmetic (+, - , *, /, %, //, **)
    • Assignment (=, +=, -=, *= /=, %=, **= , //=)
    • Comparison (<, >, <=, >=, ==, !=)
    • Logical (and, or, not)
  • Notes:
    • + on strings does string concatenation
    • * on (string, int) repeats string

Type Conversion

  • Python has strong typing (unlike JavaScript)
In [5]: 'Ali' + 0                                                                                                                                                                                           
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-5-877cabd96baa> in <module>
----> 1 'Ali' + 0

TypeError: must be str, not int
  • We need to use type converter functions
In [1]: '123' + str(45)                                                                                                                                                                                     
Out[1]: '12345'

In [2]: int('123') + 45                                                                                                                                                                                     
Out[2]: 168

Input

  • We can use input function to get user input
  • The return value is always a string
In [1]: radius = input('Enter radius: ')                                                                                                                                                                    
Enter radius: 123.5

In [2]: r = float(radius)                                                                                                                                                                                   

In [3]: area = 3.14159 * r ** 2                                                                                                                                                                             

In [4]: print('The area is:', area)                                                                                                                                                                         
The area is: 47916.3160775

Control Structures

Control Structures

  • Conditionals
    • if, else, elif
  • Loops
    • for
    • while

Conditionals

  • Like other languages, Python features if and else
    statements
  • Python’s “else-if” is spelled elif
ans = input("Enter 'y' or 'n': ")
if ans == 'y':
    print("Entered 'y'")
elif ans == 'n':
    print("Entered 'n'")
else:
    print('Invalid key pressed!')

Truth Value Testing

  • Any object can be tested for truth value, for use
    in a condition
  • The following values are considered False
    • None
    • False
    • zero of any numeric type, e.g., 0, 0.0, 0j.
    • any empty sequence or dictionary, e.g., '', (), [], {}
  • All other values are considered True

While Loop

  • The while loop continues to execute the same
    body of code until the conditional statement is
    no longer True
  • We can use break and continue inside the loops
i = 0
while i < 10:
    print(i)
    i += 1

For Loop

  • The for loop in Python is much simpler that other
    C-like languages

 

 

  • We can use range() function to produce a list of
    numbers
for x in ['Ali', 'Mahsa', 'Navid', 'Zahra']:
    print('Hello ' + x + '!')
for i in range(10):
    print(i)

Title Text

Python 101

By Behnam Hatami

Python 101

python / Web Programming Course @ SUT, Fall 2018

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