Introduction to Python

by Siddharth Yadav

About Me

  • Python/C++/Go Programmer
  • Working with python and c++ for about 6 years
  • Started working at Synapse in April 2015
  • Xk0nSid anywhere on the internet is me

What is python?

  • A general purpose, interpreted programming language.
  • High level Language
  • Object Oriented
  • Dynamic Typing
  • Cross Platform
  • Created by Guido Von Rossum, a German Computer Scientist in 1991. Currently an employee of Google Inc. working as lead of Google's Python Lab.

Setting up Python

How to get Python?

  • Just go to http://python.org/downloads

What is Python 2 & Python 3?

  • Two stable versions of Python
  • Python 3 was released in 2008
  • Python 3 is not backwards compatible

Which one should you use?

  • Basically can choose anyone
  • Python 3 is new and is the future
  • Python 2 has most support and 3rd party packages

Installing Python

Windows

Just use the windows installer provided by python.org

Linux/Mac OSX

  • It's there already
  • Most linux distros use python for system automation and utilities
  • Mostly Python 2.6
  • It's old
  • Install python using built in package manager
  • Use Homebrew or Mac OSX installer from python.org for Macintosh

Check Python Installation

$ python --version
Python 2.7.8

Just run "python --version" on terminal or command prompt

Python

version 2.7

Python IDLE or Interpreter

  • Integrated DeveLopment Environment
  • Just type "python" in terminal
  • You should see something like this
➜  ~  python                                                                                                                                                                         
Python 2.7.6 (default, Jun 22 2015, 18:00:18) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>

Data in Python

  • Numeric Types
  • Sequences
  • Sets
  • Mappings

Numeric Types

  • int: Integers; equivalent to C longs in Python 2.x, non-limited length in Python 3.x
  • long: Long integers of non-limited length; exists only in Python 2.x
  • float: Floating-Point numbers, equivalent to C doubles
  • complex: Complex Numbers

Sequences

  • str: String; sequence of 8-bit characters in Python 2.x, Unicode characters in Python 3.x
  • byte: a sequence of integers in the range of 0-255; only available in Python 3.x
  • byte array: like bytes, but mutable only available in Python 3.x
  • list
  • tuple

Sets

an unordered collection of unique objects

Mappings (Dictionary)

Python dictionaries, also called hashmaps or associative arrays, which means that an element of the list is associated with a definition

Booleans

  • True
  • False

Mutable Objects

  • byte array
  • list
  • set
  • dict

Immutable

  • int, float, long, complex
  • str
  • bytes
  • tuple
  • frozen set
  • Mutable Objects can be changed after creation.
  • Immutable objects cannot be changed.

Objects

Dive into Code

Control Flow

If Statement

if (condition):
    # block of code
elif (condition):
    # block of code
else:
    # block of code

If statement in python

  • brackets for "conditions" is optional
  • elif is "else if" block
x = [100,200,300]
for i in x:
      print i

For Loop

  • A for loop in python
  • Mostly used with lists or dictionaries
  • Another example of for loop
l = [(1, 1), (2, 4), (3, 9), (4, 16), (5, 25)]
for x, xsquared in l:
    print x, ':', xsquared

While Loop

while (condition):
    # block of code

x = 0

while True:
    if x > 10:
        break
    print x
    x++
  • While loop in python
  • Don't forget to conditionally break loop

Functions

  • A block of code that can be reused
  • Can receive parameters both positional and keyword
  • Can return something(s)
  • A function definition in python
# A function in Python
def say(to, what="Hello"):
    return what + " " + to

Classes

  • Defines a custom object
  • Can receive arguments
  • Can have static and instance method
  • A simple class definition in python
class Hello:

    def __init__(self, to, what="Hello"):
        self.what = what
        self.to = to

    def say(self):
        """This is a public method"""
        print self._build_message()

    def _build_message(self):
        """This is a private method"""
        return self.what + " " + self.to

Modules

  • Bits of reusable code in Python
  • Can be a python file or a folder
  • Can also be DLL, SO, PYD
  • Used with import and from statements 
import math
import socket
import numpy


from hashlib import sha1, md5
from flask import Flask

Dive into Code

Finding Help

  • Documentation at Python.org
  • Using in built Help function
➜  ~  python                                                                                                                                                                         
Python 2.7.6 (default, Jun 22 2015, 18:00:18) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> help(help)

Help on _Helper in module site object:

class _Helper(__builtin__.object)
 |  Define the builtin 'help'.
 |  This is a wrapper around pydoc.help (with a twist).
 |  
 |  Methods defined here:
 |  
 |  __call__(self, *args, **kwds)
 |  
 |  __repr__(self) ...

The End

Introduction to Python

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