Python - Why should you learn?

Thamme Gowda

Feb 9th, 2018. SJCIT

Hello World

World's simplest hello world program



In [11]:

    
print("Hello World")









    



Hello World

Two major version branches

Python 2.x
- Latest: 2.7.x
Python 3.x
- Latest: 3.6.x

Python 3.x is not backward compatible with python 2.x.

In Python 2.x

print "Hello World" # print is a keyword

In Python 3.x

print("Hello World") # print is a built in function

I strongly recommend you to use 3.x.

When a programmer submitted HW essay

How python programmer learned to fly

Huge Collection of Existing Libraries

get any library from repositories

High level ?

More english like (as high as we could get!)
Not a joke! Python code is 'executable pseudo code'

Interpreted

You DONT NEED TO compile code (to the machine language)
- but if you want to (for performance reasons), you CAN!
python command runs an interpreter on your python code
- converted to machine instructions at run time (of course!)
So, no more compile time errors! Is it good or bad?
- Bad ? Write test cases

Dynamic Typed

What is a type?
What is a cast or (type) casting? - We dont have worry in python!



In [44]:

    
# sample function
def add(op1, op2):
    return op1 + op2

# Integers
var1 = 10
var2 = 20
var3 = add(var1, var2)
print(var3)

# Floats
var1, var2 = 1.5, 2.6 # multiple assignment
print(add(var1, var2))

# Strings
var1 = "ABCD"
var2 = "EFGH"
var3 = add(var1, var2)
print(var3)
print(">> With great power comes great responsibility!")









    



30
4.1
ABCDEFGH
>> With great power comes great responsibility!

Mis-Conceptions

python does not have types?
- No! Python does have types, but they are dynamic



In [12]:

    
x = "Hello"
print(type(x))
x = 10
print(type(x))
x = 1e10
print(type(x))
x = True
print(type(x))
x = None
print(type(x))









    



<class 'str'>
<class 'int'>
<class 'float'>
<class 'bool'>
<class 'NoneType'>

Automatic Memory Management

Look for this:

No new keyword (as in C++ or Java), no malloc calloc (as in C)
No need to call free (as in C) or delete (as in C++)
- Just like Java, when you lose a reference to memory, garbage collector will mark it for cleaning



In [40]:

    
class User(object):

    def __init__(self, name, email):
        self.name = name
        self.email = email


u1 =  User(name="TG", email="tg@isi.edu")
print(u1.name, u1.email)
u1 = None # in python equivalent of NULL is None
print(u1)
# GC will free the above object when it needs memory









    



TG tg@isi.edu
None

General Purpose

Here are some libraries I have used

Web applications and API Services : Django, Flask,
Windowing Applications: PyQt, TkInter, PyGTK, PyKDE, Py
Operating system tools / Commandline : sys, os, argparse, subprocess modules
Machine Learning / Deep learning: scikit-learn, tensorflow, keras, pytorch, libSVM,
Scientific Computing: scipy
Text processing / Natural Language Processing: nltk, spacy
Linear Algebra: numpy
Data processing/ ETL: pandas,
Visualizations: Matplotlib
Distributed and parallel computing: py-spark
GPUs: py-cuda
...

Obtaining and using libraries:

use conda or pip to search and install libraries (also called modules)
- Look for miniconda and install it to your system
- then you can use conda install [lib_name]
- example: conda install numpy
use import keyword to enable a module in your program



In [41]:

    
import json

u1 =  User(name="TG", email="tg@isi.edu")
print(json.dumps(u1.__dict__))

# or, another way
®®from json import dumps
print(dumps(u1.__dict__))

# aliasing, yet another way 
from json import dumps as to_json
print(to_json(u1.__dict__))









    



{"name": "TG", "email": "tg@isi.edu"}
{"name": "TG", "email": "tg@isi.edu"}
{"name": "TG", "email": "tg@isi.edu"}






    



gc: collecting generation 0...
gc: objects in each generation: 934 1281 64370
gc: done, 588 unreachable, 0 uncollectable, 0.0004s elapsed



In [39]:

    
# Another example
import numpy as np

A = np.array([
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]])
print(A)
AT_A = np.matmul(A.transpose(), A)
print(AT_A)









    



[[1 2 3]
 [4 5 6]
 [7 8 9]]
[[ 66  78  90]
 [ 78  93 108]
 [ 90 108 126]]

About me

BE in CSE at VTU/SJCIT : Class of 2012
MS in CSE at University of Southern California (USC) : Class of 2017

2012 - 2014: Software Engineer @ Simplyphi Software Solutions, Bengaluru
2013 - 2015: Co-Founder @ Datoin.com, Bengaluru
2016 - 2017: Data Scientist @ NASA Jet Propulsion Laboratory, California, USA
2017 - Present: Research Programmer @ USC Information Sciences Institute, California, USA

Committer at Apache Software Foundation
Google Summer of Code 2017 Mentor