Introduction to Python Objects and Strings

Introduction to Python
Programming
Dr.S.Sangeetha
Department of Computer Applications
National Institute of Technology
Tiruchirappalli

Dr.S.Sangeetha, Department of Computer Applications,
NIT Trichy

History
NIT Trichy

Features
Dr.S.Sangeetha, Department of Computer
Applications, NIT Trichy

Working Environment
Anaconda (written in Python)
• Anaconda is a free and open source distribution
• Simplifies package management and deployment
• Package versions are managed by Package Management system Conda
• 1400 + data science packages for Python & R
• IDES – Jupyter, Spyder, Jupyter Lab, R Studio
1. Data Science Libraries in Anaconda
▪ Data Analytics & Scientific Computing – NumPy, SciPy, Pandas , Numba
▪ Visualization
Bokeh, Holoviews, Data shader, Matplotlib
▪ Machine Learning
TensorFlow, H2o, Theano, Scikit learn
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Working Environment Cont…
2. Conda the data science Package & environment Manager
▪ Automatically manage all packages
▪ Work across all platforms (Linux, MacOS, windows)
▪ Create virtual environments
▪ Download Conda Packages from Anaconda, Anaconda enterprise,
conda forge, Anaconda cloud
3. Anaconda Navigator
▪ Desktop Portal

Web framework
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Full Stack
Provide complete support
(Form generations, Template Layouts)
Non – Full Stack
Do not provide additional
functionalities
▪ Django
▪ Web2py
▪ Gitto
▪ Pylon
• Bottle
• Cherrypy
• Flask

Python GUI
▪TKinter – Bundled with Python
▪WXPython
▪PYGUI – Light weight, cross Platform
▪PYside – Nokia
▪PyGObject – bindings for GTK+
▪PyQt5 – bindings for QT application framework
▪Kivy – cross-platform UI creation tool
▪Glade
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Why it is Slow?
1) Dynamically typed Language
2) Interpreted code is always slower
Takes more instructions in order to implement actual machine instruction
3) GIL (Global Interpreter Lock)
➢Allows only one thread to hold the control of python Interpreter
➢Bottleneck in CPU bound multi-threaded code [Even in multi thread architecture
with more than CPU core]
➢Prevents CPU bound threads from executing parallel
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PyPy
1) Uses JIT (Just in Time Compiler)
• JIT (dynamic Translation / run time Compilation)
• Executing computer code that involves compilation during execution of a program
• At run time, prior to execution
• JIT consist of byte code translation to machine code
• JIT compilation combines the speed of compiled code with flexibility of interpretation
• Suited for late bound data types
2) Less memory space
3) Stackless support
• Basic cooperative multitasking.
• Uses ‘tasklets’ to wrap functions
• Creates “micro threads”
• Scheduled to execute concurrently
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Basics of Python
Comments
# Single line or inline comments
1.Data types
Python provides data types such as numeric, complex, strings and Boolean.
It supports no type Declaration.
Numeric
Python has two numeric types int and float
Strings
• ‘Welcome’
• “Welcome”
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Data types cont.….
Multiline strings – Triple quotes
“““Welcome to Python course.
You will learn basics to advanced concepts”””
Boolean
bool is a subtype of int, where True == 1 and False == 0
Complex
>>> complex (10,2)
(10+2j)
>>> x=10+5j
>>> x
(10+5j)
>>> type((10+2j))
<class 'complex'>
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Operators
() {}[] Tuple, List, Dictionary, set display
f (….), x [ :], X.attr Function calls, slicing, Attribute reference
** Exponentiation - Right to left associativity
x, -x Bitwise Not, Negative
*, /, //,% Multiplication, division, floor division,
Modulo division
+ - Additive
<< >> Shift
& Bitwise AND
 Bitwise XOR
| Bitwise OR
in, not in, is, is not <, <=, >, >=, <>, !=, == Membership, Comparison/relational
not Boolean NOT
and Boolean AND
or Boolean OR
lambda Lambda expressions

Quick Demo
Dr.S.Sangeetha, Department of Computer Applications, NIT
Trichy

Objects
• Objects are Python’s abstraction for data.
• Objects are typed
• All data in a Python program is represented by objects or by relations
between objects.
• Every object has an identity, type and value.
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Objects Cont..
Object’s Identity
• Objects have Identity
• Identity is unique and fixed during an object's lifetime
• id() returns an object's identity
• An object’s identity never changes once it has been created
Object Type
• Objects are tagged with their type at runtime
• type determines the operations that the object supports
• type() returns objects type
• Objects contain pointers to their data blob (Binary large object)
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Object categories
▪ Python objects are classified in to categories such as mutable and immutable
• The value of some objects can change.
• Objects whose value can change are mutable
• Objects whose value is unchangeable once they are created are
immutable.
Mutability of the object is determined by its type
• Immutable Object: int, float, complex, string, tuple, bool
• Mutable Object: list, dict, set, byte array, user-defined classes
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Object size
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(100).__sizeof__ ()

Object Structure

Variable
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All variable names are references to the values or objects.

Automatic Garbage Collection
Reference count
sys.getrefcount(100)
del x
del y
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Addons
• Cascading
x=y=z=1+1+1
• Swap
c=4, d=5
c,d = d,c
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Strings
• No character type in Python
• Both ' and “create string literals
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String Slicing
print(X[0:2])
print(X[4:6])
print(X[1:3])
print(X[:3])
print(X[4:])
print(X[1:5:2]) #step size as 3rd parameter
print(X[4::-2])
PY
ON
YT
PYT
ON
YH
OTP
print(X[::-1]) # NOHTYP
Dr.S.Sangeetha, Department of Computer Applications, NIT Trichy

Immutability
>>> x="In India"
>>> id(x)
64787744
>>> x=x+' We have'
>>> x
'In India We have'
>>> id(x)
64763184
>>> y="India"
>>> id(y)
64799392
>>> y[2]="o"
TypeError: 'str'
object does not
support item
assignment
Dr.S.Sangeetha, Department of Computer Applications, NIT
Trichy

String Functions
X = "Welcome to India! "
print(X.lower())
print(X.title())
print(X.upper())
print(X.strip())
print(X.strip('W'))
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welcome to india!
Welcome To India!
WELCOME TO INDIA!
Welcome to India!
elcome to India!

String Functions
X = "Welcome to India!"
print(X.startswith('We'))
print(X.endswith('ia!'))
print(X.isalpha()) # => False (due to '!’)
True
True
False
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String Functions
X = "Welcome to India! "
#search
print('in is found in position',X.find('in’))
#-1 if not found
in is found in position -1
print('In is found in position', X.find('In’))
In is found in position 11
#Replace
print(X.replace('ia', 'onesia'))
Welcome to Indonesia!
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String Formatting
# Curly braces are placeholders
print ('{} is a capital of {}'.format('New Delhi', 'India'))
New Delhi is a capital of India
# position in placeholders
print ("{0} is a capital of {1} in the continent {2}
".format('New Delhi', 'India', 'Asia'))
New Delhi is a capital of India in the continent Asia
# Key of the data items in the placeholders
print("{name} loves {food}". format(name="Reena",
food="Pizza"))
Reena loves Pizza
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String Formatting
# index in the placeholders
Fruits = ['Apple', 'Orange’, 'Guava']
print("{f[0]} is good compared to {f[1]}".format(f=Fruits))
Apple is good compared to Orange
# Evaluated expressions to strings
print ("Square of {} is {}".format (8, 8 ** 2))
Square of 8 is 64
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String Functions
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Other Formatting
print("{:5.2f}".format(3.14159))
3.14
# Reserve spaces and print in middle
print('{:^10}'.format('Centre'))
Centre
# Reserve spaces and print it Left
print('{:<10}'.format('Left'))
Left
# Reserve spaces and print string right
print('{:>10}'.format('Right'))
Right Dr.S.Sangeetha, Department of Computer Applications,
NIT Trichy

Other Formatting
# Padding character
print('{:*^10}'.format('Centre'))
**Centre**
print('{:*<10}'.format('Left'))
Left******
print('{:*>10}'.format('Right'))
*****Right
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Reading Input and Printing output
str=input ("Enter any value")
print (‘output: ', str)
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Writing Simple Program
Demo
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Reference Book
Guido van Rossum and Fred L. Drake Jr, “An Introduction to Python “
Revised and updated for Python 3.2, Network Theory Ltd., 2011.
NIT Trichy

Introduction to Python Objects and Strings

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