python programming

1. 17CSC02-PYTHON
PROGRAMMING
Introduction to Python
UNIT - II

2. LEARNING OUTCOME
A student who successfully completes
the course will have the ability to:
Understand the basics of python
programming constructs.
2

3. UNIT – 1I
Introduction to Python
History-features-execution of python
program-flavors of python-comments-
data types-built in data types-
sequences-literals-operators-input and
output statements-conditional
statements-if-if-else-nested if else-for-
while-nested loops-break-continue-
pass-assert-return.
3

4. Computer Program
 A computer program is a collection of
instructions that performs a specific
task when executed by a computer.
 A computer requires programs to
function and typically executes
the program's instructions in a central
processing unit.
4

5. CHARACTERISTICS OF
COMPUTER PROGRAM
 Efficient-execute faster, utilize minimal
memory
 Good User Interface-friendly user
interface
 Reliable-handle unexpected errors,
give proper messages if error occur.
 Good communication-self explanatory
 Portable-platform independent, run on
variety of systems.
5

6. Programming Errors
 Syntax error- structure of the program
 Semantic error-meaning of the
syntactical structure.
 Runtime error-program executed
6

7. Natural Language Vs Formal
Language
 NL:
 - spoken by people
 Closer to humans
 Ambiguous in nature, more redundant
 Eg: french , english, german
 FL:
 -for specific applications
 -closer to computer code.
 -unambiguous in nature
 -less redundant
 Eg: all programming
7

8. Programming paradigms
 Two type:
 Procedural programming
 Object oriented programming
8

9. Procedural programming
 Data and operations on data are
seperated.
 Does not support the concept of data
hiding and encapsulation.
 Follows top down approach
 Global data sharing is allowed.
 Eg: c, pascal.
9

10. Object oriented programming
 Bottom up approach
 Supports data hiding and encapsulation.
 Data can be easily move between
methods and can be controlled through
access specifiers.
 Eg: java, c++.
Python is a procedure oriented
programming as well as object oriented
programming.
10

11.  Python is a typeless programming
language.
 Typeless-value of the variable
determines the type.
 Type checking is made at run time.
 Need not worry about the type of the
variable.
 Eg: python, perl, PHP.
11

12. PYTHON OVERVIEW
 Python is a high-level, interpreted,
interactive and object-oriented scripting
language. Python is designed to be
highly readable. It uses English
keywords frequently where as other
languages use punctuation, and it has
fewer syntactical constructions than
other languages.
 Python is Interpreted:
 Python is Interactive:
 Python is Object-Oriented:
 Python is a Beginner's Language:
12

13.  Python is Interpreted: Python is processed at
runtime by the interpreter. You do not need to
compile your program before executing it. This is
similar to PERL and PHP.
 Python is Interactive: You can actually sit at a
Python prompt and interact with the interpreter
directly to write your programs.
 Python is Object-Oriented: Python supports
Object-Oriented style or technique of
programming that encapsulates code within
objects.
 Python is a Beginner's Language: Python is a
great language for the beginner-level
programmers and supports the development of a
wide range of applications from simple text
processing to WWW browsers to games
13

14. History of Python
 Conceived in the late 1980’s.
 Developed in the year 1989 by Guido
van Rossum who was working for
centrum wiskunde & informatica(CWI) at
netherlands.
 as a successor to the ABC (programming
language) capable of exception
handling and interfacing with
the Amoeba operating system
 He published the first version of the
python(0.9.0) on February 1991.
14

15.  Python is derived from many other
languages, including ABC, Modula-3,
C, C++, Algol-68, SmallTalk, and Unix
shell and other scripting languages.
 Python is copyrighted. Like Perl,
Python source code is now available
under the GNU General Public
License (GPL).
15

16. VERSIONS OF PYTHON
 Release dates for the major and minor versions:[29]
 Python 1.0 - January 1994
◦ Python 1.5 - December 31, 1997
◦ Python 1.6 - September 5, 2000
 Python 2.0 - October 16, 2000
◦ Python 2.1 - April 17, 2001
◦ Python 2.2 - December 21, 2001
◦ Python 2.3 - July 29, 2003
◦ Python 2.4 - November 30, 2004
◦ Python 2.5 - September 19, 2006
◦ Python 2.6 - October 1, 2008
◦ Python 2.7 - July 3, 2010
 Python 3.0 - December 3, 2008
◦ Python 3.1 - June 27, 2009
◦ Python 3.2 - February 20, 2011
◦ Python 3.3 - September 29, 2012
◦ Python 3.4 - March 16, 2014
◦ Python 3.5 - September 13, 2015
◦ Python 3.6 - December 23, 2016
16

17. FEATURES OF PYTHON
 Easy-to-learn: Python has few keywords,
simple structure, and a clearly defined
syntax. This allows the student to pick up the
language quickly.
 Easy-to-read: Python code is more clearly
defined and visible to the eyes.
 Easy-to-maintain: Python's source code is
fairly easy-to-maintain.
 A broad standard library: Python's bulk of
the library is very portable and cross-platform
compatible on UNIX, Windows, and
Macintosh.
 Interactive Mode:Python has support for an
interactive mode which allows interactive
testing and debugging of snippets of code. 17

18.  Portable: Python can run on a wide variety of hardware
platforms and has the same interface on all platforms.
 Extendable: You can add low-level modules to the
Python interpreter. These modules enable programmers
to add to or customize their tools to be more efficient.
 Databases: Python provides interfaces to all major
commercial databases.
 GUI Programming: Python supports GUI applications
that can be created and ported to many system calls,
libraries and windows systems, such as Windows MFC,
Macintosh, and the X Window system of Unix.
 Scalable: Python provides a better structure and
support for large programs than shell scripting.
18

19.  Python has a big list of good features, few
are listed below:
 It supports functional and structured
programming methods as well as OOP.
 It can be used as a scripting language or can
be compiled to byte-code for building large
applications.
 It provides very high-level dynamic data types
and supports dynamic type checking.
 IT supports automatic garbage collection.
 It can be easily integrated with C, C++, COM,
ActiveX, CORBA, and Java.
19

20. EXECUTION OF PYTHON
 Python source code is compiled to a byte
code.
 The file has a .pyc extension.
 Program.py is compiled into
program.pyc.
 The byte code file is then inputted to the
PVM which interprets the byte code and
produces the desired output.
 The generation of byte code file and its
execution by the PVM is done
automatically in python and user need
not worry about it. 20

21.  If the python has write access on
computer, it stores the byte code in
computer (.pyc extension).
 Python saves byte code as its help in
start up speed optimization.
 The next time if we run the program
python will load the .pyc file and skip
compilation step.
 As long as we need not changed
source code since the byte code was
saved.
21

22.  If python does not have write access
on computer it generates the byte
code and stores it in memory which is
ultimately discard when the program
exits.
22

23. 23
Program.py
Program.pyc
PVM
Python output

24. What is python?
 Python is a programming language
that combines the features of C and
java.
 Offers elegant style of developing
programs like C.
 When the programmers want to go for
object orientation, python offers
classes and objects like java.
24

25. Example-add two numbers
 a=b=10
 Print(“sum=“,(a+b)
 Python name-from TV show “monty
python’s flying circus”.
 Logo:
25

26.  Python is open source software, which
means anybody can download it from
www.python.org and use it to develop
programs.
26

27. Flavors of python
 Flavors-Different types of python
compilers.
 Used to include various programming
languages into python.
 CPython
 Jython
 IronPython
 PyPy
 RubyPython
 StacklessPython
 Pythonnxy
 AnacondaPython
27

28. Cpython:
 Standard python implemented in C.
 www.python.org/downloads/.
 In this any python program is internally
converted into byte code using C
language functions.
 Byte code is run on the interpreter
available in python Virtual Machine
(PVM)created in C.
 Possible to execute C and C++
functions and programs.
28

29. Jyhton:
 Known as JPython.
 Designed to run on java platform.
 In this compiler first compiles the
python program into java byte code.
 Byte code is executed by java virtual
machine(JVM).
 Libraries are useful for both python
and java programmers.
 www.jython.org
29

30. IronPython:
 Used for .NET Framework.
 Written in C# language.
 When compiled gives an IL which runs
on CLR to produce output.
 This flavor gives flexibility of using
both .NET and python libraries.
 www.ironpython.net/.
30

31. PyPy:
 Python implementation using python
language.
 Written in Rpython which was created
in python language.
 Rpyhton is useful for creating
language interpreters.
 PyPy programs run very faster since
there is a JIT(Just in Time) compiler
added with PVM.
 Pypy.org/download.html.
31

32. RubyPython
 Bridge between the Ruby and Python.
 Encloses python interpreter inside
ruby applications.
 Rubypythons.org/gems/rubypython/ve
rsions/0.6.3.
32

33. StacklessPython:
 Small tasks which should run
individually are called tasklets.
 Tasklets run independently on CPU
and can communicate via channels.
 A Channal is a manager that takes
care of scheduling the tasklets,
controlling them and suspending
them.
 A thread is a process which runs
hundreds of such tasklets. 33

34.  Create thread and tasklets in
stacklesspython which is
reimplementation of original python.
 Pypi.python.org/pypi/stack-less-
python/10.0
34

35. Pythonxy:
 Pronouned as python xy and written
as python(X,Y).
 Used for scientific and engineering
related packages.
 Python-xy.github.ioo/downloads.html
35

36. Anaconda python:
 Handling large scale data processing,
predictive analytics and scientific
computing- called anaconda python.
 Focus on large scale of data.
 www.continuum.io/downloads.
36

37. PVM
 Convert any program into machine
code before it is submitted to the
computer for execution
 Compiler normally converts program
source code to machine code.
 In python program code is converted
into byte code
37

38. PVM-what is byte code?
 Byte code represents the fixed set of
instructions created by python
developers representing all types of
operations.
 The size of each byte instruction is 1
byte.
 Python organization says that there
may be newer instructions added to
the existing byte code from time to
time.
38

39. Role of PVM:
 Convert the byte code instructions into
machine code .
 PVM is equipped with an interpreter.
 Interpreter converts the byte code to
machine code.
 So PVM is called as interpreter.
39

40. C and PYTHON
C Python
Procedure oriented language. Does not contain the features
like classes , object etc
Procedure oriented language. Does contain the features like
classes , object etc
Executes faster. Slower compared to C
Need to declare data types of variables, arrays Type declaration is not required
Type discipline is static and weak. Strong and dynamic
Pointers used in C Does not use pointers
No exception handling facility Handles exceptions.
C has while, do.. while, for loop Python has while and for loop.
Switch statement Does not have switch
The variable in the for loop does not incremented
automatically
The variable in the for loop incremented automatically
40

41. C and PYTHON
c Python
Allocate and deallocate memory using malloc(), calloc()
functions
Allocate and deallocate memory using PVM automatically
Does not contain garbage collector Automatic garbage collector is available.
Semicolon is used to terminate the statements No need semicolon.
41

42.  Argparse –command line parsing lib
 Boto- amazon web services
 Cherrypy-object oriented http framework
 Cryptography
 Fiona-big data file
 Jellyfish-strings
 Mysql-connector python-daatbase
 Numpy-single and multi array
 Pandas-daat structures
 Pillow-image
 Pyquery-lib in python
 Scipy-scientific and engineering
 Sphinx-documentation generator
 Sumpy-algebra
 W3lib-web based
 Whoosh-indexing and searching
42

43.  C:>python –m dis program.py
43

44. How python sees variable?
 In programming languages:
 Variable is connected to memory
location.
 Storage box or container- store the
value.
 Eg:
 a=1;

 a
 Some memory is allocated with the 44
1

45.  If we change the value of the variable ,
then the box will be updated with the
new value.
 a=2;
 a
 Int b=a;
 A new memory box is created by the
name ‘b’ and value of a is copied to ‘b’.

 b a
45

46.  In python:
 Variable is seen as a tag(name)that is
tied to some value.
 a=1
 Value ‘1’ is created first in memory and
then a tag is created
 a 1
 Values as objects.
46

47.  If we change the value of ‘a’ to a new
values as a=2,
 Then the tag is simply changed to the
new value.
 The value ‘1’ is unreferenced object.
Removed by garbage collector.
 a 2 1
 If b=a,
 a
 b 2
47

48.  Python has tags to represent the
values.
 Only one memory referenced by two
names.
 Python is using memory efficiently.
48

49. Comments
 Comments can be used to make the code more readable.
 Comments can be used to prevent execution when testing
code.
 Two types:
◦ Single line #
◦ Multi line comments “”” “””
 Single line comments: #
 Eg: #print("Hello, World!")
print("Cheers, Mate!") # hello world
a=10 # 10 is assigned to a
• Multi line comments(block comments): used to comment
multiple lines.
It uses triple double quotes(“””) or triple single quotes(‘’’)
• Eg:
"""
This is a comment
written in
more than just one line
"""
print("Hello, World!")
49

50. Opening Python Shell Prompt
 Let’s begin by opening Python’s GUI by
pressing “Start” and typing “Python” and
selecting the “IDLE (Python GUI).”
50

51. Python Running Modes
 Interpreter mode or Conversation mode called IDLE
 Script mode (“Filename.py”)
◦ Extension of python script is .py
◦ Press F5 key to run the script.
51

52. IDLE Development Environment
 IDLE is an Integrated Development Environment
for Python, typically used on Windows
 Multi-window text editor with syntax highlighting,
auto-completion, smart indent and other.
 Python shell with syntax highlighting.
 Integrated debugger with stepping and persistent
breakpoints
52

53. The Python Interpreter
Hello World
•Python is an interpreted language
•The interpreter provides an interactive environment to play with the language
•Results of expressions are printed on the screen
53
>>> “hello world”
hello world
>>> print “Hello world”
Hello world
>>> 3 + 7
10
>>> 3 < 15
True
>>> print “print me”
print me

54. The print Statement
• Elements separated by commas print with a space between them
• A comma at the end of the statement (print ‘hello’,) will not print a newline character
• can use single quotes ( ‘’ )
• can use double quotes ( “”)
• can use triple quotes (“”” “”””)
54
>>> print 'hello'
hello
>>> print 'hello', 'there'
hello there
>>> print “hello world”
Hello world
>>> print “””Hello World”””
Hello World

55. Data types
 Type of data stored into a variable or
memory.
 1.Built-in data types
 2.User defined data types
55

56. Built in data types:
Five types:
 None type
 Numeric types
 Sequences
 Sets
 Mappings
56

57. None type:
 An object that does not contain any
value.
 Java- ‘null’ objects.
 Python-’none’ object
 Maximum of only one ‘none’ object is
provided.
 It is used inside a function as a default
value of the arguments.
 When calling the function , if no value is
passed, then the default value is ‘none’.
 Boolean expressions-’none’ –false.
57

58. Numeric types:
Represent numbers. Three sub types;
1. int
2. float
3. Complex
58

59. Int type
 Represents an integer.
 Integere- wothout any decimal point.
 Eg: 122,0,-31225
 No limit for the size of an int datatype.
Examples
x = 20
#display x:
print(x)
#display the data type of x:
print(type(x))
Output
20
<class 'int'>
59

60. Int type continuee
x = int(20)
#display x:
print(x)
Output
60

61. Float type:
 Represents floating point number.
 Contain decimal number
 Eg: -3.2,0.12,782.23 etc.,
 Num=3.12
 Floating point number can also be written in scientific
notation ‘e’ or ‘E’ to represent the power of 10.
 Eg: 2.5 X 104 -2,5E4
 Example
x = float(20.5)
#display x:
print(x)
Output:
61

62. Complex type:
 Complex number is written in the form of
a+bj or a+bJ
 Here ‘a’ represents the real part
 Here ‘b’ represents the imaginary part.
 Eg: 3+5j, 3+5J
Example
x = complex(1j)
#display x:
print(x)
Output
lj
62

63. Representing binary, Octal and
Hexadecimal numbers
 Binary number- 0b or 0B before the
value.
 Eg:0b11011
 Hexadecimal value:- 0x or 0X
 Octal number-0o or 0O
63

64. Converting data types
 Depending on the type of data , python
internally assume the type of variable.
 The programmer wants to convert one
data type into another data type- type
conversion or coercion.
 Possible by mentioning with parenthesis.
 Eg: int(num).
 Program(ty.txt)
 Convert.txt
64

65.  There is a function in the form of
int(str, base)- contvert string
into a decimal integer.
It should contain integer number in
string format.
‘base’- base of the number system.
Eg: base 2 represents binary number
16 indicates hexadecimal number.
Program-convert1.txt
65

66.  Bin() convert the number into binary
form
 oct() convert the number into octal
form
 hex() convert the number into
hexadecimal form.
66

67. Bool type
 Represent boolean values.
 Two values ‘true’ or ‘false’
 True=1, false=0
 A blank string “” is also represented as
false.
 Eg:
 a=10, b=20
 If(a<b):print(“hello”)
67

68.  a=10>4
 print(a)- displays true
a=4>10
Print(a)- display false
68

69. Sequences in python
 Group of elements or items.
 Eg: group of integer will form a
sequence.
 Six types
 1. str
 2. bytes
 3.bytearray
 4.list
 5.tuple
 6.range
69

70. Str data type
 Represents string data type.
 A string is represented by a group of
characters.
 String are enclosed with single or double
quotes.
 Both are valid.
Eg:
Str=“welcome”
Str=‘welcome’
Use “”” or’’’ quotes for representing a
group of lines including spaces.
70