Python4HPC.pptx

Introduction to Python
Priyanka
Welcome Python Programming
1

Python!
• Created in 1991 by Guido van Rossum (now at Google)
– Named for Monty Python
• Useful as a scripting language
– script: A small program meant for one-time use
– Targeted towards small to medium sized projects
• Used by:
– Google, Yahoo!, Youtube
– Many Linux distributions
– Games and apps (e.g. Eve Online)

Interpreted Languages
• Interpreted
– Not compiled like Java
– Code is written and then directly executed by an interpreter
– Type commands into interpreter and see immediate results
Computer
Runtime
Environment
Compiler
Code
Java:
Computer
Interpreter
Code
Python:

Installing
Python
• Windows:
• Download Python from
http://www.python.or
g
• Install Python.
• Run Idle from the Start
Menu.

The Python Interpreter
• Allows you to type commands one-at-a-time and see results
• A great way to explore Python's syntax
– Repeat previous command: Alt+P

How to run Python Windows
• Run IDLE to use the interpret
• Open a new window in IDLE to write and save programs

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Filename, preferred extension is py
User Program

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•Standard Python IDE (Integrated Development
Environment)
•Main components: Editor, Shell, and Debugger
•Editor: Write and edit Python scripts
•Shell: Execute Python commands interactively
•Debugger: Helps in finding and fixing errors in
code

Python Shell is Interactive
Feb-24 Programming
12
IN[1]:
IN[2]:
IN[4]:
IN[3]:
Python Shell Prompt
User Commands
(Statements)
Outputs
( )

Interacting with Python Programs
• Python program communicates its results to
user using print
• Most useful programs require information
from users
– Name and age for a travel reservation system
• Python 3 uses input to read user input as a
string (str)
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input
• Take as argument a string to print as a prompt
• Returns the user typed value as a string
– details of how to process user string later
Feb-24 Programming 14
IN[1]:
IN[2]:
IN[3]:
( )

Types in Python
• int
– Bounded integers, e.g. 732 or -5
• float
– Real numbers, e.g. 3.14 or 2.0
• long
– Long integers with unlimited precision
• str
– Strings, e.g. ‘hello’ or ‘C’
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Operators
• Arithmetic
• Comparison
• Assignment
• Logical
• Bitwise
• Membership
• Identity
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+ - * // / % **
== != > < >= <=
= += -= *= //= /= %= **=
and or not
in not in
is is not
& | ^ ~ >> <<

Programming using Python
Operators and Expressions
2/1/2024
18
Programming

Binary Operations
2/1/2024 Programming
19
Op Meaning Example Remarks
+ Addition 9+2 is 11
9.1+2.0 is 11.1
- Subtraction 9-2 is 7
9.1-2.0 is 7.1
* Multiplication 9*2 is 18
9.1*2.0 is 18.2
/ Division 9/2 is 4.25 In Python3
9.1/2.0 is 4.55 Real div.
// Integer Division 9//2 is 4
% Remainder 9%2 is 1

Conditional Statements
• In daily routine
–If it is very hot, I will skip
exercise.
–If there is a quiz tomorrow, I will
first study and then sleep.
Otherwise I will sleep now.
–If I have to buy coffee, I will
go left. Else I will go
straight.
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if-else statement
• Compare two integers and print the min.
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21
1. Check if x is less
than y.
2. If so, print x
3. Otherwise, print y.
if x < y:
print (x)
else:
print (y)
print (‘is the minimum’)

if statement (no else!)
• General form of the if statement
• Execution of if statement
– First the expression is evaluated.
– If it evaluates to a true value, then S1 is
executed and then control moves to the S2.
– If expression evaluates to false, then control
moves to the S2 directly.
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if boolean-expr :
S1
S2
S1
S2

if-else statement
• General form of the if-else statement
• Execution of if-else statement
– First the expression is evaluated.
– If it evaluates to a true value, then S1 is executed and
then control moves to S3.
– If expression evaluates to false, then S2 is executed
and then control moves to S3.
– S1/S2 can be blocks of statements!
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if boolean-expr :
S1
else:
S2
S3
S2
S1
S3

Nested if, if-else
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if a <= b:
if a <= c:
…
else:
…
else:
if b <= c) :
…
else:
…

Elif
• A special kind of nesting is the chain of if-
else-if-else-… statements
• Can be written elegantly using if-elif-..-else
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if cond1:
s1
elif cond2:
s2
elif cond3:
s3
elif …
else
last-block-of-stmt
if cond1:
s1
else:
if cond2:
s2
else:
if cond3:
s3
else:
…

Programming using Python
Loops
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Python Programming

Printing Multiplication Table
5 X 1 = 5
5 X 2 = 10
5 X 3 = 15
5 X 4 = 20
5 X 5 = 25
5 X 6 = 30
5 X 7 = 35
5 X 8 = 40
5 X 9 = 45
5 X 10 = 50
Feb-24 Python Programming
27

Program…
28
n = int(input('Enter a number: '))
print (n, 'X', 1, '=', n*1)
print (n, 'X', 2, '=', n*2)
print (n, 'X', 3, '=', n*3)
print (n, 'X', 4, '=', n*4)
print (n, 'X', 5, '=', n*5)
print (n, 'X', 6, '=', n*6)
….
Too much
repetition!
Can I avoid
it?

Print n X i = n*i
i = i+1
Input n
i = 1
i <=10
TRUE FALSE
29
Stop
Loop
Loop Entry
Loop Exit

30
n = int(input('n=? '))
i = 1
while (i <= 10) :
print (n ,'X', i, '=', n*i)
i = i + 1
print ('done‘)
Print n x i = ni
i = i+1
Input n
i = 1
TRUE
i <=10
FALSE
Stop

While Statement
1. Evaluate expression
2. If TRUE then
a) execute statement1
b) goto step 1.
3. If FALSE then execute statement2.
31
while (expression):
S1
S2
FALSE
TRUE
S1
expression
S2

For Loop
32
• Print the hi for 100 times.
# the for loop
for i in range(1,101):
print(“hi”)

For loop in Python
• General form
33
for variable in sequence:
stmt

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