Python : Part 1 - Programming (Python 101)

IDE's used for development : Visual studio code

Extension used in visual studio code :

1. Python
2. Code Runner

Create a simple python file - helloworld.py and run it using the extension Code Runner and will see more details

print('Hello World!')

To see clear output in visual studio code
Go to Visual studio code -> settings ( follow step 1 and step 2)

Step 1: Unselect the checkbox shown in the below image

Step 2 : Clear the previous outputs in visual studio by
Searching Clear Previous Output in settings and select the option

Step 3: Run the code and see the output is clean and clear

Using IDLE :
Go run and search with IDLE and select IDLE App

Run the below commands in IDLE

2+2
print('Hello world!')
name = 'srinivas'
name = + 'ulu'

New window in IDLE, copy the below mentioned code and save it as Hello.py

Hello.py

print('Hello world!')
print('What is your name?') #ask for name
myName=input()
print('Nice to meet you,' + myName)
print('The length of your name is :')
print(len(myName))
print('What is ur age?')
myAge= input()
print('You will be ' + str(int(myAge)+1) + ' in a year.')

Table 1.1 - Comparison Operators

Operator	Meaning
==	Equal to
!=	Not Equal to
<	Less than
>	Greater than
<=	Less than or equal to
>=	Greater than or equal to

Try the below statements in IDLE

42 == 42
42 == 99
2 != 3
2 != 2
'hello' == 'hello'
'hello' == 'Hello'
42 < 100

Table 1.2 - The and Operator’s Truth Table

Expression	Evaluates to
True and True	True
True and False	False
False and True	False
False and False	False

Table 1.3 - The or Operator’s Truth Table

Expression	Evaluates to
True or True	True
True or False	True
False or True	True
False and False	False

Table 1.4 - The not Operator
Unlike and and or, the not operator operates on only one Boolean value (or expression). This makes it a unary operator

Expression	Evaluates to
not True	False
not False	True

1.Flow Control Statements
1.1 if Statements : If the statement clause is true then it will execute else it will skip

if.py

 name = 'Srini'
 if name == 'Srini':
    print('Hi, Srini.')

1.2 else statements: If the statement clause is false then else condition will be executed

else.py

 name = 'Srini'
 if name == 'Srini':
    print('Hi, Srini.')
 else
    print('Hello Stranger')

1.3 elif Statements: You may have a case where you want one of many possible clauses to execute.

elif.py

name = 'Carol'
age = 9999
if name == 'Alice':
    print('Hi, Alice.')
elif age < 12:
    print('You are not Alice, kiddo.')
elif age > 2000:
    print('Unlike you, Alice is not an undead, immortal vampire.')
elif age > 100:
    print('You are not Alice, grannie.')

2. Visualisation: If we wanted to see the visualisation of your program then render the url -https://pythontutor.com/

copy the code in the editor and click on visualise execution

By clicking on Next, we can see the result

3. While loop:

• When the execution reaches the end of a "while" statement's block, it jumps back to the start to re-check the condition.
• You can press ctrl-c to interrupt an infinite loop.
• A "break" statement causes the execution to immediately leave the loop, without re-check the condition.
• A "continue" statement causes the execution to immediate jump back to the start of the loop and re-check the condition.

3.1 Simple while loop program - while1.py

name = ''
while name != 'Srinivas' :
    print('Enter your name:')
    name = input()
print('thank you!')

3.3 While with infinite looping - while_Infinite_Loop.py

while True :
    print('How are you doing buddy')

Note : To break the infinite loop, press Ctrl+C to come out of the loop

3.3 While loop using break - While_break.py

name = ''
while True :
    print('Enter your name:')
    name = input()
    if name == 'srinivas' :
       break
print('Thank you!')

Output:

3.4 While loop with continue - While_Continue.py

count = 0
while count < 5 :
    count = count + 1
    if count == 2 :
        continue
    print(' count is ' + str(count))

Output:

4. for loop :

• "for" loop will loop a specific number of times.
• The range() function can be called with one, two, or three arguments.
• The break and continue statements can be used in for loops just like they're used in while loops.

Using range function in for loop
range(param1,param2,param3)
param1 : start index
param2 : end index
param3 : can be used as increment / decrement the range

4.1 forloop.py

print('My name is')
for i in range(5):
    print('Srinivas Five Times ' + str(i))

Output of the above program :
My name is
Srinivas Five Times 0
Srinivas Five Times 1
Srinivas Five Times 2
Srinivas Five Times 3
Srinivas Five Times 4

4.2 For loop with ranges with single parameter- forloop1.py

total =0
for num in range(101):
   total = total + num
print(total)

Output of the above program :
5050
4.3 For loop with ranges with double parameter- forloop2.py

print('My name is')
for i in range(5,8):
    print('Srinivas Five Times ' + str(i))

Output of the above program :
My name is
Srinivas Five Times 5
Srinivas Five Times 6
Srinivas Five Times 7

4.3 For loop with ranges with triple parameter with incrementing by 1(third parameter) - forloop3.py

print('My name is')
for i in range(0,10,1):
    print('Srinivas Five Times ' + str(i))

Output of the above program :
My name is
Srinivas Five Times 0
Srinivas Five Times 1
Srinivas Five Times 2
Srinivas Five Times 3
Srinivas Five Times 4
Srinivas Five Times 5
Srinivas Five Times 6
Srinivas Five Times 7
Srinivas Five Times 8
Srinivas Five Times 9

4.4 For loop with ranges with triple parameter with decrementing by 1(third parameter) - forloop4.py

print('My name is')
for i in range(5,-1,-1):
    print('Srinivas Five Times ' + str(i))

Output of the above program :
My name is
Srinivas Five Times 5
Srinivas Five Times 4
Srinivas Five Times 3
Srinivas Five Times 2
Srinivas Five Times 1
Srinivas Five Times 0

5.Python Builtin Functions:

5.1 Built in functions:

• print()
• len()
• input()

5.1.1 Import the modules

5.2.1 Import single library

import random
random.randint(1,10)

Note: Try the above command in IDLE shell, we will keep getting random numbers.

5.1.2 Import multiple libraries

import random,sys,os,math
from random import *   # this is alternative to import statement
randint(1,10)

Note : No need to call random.randint(1,10) in the above scenario

5.1.3 sys.exit()

import sys
print('Hello')
sys.exit()
print('Good bye')

Output is
Hello

5.1.4 Third party modules : We can install the third party modules using pip program and which also comes with python

• The pyperclip third-party module has copy() and paste() functions for reading and writing text to the clipboard. Reference :https://automatetheboringstuff.com/appendixa/ Go go ahead and install The pyperclip Module

import pyperclip
pyperclip.copy('Hello World!')
pyperclip.paste()

Output of the above program is
Hello World!

5.2.Write your own functions:

Example 1 : function1.py

def hello() :
    print('Ireland')
    print('UK')
    print('Chennai')

hello()
hello()
hello()

Output of the above program is
Ireland
UK
Chennai
Ireland
UK
Chennai
Ireland
UK
Chennai

Note : Copy the above code and try in https://pythontutor.com/

5.2.1 Try to add arguments to the functions

def hello(name) :
    print('Hello ' +name)

hello('Srini')
hello('Bob')

5.2.2 Return from function

Try the below items in IDLE shell
print('Hello')
print('World')

print('Hello', end='')
print('world')
print('cat','dog','mouse')
cat dog mouse

print('cat','dog','mouse',sep='$$')
cat$$dog$$mouse

6.Global and local scope variables

• The global scope is code outside of all functions. Variables assigned here are global variables.
• Each function's code is in its own local scope. Variables assigned here are local variables.
• Code in the global scope cannot use any local variables.
• If there's an assignment statement for a variable in a function, that is a local variable. The exception is if there's a global statement for that variable; then it's a global variable.

6.1 Example 1

spam =42 # global variable

def sum():
    spam = 42 # local variables
print('Some code here')
print('Some code here')

6.2 Example 2

def spam():
    egg = 99
    bacon()
    print(eggs)

def bacon():
    ham = 101
    eggs = 0

spam()

6.3 Example 3

def spam():
    global eggs  # to use the variable as global 
    eggs = 'Hello'
    print(eggs)

eggs =42
spam()
print(eggs)

7.Exception Handling:

7.1 Example1 : exception.py

def div64by(divideBy):
    return 64  / divideBy

print(div64by(2))
print(div64by(8))
print(div64by(0))
print(div64by(1))

Code fails in printing the function 3 with division by 0 error

• Exceptions can be handled using try and except statements

7.1.1 Modify the above code

def div64by(divideBy):
    try:
        return 64  / divideBy
    except ZeroDivisionError :
        print('Error:You tired to divide by zero.')

print(div64by(2))
print(div64by(8))
print(div64by(0))
print(div64by(1))

Output of the above program is

32.0
4.0
Error:You tired to divide by Zero
None
64.0

7.2 Example 2

• Try the birds count as integer and check the output
• Then try with string as input, it will fail then handle it using try and except

print('How many birds do you have?')
numbirds = input()
if int(numbirds) >= 4 :
       print('That is a lot of birds')
 else:
        print('That is not that many birds')

print('How many birds do you have?')
numbirds = input()
try:
    if int(numbirds) >= 4 :
       print('That is a lot of birds')
    else:
        print('That is not that many birds')
except ValueError:
    print ('You did not enter a number.')

• A divide-by-zero error happens when Python divides a number by zero.
• Errors cause the program to crash.
• An error that happens inside a try block will cause code in the except block to execute. That code can handle the error or display a message to the user so that the program can keep going.

8. Lists: (using IDLE shell for below demos)

8.1 Simple List

#1. Try the commands in the IDLE Shell
['cat','bat','rat','elephant']

#2. Commands in IDLE Shell
info = ['cat','bat','rat','elephant']
info

# To Access values in a list, use indexes
#3. Try the commands in IDLE Shell
info[0]
info[1]
info[2]

8.2 Lists of Lists

spam = [ ['cat','bat'],[10,20,30,40]]

spam[0]
['cat','bat']

spam[1]
[10,20,30,40]

spam[0][0]
spam[0][1]
spam[1][0]
spam[1][1]
spam[1][2]

# Try all the above commands in python visualise

8.3 Negative Indexes

• -1 => Refers to last Index
• -2 => Refers to last but one Index

info = ['cat','bat','rat','elephant']
info[-1]
'elephant'
info[-2]
'rat'

8.4 Try with string concatenation with lists

'The' + info[-1] + ' is afraid of the ' + info[-3] +'.'
Output is
'The elephant is afraid of the bat.'

Index is single Value
Slice is list of values

info[1:3]
['bat','rat']

8.5 Changing a List's item

info = 'Hi Dude !'
info # 'Hi Dude !'
info =[10,20,30]
info[1] =['Cat','Dog','Mouse']
info # [10,'Cat','Dog','Mouse']

8.6 Slice Shortcuts

info=['cat','bat','rat','elephant']
info[:2] # When the start index is empty , it will treat as 0
# output is ['cat','bat']

info[1:] # When the end index is empty, it count till the end

8.7 Delete a item from a list using del statements

del statement is a unassigned statement

del info[2]

info
# output is ['cat','bat','elephant']


del info[2]

info
# output is ['cat','bat']

8.8 String and list similarities

len('Hello')
# output - 5
len([1,2,3])
# output  - 3
'Hello ' +'world'
# output - Hello world
[1,2,3] + [4,5,6]
#output - [1,2,3,4,5,6]

# string replication
'Hello'*3 
#list replication
[1,2,3] * 3   # ouput : [1,2,3,1,2,3,1,2,3]

list('hello')  # ['H','e','l','l','o']

# in and out operators

'howdy' in [ 'hello','hi','howdy','heyas'] # output - True

'howdy' not in [ 'hello','hi','howdy','heyas'] # output - False

8.9 For loops with lists:

#1
for i in range(4):
    print(i)

#2
range(4)
range(0,4)
#output- [0,1,2,3]

#3
for i in [0,1,2,3]:
    print(i)
#ouput
0
1
2
3

#4
list(range(4))
# output : [0,1,2,3]

#5
list(range(0,10,2))
# output :  [0,2,4,6,8,10]

# for i in range(len(somelist)) :

#6
supplies = ['pens','staplers','pins','books']
for i in range(len(supplies)):
    print('Index ' +str(i) +' in supplies is:  ' + supplies[i])

Index 0 in supplies is pens 
Index 1 in supplies is staplers 
Index 2 in supplies is pins 
Index 3 in supplies is books 

8.10. Multiple Assignments in lists:

#1
info = ['fat','orange','loud']
size = info[0]
color = info[1]
di = info[2]

Muliple variable assignments

size,color,di = cat 
#0 index maps to first variables, 1 index maps to second variables and etc.,
size # 'fat'
di # 'loud'

*# n to n variables assignment *

size,color,di = 'skinny','blue','noisy'

a= 'AAA'
b='BBB'
#if you wanted to swap variables
a,b= b,a

8.11 Augmented operators

Augmented Assignment Statement	Equivalent Statement
info+=1	info =info+1
info-=1	info =info-1
info*=1	info =info*1
info/=1	info =info/1
info%=1	info =info%1

8.12 List Methods

• index()
• append()
• insert()
• remove()
• sort()

8.12.1. index()

spam = ['hello','hi','howdy','heyas']
spam.index('hello')
#output : 0

spam.index('howdy')
#output : 2

#if the list is having duplicate values
spam = ['hello','hi','howdy','howdy']
spam.index('howdy')
#ouput : 2 # it will return the first index

*8.12.2. append(),insert(),remove(),sort() *

#append() method
spam = ['cat','dog','bat']
spam.append('rat')
['cat','dog','bat','rat']


#insert() method
spam = ['cat','dog','bat']
spam.insert(1,'rat')
['cat','rat','dog','bat']


#Try with strings
info= 'hello'
info.append(' world')

#remove() method

info = ['cat','dog','bat']
info.remove('bat')
info
['cat','dog']


#delete using del
del info[0]
info
['dog']

# if the list having duplicate values
info = ['cat','dog','bat','cat','dog','bat']
info.remove('cat')
info

#output :
['dog','bat','cat','dog','bat']

#sort() method

#1
spam = [1,2,3.14.5,-7]
spam.sort()
spam
#ouput - [-7,1,2,3.14,5]

#2
spam = ['ants','badgers','cat','dogs']
spam.sort()
spam

#3
spam.sort(reverse=True)
spam

#4
spam = [2,3,4,'dogs','cats']
spam.sort()

#output : It will fail - unordertable types - str and int


#5
spam = ['Alice','Bob','apple','carol']
spam.sort()

References :
www.python.org
https://pythontutor.com/
https://docs.python.org/3/tutorial/

Conclusion : Discussed about basics of python with samples and dicussed visual studio code edito and extension in visual studio and IDLE shell command for running the python code

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