My Python Notes: Getting Started

Writing our first Python Program

In order to write python code we need a text editor.
 In this blog i am going to use IDLE(Python), for installing IDLE you can refer my previous post on installing python.

Example 1---Working with print statement
Save the below code as ex1.py
#This is a comment print("###############################") print("I am a statement") """ I am a multiline-comment """ print("----****_____*****-----")

Note: We will execute the code from the windows command prompt.
Save python code in a .py extension
I have saved ex1.py at "E:\python_blog\basics1" location.

now if we open the command prompt by default the location is C: drive

In order to execute our code found at E: driver ,we have to change the location  from C: to E:

In order to execute the python code we first have to navigate to the program location and type "python ex1.py"

Lets us execute another example from python IDLE
Save the below code in ex2.py

Example 2-----Multi-line print statement
print("--------#####----!!!!!") print("Welcome to my blog pythonselenium") #lets write a multi-line statement. print("""I plan to have a series on python and selenium.Selenium is used to test web-applications. """)

Now let execute ex2.py using IDLE
Step 1: Open the file using IDLE

Step 2: Once the file is opened RUN it.

Step 3: Output in the IDLE console

Lessons Learnt

• Comments are meant for readability of a  program a single line comment start with a # symbol and a multi-line comment starts and ends with a """ symbol.
• In order to print statement we use a keyword "print" .
• We can print symbols ,numbers and characters.

-------------*********___________________^^^^^^^^---------!!@@@----------------

Variables

Variables are used to store data ,the data can be numbers,special characters or just plain text.

%s is used for strings and %d is used for numbers.

Save the below code in ex3.py
Example 3 --- working with variables

#This is a comment my_name ="jude augustine job" my_blog ="pythonselenium.blogspot.com" my_age = 24 my_mail ="seleniumusingpython@gmail.com" print("Hi my name is %s"%my_name) print("I am %d years old"%my_age) print("Welcome to my blog %s"%my_blog) print("For any question or clarification you can contact me at %s"%my_mail)

Output

Arithmetic Operators

Operator	Operation	Expression	English description	Result
+	addition	11 + 56	11 plus 56	67
-	subtraction	23 - 52	23 minus 52	-29
*	multiplication	4 * 5	4 multiplied by 5	20
**	exponentiation	2 ** 5	2 to the power of 5	32
/	division	9 / 2	9 divided by 2	4.5
//	integer division	9 // 2	9 divided by 2	4
%	modulo (remainder)	9 % 2	9 mod 2	1

Now when multiple operators are found in  an expression, they are evaluated in the order of precedence.

Operator	Precedence
**	highest
- (negation)
*, /, //, %
+ (addition), - (subtraction)	lowest

Save the below code in ex4.py

Example 4 --- Working with operators

print("An example for arithmetic operators") print(" ") #Find the perimeter of rectangle #variables rectangle_length = 100 rectangle_breadth = 40 perimeter_rectangle = 2*(rectangle_length + rectangle_breadth) print("""The perimeter of rectangle whose length is %d and breadth is %d is found to be %d"""%(rectangle_length,rectangle_breadth,perimeter_rectangle)) print(" ") print("Lets find the sum of two numbers") num1 = 5 num2 = 45 print("""The sum of %d and %d is found to be %d"""%(num1,num2,num1 + num2))

Output

Now in the above example the values ie...variables value are fixed. In order to change the variables values based on the user input we need to accept value from the user.

-------------*********___________________^^^^^^^^---------!!@@@----------------

 Accepting Inputs

Now in the above example the value ie...variables value are fixed. In order to change the variables values based on the user input we need to accept value from the user.
We can receive input from the user using the input() --function

Example 5 --- Working with input() --- function

print("Let us take inputs from the user") print(" ") name = input("Please enter your name: ") location = input("What is your current location: ") print("Hi %s ,how is %s"%(name,location))

Output

Functions

It is block of code that can accomplish a specific task.
Functions usually "take in" data, process it , and "return" a result.
Once a function is written, it can be used over and over again.
Functions can be called from inside of another functions.

Note: When we write a function we are beginning a new block of code, and it starts with a ":" symbol
and the subsequent lines are indented with a tab-space.
In other programming languages we start a new block of code is written within { }.

Function Definition

def function_name(parameters):
      body
      ....
      ....
      ....
   

def--- Keyword used to define a function
function_name---It is the name of the function
parameters--------Function may have parameters
body-------------- 1 or more statements often ending with a return statement

Example 6---Function which take no parameters and no return type
#Function definition def hello_world(): print("I am a function") print("I have no parameters and return type is None") hello_world()

Output

Lets write a function which compute the area of a triangle.

Example 7---Function which take  two parameters and  return type is a number
#compute the area of triangle #Function definition def triangle_area(base,height): area = (1.0/2)*base * height return area #variables triangle_base = 3 triangle_height = 4 #function call area1 = triangle_area(triangle_base,triangle_height) print("""For a triangle whose height is %d and base %d , the area is if found to be %d"""%(triangle_height,triangle_base,area1))

Output

Boolean-Logic

In Boolean-Logic values can be either True or False.
We can perform operation on Boolean-Logic using Boolean-operators.

Boolean-operators---NOT,AND,OR

Truth-table--NOT

a	NOT a
True	False
False	True

Truth-table--AND--OR

a	b	a AND b	a OR b	NOT(a AND b)	NOT(a OR b)
True	True	True	True	False	False
True	False	False	True	True	False
False	True	False	True	True	False
False	False	False	False	True	True

Example 8--Lets write a simple Boolean program 

# Boolean logic and Boolean operators a = True b = False print ("The value of a is %s "%a) print ("The value of b is %s "%b) print ("===") c = not(a) d = a and b print ("Not not a) print (a and b) print (a or b) print (a and b) or (c and (not d))

Output

Comparison Operators

In order to generate Boolean-Logic we use comparison operators.

comparision operators
> greater
< lesser
>= greater and equal to
<= lesser than and equal to
== equal to
!= not equal to

Conditional Statements

We can execute particular statements based on condition.
The condition can be comparison operator or Boolean Logic.

Syntax---if statement

Note :Condition can be formed using comparison operators

if condition:

    statement 1

    ....

    ...

Syntax---if and else

if condition1:

    statement 1

    ....

else:

    statement 2

  

Syntax---if , elif and else

if condition 1:

    statement 1

elif condition 2:

    

    statement 2

else:

    statement 3

Note:We can have 0 or more elif statements.

We can have 0 or 1 else statement and the else statement must be the last statement.

Example 9--Lets write a program using if-elif-else clause.

A train was scheduled to arrive at a particular time and it is now estimated to arrive at another time.

Write a function that returns the train's status: "on time","early" or "delayed".

def train_status(scheduled_time,estimated_time): """ Return the train status (on time,early,delayed) for a train that was scheduled to arrive at the scheduled_time, but is now estimated to arrive at estimated_time. pre-condition: 0.0 <= scheduled_time < 24 and 0.0 <= estimated_time < 24 """ if scheduled_time == estimated_time: return "on time" elif scheduled_time < estimated_time: return "early" else: return "delayed" print("The train is %s "%train_status(9.0,9.0)) print("The train is %s "%train_status(15.0,18.0)) print("The train is %s "%train_status(7.0,4.0))

Output

Function with  Boolean return type

Example -10.1

Write function which tell us if a number is even or not.

Answer:
when  an even number is divide by 2 the remainder is Zero using this we can solve this problem.

def is_even(num): """ Return True if the number is even and false if number is odd. """ if num % 2 == 0: return True else: return False num1 = 5 num2 = 4 print("Is %d even?? %s"%(num1,is_even(num1))) print("Is %d even?? %s"%(num2,is_even(num2)))

The above code can be simplified
Example 10.2

def is_even(num): """ Return True if the number is even and false if number is odd. """ return (num % 2 == 0) num1 = 5 num2 = 4 print("Is %d even?? %s"%(num1,is_even(num1))) print("Is %d even?? %s"%(num2,is_even(num2)))

The output is same for both 10.1 and 10.2

Example 11
Write a function which take two integers, and return the sum of the two integers but if the two number are equal the function return double of the sum of the two integers.

def sum_double(a, b): sum = a + b if a == b: return sum *2 else: return sum print(sum_double(5,5)) print(sum_double(11,12))

Example 12.1
Dog_trouble--We have a dog which barks.Time is represented from 0 to 24.
If the dog is barking and the time is before 7 or after 20,we are in trouble.
Return True if you are in trouble else Falsedef dog_trouble(barking,hour): if barking and ( hour < 7 or hour > 20): return True else: return False print(dog_trouble(True,6)) print(dog_trouble(True,7)) print(dog_trouble(False,21)) print(dog_trouble(True,23)) """Expected output True False False True """

The above example can be simplified
Example 12.2

def dog_trouble(barking,hour): return barking and ( hour < 7 or hour > 20) print(dog_trouble(True,6)) print(dog_trouble(True,7)) print(dog_trouble(False,21)) print(dog_trouble(True,23)) """Expected output True False False True """

Example 13
make10--Write a function given 2 ints, a and b, return True if one if them is 10 or if their sum is 10.

def makes10(a, b): return (a+b==10 or a==10 or b ==10) print(makes10(9,10)) print(makes10(9,9)) print(makes10(12,-2)) """ expected result True False True """