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condition & iteration
  practice  
  assignment  
  solution  

Condition

Conditionals - mostly in the form of if statements - are one of the essential features of a programming language and Python is no exception. You will find hardly any programming language without an if statement.1 There is hardly a way to program without having branches in the flow of code. At least, if the code has to solve some useful problem. 

A decision has to be taken when the script or program comes to a point where it has a choice of actions, i.e. different computations, to choose from. 
The decision depends in most cases on the value of variables or arithmetic expressions. These expressions are evaluated to the Boolean values True or False. The statements for the decision taking are called conditional statements. Alternatively they are also known as conditional expressions or conditional constructs. 
If it rains tomorrow, I will tidy up the cellar. After this I will paint the walls. If there is some time left, I will do my tax declaration. Otherwise, I will go swimming. In the evening, I will go to the cinema with my wife!

 

 

The following Python script implements this "dog years algorithm":
age = int(input("Age of the dog: "))
print()
if age < 1:
print("This can hardly be true!")
elif age == 1:
print("about 14 human years")
elif age == 2:
print("about 22 human years")
elif age > 2:
human = 22 + (age -2)*5
print("Human years: ", human)
input('press Return>')
 
We will read in three float numbers in the following program and will print out the largest value: 
x = float(input("1st Number: "))
y = float(input("2nd Number: "))
z = float(input("3rd Number: "))
if x > y and x > z:
maximum = x
elif y > x and y > z:
maximum = y
else:
maximum = z
print("The maximal value is: " + str(maximum))

 

 

iteration

In general, statements are executed sequentially: The first statement in a function is executed first, followed by the second, and so on. There may be a situation when you need to execute a block of code several number of times.
Programming languages provide various control structures that allow for more complicated execution paths.
A loop statement allows us to execute a statement or group of statements multiple times.

Python programming language provides following types of loops to handle looping requirements.

Loop Type

Description

for loop

Executes a sequence of statements multiple times and abbreviates the code that manages the loop variable.

while loop

Repeats a statement or group of statements while a given condition is TRUE. It tests the condition before executing the loop body.

nested loops

You can use one or more loop inside any another while, for or do..while loop.


 

for loop

for letter in 'Python': # First Example
print 'Current Letter :', letter
fruits = ['banana', 'apple', 'mango']
for fruit in fruits: # Second Example
print 'Current fruit :', fruit
fruits = ['banana', 'apple', 'mango']
for index in range(len(fruits)):
print 'Current fruit :', fruits[index]
Current fruit : banana
Current fruit : apple
Current fruit : mango

 

 

for num in range(10,20): #to iterate between 10 to 20
for i in range(2,num): #to iterate on the factors of the number
if num%i == 0: #to determine the first factor
j=num/i #to calculate the second factor
print '%d equals %d * %d' % (num,i,j)
break #to move to the next number, the #first FOR
else: # else part of the loop
print num, 'is a prime number'
10 equals 2 * 5
11 is a prime number
12 equals 2 * 6
13 is a prime number
14 equals 2 * 7
15 equals 3 * 5
16 equals 2 * 8
17 is a prime number
18 equals 2 * 9
19 is a prime number

 

 

while loop

count = 0
while (count < 9):
print 'The count is:', count
count = count + 1


Infinite Loop

var = 1
while var == 1 : # This constructs an infinite loop
num = raw_input("Enter a number :")
print "You entered: ", num
 
count = 0
while count < 5:
print count, " is less than 5"
count = count + 1
else:
print count, " is not less than 5"

 

Single Statement Suites

flag = 1
while (flag): print 'Given flag is really true!'
print "Good bye!"

 

nested loops

i = 2
while(i < 100):
j = 2
while(j <= (i/j)):
if not(i%j): break
j = j + 1
if (j > i/j) : print i, " is prime"
i = i + 1

 

 

Control Statement

Python supports the following control statements.

Control Statement

Description

break statement

Terminates the loop statement and transfers execution to the statement immediately following the loop.

continue statement

Causes the loop to skip the remainder of its body and immediately retest its condition prior to reiterating.

pass statement

The pass statement in Python is used when a statement is required syntactically but you do not want any command or code to execute.

 

break statement

It terminates the current loop and resumes execution at the next statement, just like the traditional break statement in C.
The most common use for break is when some external condition is triggered requiring a hasty exit from a loop. The break statement can be used in both while and for loops.
If you are using nested loops, the break statement stops the execution of the innermost loop and start executing the next line of code after the block.
 
for letter in 'Python': # First Example
if letter == 'h':
break
print 'Current Letter :', letter

var = 10 # Second Example
while var > 0:
print 'Current variable value :', var
var = var -1
if var == 5:
break

 

continue statement

It returns the control to the beginning of the while loop.. The continue statement rejects all the remaining statements in the current iteration of the loop and moves the control back to the top of the loop.
The continue statement can be used in both while and for loops.
 
for letter in 'Python': # First Example
if letter == 'h':
continue
print 'Current Letter :', letter
 
var = 10 # Second Example
while var > 0:
var = var -1
if var == 5:
continue
print 'Current variable value :', var

Current Letter : P
Current Letter : y
Current Letter : t
Current Letter : o
Current Letter : n
Current variable value : 9
Current variable value : 8
Current variable value : 7
Current variable value : 6
Current variable value : 4
Current variable value : 3
Current variable value : 2
Current variable value : 1
Current variable value : 0

 

pass statement

It is used when a statement is required syntactically but you do not want any command or code to execute.
The pass statement is a null operation; nothing happens when it executes. The pass is also useful in places where your code will eventually go, but has not been written yet.
 
for letter in 'Python':
if letter == 'h':
pass
print 'This is pass block'
print 'Current Letter :', letter
 
Current Letter : P
Current Letter : y
Current Letter : t
This is pass block
Current Letter : h
Current Letter : o
Current Letter : n

 

 

 
         
 
 
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