ppt3-conditionalstatementloopsdictionaryfunctions-240731050730-455ba0fa.ppt

Rahul Kumar
CS Deptt. KIET
rahul.kumar@kiet.edu
Conditional statement
Bibek Kumar-Assistant Professor-CSE,
KIET

If, elif, else statement
KIET
if Statements in Python allows us to tell the computer to perform alternative actions based on a
certain set of results.
Verbally, we can imagine we are telling the computer:
"Hey if this case happens, perform some action"
We can then expand the idea further with elif and else statements, which allow us to tell the
computer:
"Hey if this case happens, perform some action. Else, if another case happens, perform some other
action. Else, if none of the above cases happened, perform this action."
If the condition "condition_1" is True, the statements of the block
statement_block_1 will be executed. If not, condition_2 will be
evaluated. If condition_2 evaluates to True, statement_block_2 will
be executed, if condition_2 is False, the other conditions of the
following elif conditions will be checked, and finally if none of them
has been evaluated to True, the indented block below the else
keyword will be executed.

KIET
The if, elif and else Statements
Examples Multiple Branches
Note how the nested if statements are each checked until a
True Boolean causes the nested code below it to run. We should
also note that we can put in as many elif statements as we want
before we close off with an else.

While
KIET
The while statement in Python is one of most general ways to perform
iteration. A while statement will repeatedly execute a single statement or
group of statements as long as the condition is true. The reason it is called a
'loop' is because the code statements are looped through over and over
again until the condition is no longer met.
Notice how many times the print statements
occurred and how the while loop kept going until
the True condition was met, which occurred once
x==10. It's important to note that once this
occurred the code stopped.

While Loops
We can also add else statement in the loop as shown
When the loop completes, the else statement is read
5

While Loops
We can use break, continue, and pass statements in our loops to add additional functionality for
various cases. The three statements are defined by:
•break: Breaks out of the current closest enclosing loop.
•continue: Goes to the top of the closest enclosing loop.
•pass: Does nothing at all.
Syntax:
while test:
code
statement
if test:
break
if test:
continue
else:
break and continue statements can appear anywhere inside the loop’s body, but we will usually
put them further nested in conjunction with an if statement to perform an action based on
some condition.
A word of caution however! It is possible to create an
infinitely running loop with while statements.
6

A for loop acts as an iterator in Python; it goes through items
that are in a sequence or any other iterable item. Objects that
we've learned about that we can iterate over include strings,
lists, tuples, and even built-in iterables for dictionaries, such as
keys or values.
for item in object:
statements to do
stuff
Example
Let's print only the even numbers from that list!
We could have also put an else statement in there
7
For loop

Using the for Statement
Another common idea during a for loop is keeping some sort of
running tally during multiple loops
We've used for loops with lists, how about with strings?
Remember strings are a sequence so when we iterate through
them we will be accessing each item in that string.
Let's now look at how a for loop can be used with a tuple
Tuples are very similar to lists, however, unlike lists they are
immutable meaning they can not be changed. You would use
tuples to present things that shouldn't be changed, such as days
of the week, or dates on a calendar.
The construction of a tuples use () with elements separated by
commas.
8

Using the for Statement
Tuples have a special quality when it comes to for loops. If you
are iterating through a sequence that contains tuples, the item
can actually be the tuple itself, this is an example of tuple
unpacking. During the for loop we will be unpacking the tuple
inside of a sequence and we can access the individual items
inside that tuple!
Iterating through Dictionaries
9

Break statement
• Used to terminate the execution of the nearest enclosing loop .
• It is widely used with for and while loop
Example
I = 1
while I <= 10:
print(I, end=“ “)
if I==5:
break
I = I+1
Print (“Out from while loop”)
10

Continue statement
• The Continue statement is used to skip the rest of the code inside a
loop for the current iteration only. Loop does not terminate but
continues on with the next iteration.
Example
for val in "string":
if val == "i":
continue
print(val)
print("The end")
11

Range() function
12
The range() is an in-built function in Python. It returns a sequence
of numbers starting from zero and increment by 1 by default and
stops before the given number.
x = range(5)
for n in x:
print(n)
Example : range(5) will start from 0 and end at 4.
range(start, stop, step)

Range() function
13
Along with loops, range() is also used to iterate over the list types using
the len function and access the values through the index
Example
listType = ['US', 'UK', 'India', 'China']
for i in range(len(listType)):
print(listType[i])
Reverse Range
•We can give either positive or negative numbers for any of the
parameters in the range.
•This feature offers the opportunity to implement reverse loops.
•We can do this by passing a higher index as a start and a negative step
value.
for i in range(10, 5, -1):
print(i) #OutPut : 10, 9, 8, 7, 6

Range() function
14
Create List, Set and Tuple using Range
range() comes handy in many situations, rather than only using to write
loops.
For example, we create List, Set, and Tuple using range function instead
of using loops to avoid boilerplate code.
Example:
print(list(range(0, 10, 2)))
print(set(range(0, 10, 2)))
print(tuple(range(0, 10, 2)))
print(list(range(10, 0, -2)))
print(tuple(range(10, 0, -2)))

pass statement
•In Python programming, pass is a null statement.
•The difference between a comment and pass statement in Python is that,
while the interpreter ignores a comment entirely, pass is not ignored.
•However, nothing happens when pass is executed. It results into no
operation (NOP).
•Suppose we have a loop or a function that is not implemented yet, but we
want to implement it in the future. They cannot have an empty body. So, we
use the pass statement to construct a body that does nothing.
•Example
sequence = {‘p’, ‘a’, ‘s’, ‘s’}
for val in sequence:
pass

Lambda OR Anonymous function
They are not declared as normal function.
They do not required def keyword but they are declared with a lambda
keyword.
Lambda function feature added to python due to
Demand from LISP programmers.
Syntax: lambda argument1,argument2,….argumentN: expression
Example:
Sum = lambda x,y : x+y

Program:
Program that passes lambda function as an argument to a function
def func(f, n):
print(f(n))
Twice = lambda x:x *2
Thrice = lambda y:y*3
func(Twice, 5)
func(Thrice,6)
Output: 10
18

Functional programming decomposes a problem into set of functions.
1.filter( )
This function is responsible to construct a list from those elements of the list
for which a function returns True.
Syntax: filter (function, sequence)
Example:
def check(x):
if(x%2==0 or x%4==0):
return 1
evens = list(check, range(2,22))
print(evens)
O/P: [2,4,6,8…….16,18,20]
Functional Programming

2. map():
It applies a particular function to every element of a list.
Its syntax is similar to filter function
After apply the specified function on the sequence the map() function
return the modified list.
map(function, sequence)
Example:
def mul_2(x):
x*=2
return x
num_list = [1,2,3,4,5,6,7]
New_list = list(map(mul_2, num_list)
Print(New_list)

2. reduce():
It returns a single value generated by calling the function on the first two
items of the sequence then on result and the next item, and so on.
Syntax: reduce(function, sequence)
Example:
import functools
def add(a,b):
return x,y
num_list = [1,2,3,4,5]
print(functools.reduce(add, num_list))

List comprehension offers a shorter syntax when we want to create a new
list
Based on the values of an existing list.
Example
Fruits = [“apple”, “banana”, “cherry”, “kiwi”, “mango”]
newlist = [ ]
for x in Fruits:
if “a” in x:
newlist.append(x)
Print(newlist)
List Comprehension

Strings
•A string is a sequence of characters.
•Computers do not deal with characters, they deal with numbers (binary).
Even though you may see characters on your screen, internally it is stored
and manipulated as a combination of 0’s and 1’s.
•How to create a string?
•Strings can be created by enclosing characters inside a single quote or
double quotes.
•Even triple quotes can be used in Python but generally used to represent
multiline strings and docstrings.
myString = ‘Hello’
print(myString) myString = "Hello"
print(myString) myString = ‘’’Hello’’’
print(myString)

How to access characters in a string?
myString = "Hello"
#print first Character
print(myString[0])
#print last character using negative indexing
print(myString[-1])
#slicing 2nd to 5th character
print(myString[2:5])
#print reverse of string
print(myString[::-1])
How to change or delete a string ?
•Strings are immutable.
•We cannot delete or remove characters from a string. But deleting the
string entirely is possible using the keyword del.

String Operations
•Concatenation
s1 = "Hello "
s2 = “KNMIET"
#concatenation of 2 strings
print(s1 + s2)
#repeat string n times
print(s1 * 3)
•Iterating Through String
count = 0
for l in "Hello World":
if l == "o":
count += 1
print(count, " letters found")

String Membership Test
•To check whether given character or string is present or not.
•For example-
print("l" in "Hello World")
print("or" in "Hello World")
•String Methods
•lower()
•join()
•split()
•upper()

Python Program to Check whether a String is
Palindrome or not ?
myStr = "Madam"
#convert entire string to either lower or upper
myStr = myStr.lower()
#reverse string
revStr = myStr[::-1]
#check if the string is equal to its reverse
if myStr == revStr:
print("Given String is palindrome")
else:
print("Given String is not palindrome")

Python Program to Sort Words in Alphabetic Order?
myStr = "python Program to Sort words in Alphabetic Order"
#breakdown the string into list of words
words = myStr.split()
#sort the list
words.sort()
#printing Sorted words
for word in words:
print(word)

ppt3-conditionalstatementloopsdictionaryfunctions-240731050730-455ba0fa.ppt

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