Decision control units by Python.pptx includes loop, If else, list, tuple and dictionary

Decision Control Statements
• Decision Control Statements: Decision control statements,
Selection/conditional branching Statements: if, if-else, nested
if, if-elif-else statements. Basic loop Structures/Iterative
statements: while loop, for loop, selecting appropriate loop.
Nested loops, The break, continue, pass, else statement used
with loops. Other data types- Tuples, Lists and Dictionary.
Presented By-
Supriya Sarkar

Python Conditions and If statements
• Python supports the usual logical conditions from mathematics:
• Equals: a == b
• Not Equals: a != b
• Less than: a < b
• Less than or equal to: a <= b
• Greater than: a > b
• Greater than or equal to: a >= b
• Example:
• If statement:
a = 33
b = 200
if b > a:
print("b is greater than a")

Indentation
Example
• If statement, without indentation (will raise an error):
a = 33
b = 200
if b > a:
print("b is greater than a") # you will get an error
• Short Hand If
• If you have only one statement to execute, you can put it
on the same line as the if statement.
Example
• One line if statement:
• if a > b: print("a is greater than b")

Elif
• The elif keyword is Python's way of saying "if the
previous conditions were not true, then try this
condition".
Example
a = 33
b = 33
if b > a:
elif a == b:
print("a and b are equal")

Else
• The else keyword catches anything which isn't caught by the
preceding conditions.
Example
a = 200
b = 33
if b > a:
elif a == b:
print("a and b are equal")
else:
print("a is greater than b")

Else..
• You can also have an else without the elif:
Example
a = 200
b = 33
if b > a:
else:
print("b is not greater than a")

Nested If
• You can have if statements inside if statements, this is
called nested if statements.
Example
• x = 41
if x > 10:
print("Above ten,")
if x > 20:
print("and also above 20!")
else:
print("but not above 20.")

The pass Statement
• if statements cannot be empty, but if you for some reason
have an if statement with no content, put in
the pass statement to avoid getting an error.
Example
• a = 33
b = 200
if b > a:
pass

Python While Loops
Python has two primitive loop commands:
• while loops
• for loops
The while Loop
• With the while loop we can execute a set of statements as
long as a condition is true.
• Example
• Print i as long as i is less than 6:
• i = 1
while i < 6:
print(i)
i += 1

The break Statement
• With the break statement we can stop the loop even if the
while condition is true:
Example
• Exit the loop when i is 3:
• i = 1
while i < 6:
print(i)
if i == 3:
break
i += 1

The continue Statement
• With the continue statement we can stop the current
iteration, and continue with the next:
Example
• Continue to the next iteration if i is 3:
• i = 0
while i < 6:
i += 1
if i == 3:
continue
print(i)

The else Statement
• With the else statement we can run a block of code once
when the condition no longer is true:
Example:
• Print a message once the condition is false:
• i = 1
while i < 6:
print(i)
i += 1
else:
print("i is no longer less than 6")

Python For Loops
• A for loop is used for iterating over a sequence (that is either a
list, a tuple, a dictionary, a set, or a string).
• This is less like the for keyword in other programming
languages, and works more like an iterator method as found in
other object-orientated programming languages.
Example:
• Print each fruit in a fruit list:
• fruits = ["apple", "banana", "cherry"]
for x in fruits:
print(x)

Looping Through a String
• Even strings are iterable objects, they contain a sequence of
characters:
Example
• Loop through the letters in the word "banana":
• for x in "banana":
print(x)

The break Statement
for loop
• With the break statement we can stop the loop before it has
looped through all the items:
Example
• Exit the loop when x is "banana":
for x in fruits:
print(x)
if x == "banana":
break

The continue Statement
• With the continue statement we can stop the current
iteration of the loop, and continue with the next:
Example
• Do not print banana:
for x in fruits:
if x == "banana":
continue
print(x)

The range() Function
• To loop through a set of code a specified number of times, we
can use the range() function,
• The range() function returns a sequence of numbers, starting
from 0 by default, and increments by 1 (by default), and ends
at a specified number.
Example
• Using the range() function:
• for x in range(6):
print(x)
Note: that range(6) is not the values of 0 to 6, but the values 0
to 5.

range() function…
• The range() function defaults to 0 as a starting value, however
it is possible to specify the starting value by adding a
parameter: range(2, 6), which means values from 2 to 6 (but
not including 6):
Example
• Using the start parameter:
• for x in range(2, 6):
print(x)

range() function..
• The range() function defaults to increment the sequence by 1,
however it is possible to specify the increment value by adding
a third parameter: range(2, 30, 3):
Example
• Increment the sequence with 3 (default is 1):
• for x in range(2, 30, 3):
print(x)

Python Tuples
• Tuples are used to store multiple items in a single
variable. Tuple is imutable
• A tuple is a collection which is ordered
and unchangeable.
• Tuples are written with round brackets.
Example
• Create a Tuple:
• thistuple = ("apple", "banana", "cherry")
print(thistuple)

Tuple Items
• Tuple items are ordered, unchangeable, and allow duplicate values.
• Tuple items are indexed, the first item has index [0], the second item has
index [1] etc.
Ordered
• When we say that tuples are ordered, it means that the items have a defined
order, and that order will not change.
Unchangeable
• Tuples are unchangeable, meaning that we cannot change, add or remove
items after the tuple has been created.
Allow Duplicates
• Since tuples are indexed, they can have items with the same value:
Example
• Tuples allow duplicate values:
• thistuple = ("apple", "banana", "cherry", "apple", "cherry")
print(thistuple)

Tuple Items - Data Types
• Tuple items can be of any data type:
Example
• String, int and boolean data types:
• tuple1 = ("apple", "banana", "cherry")
tuple2 = (1, 5, 7, 9, 3)
tuple3 = (True, False, False)
Example
• A tuple with strings, integers and boolean values:
• tuple1 = ("abc", 34, True, 40, "male")
Example
• What is the data type of a tuple?
• mytuple = ("apple", "banana", "cherry")
print(type(mytuple))

Access Tuple Items
• You can access tuple items by referring to the index number,
inside square brackets:
Example
• Print the second item in the tuple:
print(thistuple[1])
Negative Indexing
• Negative indexing means start from the end.
• -1 refers to the last item, -2 refers to the second last item etc.
Example
• Print the last item of the tuple:
print(thistuple[-1])

Range of Indexes
• You can specify a range of indexes by specifying where to
start and where to end the range.
• When specifying a range, the return value will be a new
tuple with the specified items.
Example
• Return the third, fourth, and fifth item:
• thistuple =
("apple", "banana", "cherry", "orange", "kiwi", "melon", "
mango")
print(thistuple[2:5])

Python - Update Tuples
• Tuples are unchangeable, meaning that you cannot change,
add, or remove items once the tuple is created.
• But there are some workarounds.
• Once a tuple is created, you cannot change its values. Tuples
are unchangeable, or immutable as it also is called.
Example
• Convert the tuple into a list to be able to change it:
• x = ("apple", "banana", "cherry")
y = list(x)
y[1] = "kiwi"
x = tuple(y)
print(x)

Add Items/ del items
Example
• Convert the tuple into a list, add "orange", and convert it back into a
tuple:
y = list(thistuple)
y.append("orange")
thistuple = tuple(y)
Example
• The del keyword can delete the tuple completely:
del thistuple
print(thistuple) #this will raise an error because the tuple no longer
exists

Python –Pack/ Unpack Tuples
• When we create a tuple, we normally assign values to it. This is
called "packing" a tuple:
Example
• Packing a tuple:
• fruits = ("apple", "banana", "cherry")
Example
• Unpacking a tuple:
• fruits = ("apple", "banana", "cherry")
(green, yellow, red) = fruits
print(green)
print(yellow)
print(red)

Python - Join Tuples
• Join Two Tuples
• To join two or more tuples you can use the + operator:
Example
• Join two tuples:
• tuple1 = ("a", "b" , "c")
tuple2 = (1, 2, 3)
tuple3 = tuple1 + tuple2
print(tuple3)

Exercise:
• Print the first item in the fruits tuple.
fruits = ("apple", "banana", "cherry")
print()

Python Lists
• Lists are used to store multiple items in a single variable.
• Lists are created using square brackets:
Example
• Create a List:
• thislist = ["apple", "banana", "cherry"]
print(thislist)

List..
• List items are ordered, changeable, and allow duplicate values.
• List items are indexed, the first item has index [0], the second item has
index [1] etc.
• Ordered
• When we say that lists are ordered, it means that the items have a defined
order, and that order will not change.
• If you add new items to a list, the new items will be placed at the end of the
list.
• Changeable
• The list is changeable, meaning that we can change, add, and remove items
in a list after it has been created.
•
Allow Duplicates
• Since lists are indexed, lists can have items with the same value:
Example
• Lists allow duplicate values:
• thislist = ["apple", "banana", "cherry", "apple", "cherry"]
print(thislist)

Python - Access List Items
• List items are indexed and you can access them by referring to the
index number:
Example
• Print the second item of the list:
print(thislist[1])
Negative Indexing
• Negative indexing means start from the end
• -1 refers to the last item, -2 refers to the second last item etc.
Example
• Print the last item of the list:
print(thislist[-1])

Python - Change List Items
• To change the value of a specific item, refer to the index number:
Example
• Change the second item:
thislist[1] = "blackcurrant"
print(thislist)
Insert Items
• To insert a new list item, without replacing any of the existing
values, we can use the insert() method.
• The insert() method inserts an item at the specified index:
Example
• Insert "watermelon" as the third item:
thislist.insert(2, "watermelon")
print(thislist)

Python - Add List Items
Append Items
• To add an item to the end of the list, use the append() method:
Example
• Using the append() method to append an item:
thislist.append("orange")
print(thislist)
Insert Items
• To insert a list item at a specified index, use the insert() method.
• The insert() method inserts an item at the specified index:
• Example
• Insert an item as the second position:
thislist.insert(1, "orange")
print(thislist)

Extend List
• To append elements from another list to the current list, use
the extend() method.
Example
• Add the elements of tropical to thislist:
tropical = ["mango", "pineapple", "papaya"]
thislist.extend(tropical)
print(thislist)
Remove Specified Item
• The remove() method removes the specified item.
Example
• Remove "banana":
thislist.remove("banana")
print(thislist)

List..
• The pop() method removes the specified index.
Example
• Remove the second item:
thislist.pop(1)
print(thislist)
• The del keyword also removes the specified index:
Example
• Remove the first item:
del thislist[0]
print(thislist)

Python - Loop Lists
• You can loop through the list items by using a for loop:
Example
• Print all items in the list, one by one:
for x in thislist:
print(x)
Loop Through the Index Numbers
• You can also loop through the list items by referring to their index
number.
• Use the range() and len() functions to create a suitable iterable.
Example
• Print all items by referring to their index number:
for i in range(len(thislist)):
print(thislist[i])

Looping Using List Comprehension
• List Comprehension offers the shortest syntax for looping through lists:
Example
• A short hand for loop that will print all items in a list:
[print(x) for x in thislist]
Example
• fruits = ["apple", "banana", "cherry", "kiwi", "mango"]
newlist = []
for x in fruits:
if "a" in x:
newlist.append(x)
print(newlist)
With list comprehension you can do all that with only one line of code:
Example
• fruits = ["apple", "banana", "cherry", "kiwi", "mango"]
newlist = [x for x in fruits if "a" in x]
print(newlist)

Python - Sort Lists
• Sort List Alphanumerically
• List objects have a sort() method that will sort the list alphanumerically,
ascending, by default:
Example
• Sort the list alphabetically:
• thislist = ["orange", "mango", "kiwi", "pineapple", "banana"]
thislist.sort()
print(thislist)
• Sort Descending
• To sort descending, use the keyword argument reverse = True:
Example
• Sort the list descending:
• thislist = ["orange", "mango", "kiwi", "pineapple", "banana"]
thislist.sort(reverse = True)
print(thislist)

Python - Copy Lists
Copy a List
• You cannot copy a list simply by typing list2 = list1,
because: list2 will only be a reference to list1, and
changes made in list1 will automatically also be made
in list2.
• There are ways to make a copy, one way is to use the
built-in List method copy().
Example
• Make a copy of a list with the copy() method:
mylist = thislist.copy()
print(mylist)

Python - Join Lists
• Join Two Lists
• There are several ways to join, or concatenate, two or
more lists in Python.
• One of the easiest ways are by using the + operator.
Example
• Join two list:
• list1 = ["a", "b", "c"]
list2 = [1, 2, 3]
list3 = list1 + list2
print(list3)

Python Dictionaries
Dictionary
• Dictionaries are used to store data values in key:value pairs.
• A dictionary is a collection which is ordered*, changeable and
do not allow duplicates.
Example
• Create and print a dictionary:
• thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
print(thisdict)

Dictionary Items
• Dictionary items are ordered, changeable, and does not
allow duplicates.
• Dictionary items are presented in key:value pairs, and can
be referred to by using the key name.
Example
• Print the "brand" value of the dictionary:
• thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
print(thisdict["brand"])

Dictionary..
Ordered or Unordered?
• When we say that dictionaries are ordered, it means that the items
have a defined order, and that order will not change.
Changeable
• Dictionaries are changeable, meaning that we can change, add or
remove items after the dictionary has been created.
Duplicates Not Allowed
• Dictionaries cannot have two items with the same key:
Example
• Duplicate values will overwrite existing values:
• thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964,
"year": 2020
}
print(thisdict)

Dictionary..
Dictionary Length
• To determine how many items a dictionary has, use
the len() function:
Example
• Print the number of items in the dictionary:
• print(len(thisdict))
The dict() Constructor
• It is also possible to use the dict() constructor to make a
dictionary.
Example
• Using the dict() method to make a dictionary:
• thisdict = dict(name = "John", age = 36, country = "Norway")
print(thisdict)

Python - Access Dictionary Items
• Accessing Items
• You can access the items of a dictionary by referring to its
key name, inside square brackets:
Example
• Get the value of the "model" key:
• thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
x = thisdict["model"]

Get Keys
• The keys() method will return a list of all the keys in the dictionary.
Example
• Get a list of the keys:
• x = thisdict.keys()
Get Values
• The values() method will return a list of all the values in the dictionary.
Example
• Get a list of the values:
• x = thisdict.values()
Get Items
• The items() method will return each item in a dictionary, as tuples in a list.
Example
• Get a list of the key:value pairs
• x = thisdict.items()

Update Dictionary
• The update() method will update the dictionary with the
items from the given argument.
• The argument must be a dictionary, or an iterable object
with key:value pairs.
Example
• Update the "year" of the car by using
the update() method:
• thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
thisdict.update({"year": 2020})

Python - Remove Dictionary Items
• Removing Items
• There are several methods to remove items from a dictionary:
Example
• The pop() method removes the item with the specified key name:
• thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
thisdict.pop("model")
print(thisdict)
Example
• The del keyword removes the item with the specified key name:
• thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
del thisdict["model"]
print(thisdict)

Python - Loop Dictionaries
• Loop Through a Dictionary
• You can loop through a dictionary by using a for loop.
• When looping through a dictionary, the return value are the keys of the dictionary, but
there are methods to return the values as well.
Example
• Print all key names in the dictionary, one by one:
• for x in thisdict:
print(x)
Example
• You can also use the values() method to return values of a dictionary:
• for x in thisdict.values():
print(x)
Example
• You can use the keys() method to return the keys of a dictionary:
• for x in thisdict.keys():
print(x)
Example
• Loop through both keys and values, by using the items() method:
• for x, y in thisdict.items():
print(x, y)

Python - Nested Dictionaries
• A dictionary can contain dictionaries, this is called nested dictionaries.
Example
• Create a dictionary that contain three dictionaries:
• myfamily = {
"child1" : {
"name" : "Emil",
"year" : 2004
},
"child2" : {
"name" : "Tobias",
"year" : 2007
},
"child3" : {
"name" : "Linus",
"year" : 2011
}
}

Dictionary..
Access Items in Nested Dictionaries
• To access items from a nested dictionary, you use the name of
the dictionaries, starting with the outer dictionary:
Example
• Print the name of child 2:
• print(myfamily["child2"]["name"])
Exercise:
• Use the get method to print the value of the "model" key of
the car dictionary.
• car = { "brand": "Ford", "model": "Mustang", "year": 1964 }
print()

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