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1. Arrays in Python
Part ||
‫إعداد‬:
‫م‬.‫محمد‬ ‫علي‬

2. objectives
 Sets
 dictionaries

3. Sets
 A set is a collection which is unordered and unindexed. In Python sets are
written with curly brackets ({ })
 Example:
 set1 = {"apple", "banana", "cherry"}
print(set1)
 Note: Sets are unordered, so you cannot be sure in which order the items will
appear.
 set1 = {"apple", "banana", "cherry"}
for x in set1:
print(x)
 Result:
banana
cherry
apple

4. Check if item in sets
 print("banana" in set1)
 Result: (True)
 Change Item: Once a set is created, you cannot change its items, but you
can add new items, by using add() method
 set1 = {"apple", "banana", "cherry"}
set1.add("orange")
print(set1)
 Result:
 {'banana', 'cherry', 'apple', 'orange'}

5. Change values in sets
 Add multiple items to a set, using the update method
 Example:
 set1 = {"apple", "banana", "cherry"}
set1.update(["orange", "mango", "grapes"])
print(set1)
 Result:
{'grapes', 'orange', 'mongo', 'apple', 'cherry', 'banana'}

6. Deleted value from set
 We can use remove(), discard() and pop()
 remove(“item”): if the item not found will show an error
 discard(“item”): if the item not found will not show an error
 pop(): will remove the last item from set
 Note: Sets are unordered, so when using the pop() method, you will not
know which item that gets removed.
 The clear() method empties the set
 The del keyword will delete the set completely
 So, clear() will delete the items from the set but del will delete set from the
memory

7. Join two sets
 There are several ways to join two or more sets in Python.
 We can use union() method returns a new set with all items from both sets
example:
set1 = {"a", "b" , "c"}
set2 = {1, 2, 3}
set3 = set1.union(set2)
print(set3)
 We can use update() method inserts the items in set2 into set1 example:
set1 = {"a", "b" , "c"}
set2 = {1, 2, 3}
set1.update(set2)
print(set1)
 Note: both union() and update() will exclude any duplicate items.

8. Set methods
Method Description
add() Adds an element to the set
clear() Removes all the elements from the set
copy() Returns a copy of the set
difference()
Returns a set containing the difference
between two or more sets
difference_update()
Removes the items in this set that are
also included in another, specified set
discard() Remove the specified item
intersection()
Returns a set, that is the intersection of
two other sets
intersection_update()
Removes the items in this set that are not
present in other, specified set(s)
isdisjoint()
Returns whether two sets have a
intersection or not

9. Set methods cont
 issubset()
Returns whether another set contains this set or not
 issuperset()
Returns whether this set contains another set or not
 pop()
Removes an element from the set
 remove()
Removes the specified element
 symmetric_difference()
Returns a set with the symmetric differences of two sets
 symmetric_difference_update()
inserts the symmetric differences from this set and another
 union()
Return a set containing the union of sets
 update()
Update the set with the union of this set and others

10. Dictionaries
 A dictionary is a collection which is unordered, changeable and indexed. In
Python dictionaries are written with curly brackets, and they have keys and
values.
 Example:
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
print(thisdict)
Result:
{'brand': 'Ford', 'model': 'Mustang', 'year': 1964}

11. Get an item
 You can access the items of a dictionary by referring to its key name, inside
square brackets
 Example:
x = thisdict["model"]
Print(x)
Result:
Mustang
 There is also a method called get() will give the same result
x = thisdict.get(“model”)
Print(x)
Result:
Mustang

12. Change values
 You can change the value of a specific item by referring to its key name
 Example:
 thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
thisdict["year"] = 2020
 This example will change the year to 2020

13. Loops over dictionaries
 The following will give all key names in dictionary:
for x in thisdict:
print(x)
 The following will give all values names in dictionary:
for x in thisdict:
print(thisdict[x])
 We can also use values() function to return values of a dictionary
for x in thisdict.values():
print(x)
 To get both of key and values we use items() method:
for x, y in thisdict.items():
print(x, y)
 X for the key and y for the value

14. Check for items in dictionaries
 if "model" in thisdict:
print("Yes, 'model' is one of the keys in the thisdict dictionary")
 To add item to dictionary we use the following:
thisdict["color"] = "red"
print(thisdict)
 Result:
{'brand': 'Ford', 'model': 'Mustang', 'year': 2020, 'color': 'red'}

15. Removing items
 We can use pop(),popitem(),clear() method and del keyword
 pop(“item”): remove specific key name
 popitem(): will remove the last key, in python 3.7 will remove a random
item
 The del keyword can delete the dictionary completely
del thisdict
 The clear() method empties the dictionary

16. Copy the dictionaries
 If we write dict2=dict1, in this way dict2 will be a reference for dict1 and
any change on dict1 will happened the same change on dict2
 There are ways to make a copy, one way is to use the built-in Dictionary
method copy()
mydict = thisdict.copy()
 Another way to make a copy is to use the built-in method
mydict = dict(thisdict)

17. Nested Dictionaries
 A dictionary can also contain many dictionaries, this is called nested
dictionaries
 Example
myfamily = {
"child1" : {
"name" : “Ali",
"year" : 1995
},
"child2" : {
"name" : “Ghadeer",
"year" : 1994
},
"child3" : {
"name" : “Mohammad",
"year" : 1996
}
}

18. Nested Dictionaries
 Create three dictionaries, than create one dictionary that will contain the other three
dictionaries
 child1 = {
"name" : “Ali",
"year" : 1995
}
child2 = {
"name" : “Ghadeer",
"year" : 1994
}
child3 = {
"name" : “Mohammad",
"year" : 1996
}
myfamily = {
"child1" : child1,
"child2" : child2,
"child3" : child3
}

19. Dictionary Methods
Method Description
clear() Removes all the elements from the dictionary
copy() Returns a copy of the dictionary
fromkeys()
Returns a dictionary with the specified keys and
value
get() Returns the value of the specified key
items()
Returns a list containing a tuple for each key value
pair
keys() Returns a list containing the dictionary's keys
pop() Removes the element with the specified key
popitem() Removes the last inserted key-value pair
setdefault()
Returns the value of the specified key. If the key does
not exist: insert the key, with the specified value
update()
Updates the dictionary with the specified key-value
pairs
values() Returns a list of all the values in the dictionary