Note_Tech

All technological notes.

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Python - Set

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• Python - Set
  • Set
    • Set Methods
    • Create a set
    • Add Items
      • add(): adds an element
      • update(): adding items from another iterable.
    • Remove Item
      • discard(value)
      • pop()
      • remove(item)
      • clear()
      • del Operator
  • copy(): copies the set
  • Loop Set
  • in Operator: Check if Item Exists

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Set

• Sets are used to store multiple items in a single variable.

• Unordered

  • the items in a set do not have a defined order.
  • the items cannot be referred to by index or key.

• Unchangeable

  • Set items cannot be changed after the set has been created.
  • Once a set is created, items can be removed and new items can be added.

• Duplicates Not Allowed

  • Sets cannot have two items with the same value.
  • The values True and 1 are considered the same value in sets, and are treated as duplicates.

  xset = {"apple", "banana", "cherry", True, 1, 2}
  print(xset)     # {'apple', True, 2, 'banana', 'cherry'}
  

• Data Types

  • Set items can be of any data type.

  xset = {"abc", 34, True, 40, "male"}
  print(xset)     # {True, 34, 'abc', 40, 'male'}
  

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Set Methods

• Create a Set

Method	Description
set()	return a set

• Copy a Set

Method	Description
set()	return a set
copy()	Returns a copy of the set

• Add items

Method	Description
add()	Adds an element to the set

• Update items

Method	Description
update()	Update the set with the union of this set and others
difference_update()	Removes the items in this set that are also included in another, specified set
intersection_update()	Removes the items in this set that are not present in other, specified set(s)
symmetric_difference_update()	inserts the symmetric differences from this set and another

• Remove items

Method	Description
pop()	Removes an element from the set
remove()	Removes the specified element
discard()	Remove the specified item
clear()	Removes all the elements from the set

• Set calcuation

Method	Description
difference()	Returns a set containing the difference between two or more sets
intersection()	Returns a set, that is the intersection of two other sets
isdisjoint()	Returns whether two sets have a intersection or not
issubset()	Returns whether another set contains this set or not
issuperset()	Returns whether this set contains another set or not
symmetric_difference()	Returns a set with the symmetric differences of two sets
union()	Return a set containing the union of sets

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Create a set

• 1. curly brackets.
• 1. set() Constructor

# create a set

print("\n--------Create a Set--------\n")
# using curly brackets
xset = {"apple", "banana", "cherry"}
print(xset)     # {'apple', 'banana', 'cherry'}


# using set() constructor
xset = set(("apple", "banana", "cherry"))  # note the double round-brackets
print(xset)     # {'cherry', 'banana', 'apple'}

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Add Items

add(): adds an element

• add(): add one item to a set

print("\n--------Add a Item:add()--------\n")
xlist = {"apple", "banana", "cherry"}
xlist.add("orange")
print(xlist)    # {'cherry', 'orange', 'apple', 'banana'}

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update(): adding items from another iterable.

• update(): add items from another set into the current set.
  • does not have to be a set, it can be any iterable object (tuples, lists, dictionaries etc.).

print("\n---------Add items: update()--------\n")
xset = {"apple", "banana", "cherry"}
yset = {"pineapple", "mango", "papaya"}
xset.update(yset)

print(xset)     # {'papaya', 'banana', 'apple', 'cherry', 'pineapple', 'mango'}

zset = xset.update(yset)
print(zset)     # None

# iterable object
xset = {"apple", "banana", "cherry"}
yset = ["pineapple", "mango", "papaya"]
xset.update(yset)

print(xset)     # {'papaya', 'banana', 'apple', 'cherry', 'pineapple', 'mango'}

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Remove Item

discard(value)

• remove an item in a set

  • If the item to remove does not exist, discard() will NOT raise an error.

# .discard()
xset = {"apple", "banana", "cherry"}
xset.discard("banana")
print(xset)

xset.discard("banana")
xset.discard("banana")

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pop()

• remove a random item

  • return value: the removed item.

# .pop()
xset = {"apple", "banana", "cherry"}
x = xset.pop()            #
# x = xset.pop(1)           # TypeError: set.pop() takes no arguments (1 given)
# x = xset.pop("banana")    # TypeError: set.pop() takes no arguments (1 given)
print(xset)
print(x)                    # a random item removed from set

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remove(item)

• remove an item in a set

  • If the item to remove does not exist, remove() will raise an error.

# .remove()
xset = {"apple", "banana", "cherry"}
xset.remove("banana")
print(xset)

# xset.remove("banana")       # KeyError: 'banana'

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clear()

• empties the set

# clear()
xset = {"apple", "banana", "cherry"}
xset.clear()

print(xset)     # set()

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del Operator

• delete the tuple completely

# del
xset = {"apple", "banana", "cherry"}
del xset

# print(xset)     # NameError: name 'xset' is not defined

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copy(): copies the set

• copies the set

x_set = {"apple", "banana", "cherry"}
y_set = x_set.copy()
print(y_set)    # {'banana', 'apple', 'cherry'}

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Loop Set

• for in loop

print("\n--------for in loop--------\n")
# for in loop
xset = {"apple", "banana", "cherry"}
for x in xset:
    print(x)

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in Operator: Check if Item Exists

xlist = {"apple", "banana", "cherry"}
if "apple" in xlist:
  print("Yes, 'apple' is in the fruits list")

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