Sets

7.3. Sets#

  • Formal mathematical sets

  • Do not have duplicate values

  • Are not ordered

  • Cannot access via index.

  • Useful for doing set operations

  • Can have different data types

A = {0, 2, 4, 6, 8}
B = {1, 2, 3, 4, 5}

7.3.1. Check if a value belongs#

2 in A

True

7.3.2. Union – all values#

A | B

{0, 1, 2, 3, 4, 5, 6, 8}

7.3.3. Intersection – shared values#

A & B

{2, 4}

7.3.4. Difference – order matters#

A - B
B - A

7.3.5. Check Subset#

A = {1, 2, 3, 4, 5}
B = {3, 4}
B < A

True

A = {1, 2, 3, 4, 5}
B = {3, 4}
B <= A

True

A = {1, 2, 3, 4, 5}
B = {3, 4}
B > A

False

7.3.6. Adding a single element#

A = {1, 2, 3, 4, 5}
A.add(6)
print(A)

{1, 2, 3, 4, 5, 6}

A = {1, 2, 3, 4, 5}
A.add(1)
print(A)

{1, 2, 3, 4, 5}

7.3.7. Removing an element#

  • Three ways

7.3.7.1. Discard#

  • Will NOT raise an error if the element being remove is not in set.

A = {1, 2, 3, 4, 5}
A.discard(1)
print(A)
A.discard('P')

{2, 3, 4, 5}

7.3.7.2. Remove#

  • Will raise an error if the element being remove is not in set.

A = {1, 2, 3, 4, 5}
A.remove(1)
print(A)
A.remove('P')

{2, 3, 4, 5}

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
Cell In[11], line 4
      2 A.remove(1)
      3 print(A)
----> 4 A.remove('P')

KeyError: 'P'

7.3.7.3. Pop#

  • Will remove an element

A = {1, 2, 3, 4, 5}
A.pop()

1

7.3.8. Checking if multiple dictionary keys exist#

d1 = dict(a=1, b=2, c=3, d=4)
d2 = dict(b=20, d=40, e=50)
d1.keys() & d2.keys() # this works because dict.keys() returns "set-like" view rather than a list
{'b', 'd'}

{'b', 'd'}

d1 = dict(a=1, b=2, c=3, d=4)
d2 = dict(b=20, d=40, e=50)
d1.keys() <= {'a', 'b', 'c', 'd'}

True

7.3.9. Symmetric difference#

https://en.wikipedia.org/wiki/Symmetric_difference

A = {1, 2, 3, 4, 5}
B = {3, 4}
A ^ B

{1, 2, 5}
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