3.4. Sequence Frozenset¶

3.4.1. Rationale¶

Only unique values

Immutable - cannot add, modify or remove items

Can store elements of any hashable types

Has all set methods such as .intersect(), .subset() .union(), etc.

One solid block in memory

3.4.2. Type Definition¶

Frozenset is unordered data structure

Do not support getitem

Do not support slice

Defining only with frozenset() - no short syntax

Comma after last element of a one element frozenset is optional

Brackets are required

Listing 3.9. set type definition¶

data = frozenset()

data = frozenset({1})
data = frozenset({1, 2, 3})
data = frozenset({1.1, 2.2, 3.3})
data = frozenset({True, False})
data = frozenset({'a', 'b', 'c'})
data = frozenset({'a', 1, 2.2, True, None})

3.4.3. Type Casting¶

frozenset() converts argument to frozenset

data = [1, 2, 3]
frozenset(data)
# frozenset({1, 2, 3})

data = (1, 2, 3)
frozenset(data)
# frozenset({1, 2, 3})

data = {1, 2, 3}
frozenset(data)
# frozenset({1, 2, 3})

data = frozenset({1, 2, 3})
frozenset(data)
# frozenset({1, 2, 3})

data = [1, 2, 3, [4, 5]]
frozenset(data)
# TypeError: unhashable type: 'list'

data = [1, 2, 3, (4, 5)]
frozenset(data)
# frozenset({(4, 5), 1, 2, 3})

3.4.4. Frozenset or Set¶

Both:

unordered

impossible to getitem and slice

unique elements

only hashable elements

Frozenset:

immutable

one contingent block of data in memory

Set:

mutable

implemented in memory as list of pointers to objects

objects are scattered in memory

3.4.5. Assignments¶

3.4.5.1. Sequence Frozenset Create¶

Complexity level: easy
Lines of code to write: 3 lines
Estimated time of completion: 3 min
Solution: solution/sequence_frozenset_create.py

English

Create frozenset result with elements:
- 'a'
- 1
- 2.2
Print result
Print number of elements in result

Polish

Stwórz frozenset result z elementami:
- 'a'
- 1
- 2.2
Wypisz result
Wypisz liczbę elementów result

The whys and wherefores

Defining list

3.4.5.2. Sequence Frozenset Newline¶

Complexity level: easy
Lines of code to write: 2 lines
Estimated time of completion: 3 min
Solution: solution/sequence_frozenset_newline.py

English

Use data from "Input" section (see below)
Define result: str
Use str.join() to join lines of text with newline (\n) character
Compare result with "Output" section (see below)

Polish

Użyj danych z sekcji "Input" (patrz poniżej)
Zdefiniuj result: str
Użyj str.join() aby połączyć linie tekstu znakiem końca linii (\n)
Porównaj wyniki z sekcją "Output" (patrz poniżej)

Input

DATA = frozenset({
    'We choose to go to the Moon.',
    'We choose to go to the Moon in this decade and do the other things.',
    'Not because they are easy, but because they are hard.'})

Output

result: str
# 'We choose to go to the Moon.\nWe choose to go to the Moon in this decade and do the other things.\nNot because they are easy, but because they are hard.'