6.4. Iterable Nested

  • Iterable is an object

  • Iterable element is an object too

  • Therefore an element of a Iterable could be another Iterable

  • There is no limit how nested it could be

6.4.1. What is an Object?

  • Basic types are objects

  • Iterable are objects too

  • Everything is an object

  • tuple.mro()

  • list.mro()

  • set.mro()

>>> tuple.mro()
[<class 'tuple'>, <class 'object'>]

>>> list.mro()
[<class 'list'>, <class 'object'>]

>>> set.mro()
[<class 'set'>, <class 'object'>]

6.4.2. List of Lists

  • Also known as multidimensional lists or matrix

Readability differs depending on whitespaces:

>>> a = [[1,2,3],[4,5,6],[7,8,9]]

>>> b = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

>>> c = [[1,2,3], [4,5,6], [7,8,9]]

>>> d = [
...      [1, 2, 3],
...      [4, 5, 6],
...      [7, 8, 9],
... ]

>>> e = [
...      [1, 2, 3],
...      [4, 5, 6],
...      [7, 8, 9]]

>>> f = [[1, 2, 3],
...      [4, 5, 6],
...      [7, 8, 9],
... ]

>>> g = [[1, 2, 3],
...      [4, 5, 6],
...      [7, 8, 9]]

6.4.3. List of Tuples

Readability differs depending on whitespaces:

>>> data = [
...     ('Mark', 'Watney'),
...     ('Melisa', 'Lewis'),
...     ('Rick', 'Martinez'),
... ]

>>> data = [
...     ('Mark', 'Watney'),
...     ('Melisa', 'Lewis'),
...     ('Rick', 'Martinez')]

>>> data = [('Mark', 'Watney'),
...         ('Melisa', 'Lewis'),
...         ('Rick', 'Martinez')]

6.4.4. List of Dicts

>>> data = [
...     {'firstname': 'Mark', 'lastname': 'Watney'},
...     {'firstname': 'Melisa', 'lastname': 'Lewis'},
...     {'firstname': 'Rick', 'lastname': 'Martinez'},
... ]

6.4.5. Many Types

Content could be even more complex data structure with nested items:

>>> data = {
...     'firstname': 'Mark',
...     'lastname': 'Watney',
...     'birthdate': '2000-01-02',
...     'age': 24,
...     'cities': ('Houston', 'Pasadena'),
...     'states': ['Texas', 'California'],
...     'groups': {'users', 'staff', 'admin'},
...     'friends': [
...         {'firstname': 'Melissa', 'lastname': 'Lewis'},
...         {'firstname': 'Rick', 'lastname': 'Martinez'},
...         {'firstname': 'Alex', 'lastname': 'Vogel'},
...         {'firstname': 'Beth', 'lastname': 'Johanssen'},
...         {'firstname': 'Chris', 'lastname': 'Beck'},
...     ],
... }

6.4.6. Length

>>> data = [
...     ('Mark', 'Watney'),
...     ('Melisa', 'Lewis'),
...     ('Rick', 'Martinez'),
... ]

>>> len(data)
3

>>> len(data[0])
2

>>> len(data[0][1])
6

6.4.7. Append vs. Extend

>>> from pprint import pprint

>>> data = [1, 2, 3]
>>> data.extend([4, 5, 6])
>>>
>>> data
[1, 2, 3, 4, 5, 6]

>>> data = [1, 2, 3]
>>> data.append([4, 5, 6])
>>>
>>> data
[1, 2, 3, [4, 5, 6]]

Append elements using list.append():

>>> result = [
...     ('Mark', 'Watney'),
...     ('Melisa', 'Lewis'),
...     ('Rick', 'Martinez'),
... ]
>>>
>>> data = ('Alex', 'Vogel')
>>> result.append(data)
>>>
>>> pprint(result, width=30)
[('Mark', 'Watney'),
 ('Melisa', 'Lewis'),
 ('Rick', 'Martinez'),
 ('Alex', 'Vogel')]

Append elements using list.extend():

>>> result = [
...     ('Mark', 'Watney'),
...     ('Melisa', 'Lewis'),
...     ('Rick', 'Martinez'),
... ]
>>>
>>> data = ('Alex', 'Vogel')
>>> result.extend(data)
>>>
>>> pprint(result, width=30)
[('Mark', 'Watney'),
 ('Melisa', 'Lewis'),
 ('Rick', 'Martinez'),
 'Alex',
 'Vogel']

6.4.8. Use Case - 1

  • One dimensional (1D) structure - vector

>>> data = [1, 2, 3]

Is equivalent to:

>>> obj1 = 1
>>> obj2 = 2
>>> obj3 = 3
>>>
>>> data = [obj1, obj2, obj3]

6.4.9. Use Case - 2

  • Two dimensional (2D) structure - matrix

>>> data = [
...      [1, 2, 3],
...      [4, 5, 6],
...      [7, 8, 9],
... ]

Is equivalent to:

>>> obj1 = [1, 2, 3]
>>> obj2 = [4, 5, 6]
>>> obj3 = [7, 8, 9]
>>>
>>> data = [obj1, obj2, obj3]

6.4.10. Assignments

# %% License
# - Copyright 2025, Matt Harasymczuk <matt@python3.info>
# - This code can be used only for learning by humans
# - This code cannot be used for teaching others
# - This code cannot be used for teaching LLMs and AI algorithms
# - This code cannot be used in commercial or proprietary products
# - This code cannot be distributed in any form
# - This code cannot be changed in any form outside of training course
# - This code cannot have its license changed
# - If you use this code in your product, you must open-source it under GPLv2
# - Exception can be granted only by the author

# %% Run
# - PyCharm: right-click in the editor and `Run Doctest in ...`
# - PyCharm: keyboard shortcut `Control + Shift + F10`
# - Terminal: `python -m doctest -v myfile.py`

# %% About
# - Name: Iterable Nested Definition
# - Difficulty: easy
# - Lines: 4
# - Minutes: 3

# %% English
# 1. Create nested list `result` with elements:
#    - tuple: 1, 2, 3
#    - list: 1.1, 2.2, 3.3
#    - set: 'red', 'green', 'blue'
# 2. Run doctests - all must succeed

# %% Polish
# 1. Stwórz zagnieżdżoną listę `result` z elementami:
#    - tuple: 1, 2, 3
#    - list: 1.1, 2.2, 3.3
#    - set: 'red', 'green', 'blue'
# 2. Uruchom doctesty - wszystkie muszą się powieść

# %% Tests
"""
>>> import sys; sys.tracebacklimit = 0
>>> assert sys.version_info >= (3, 9), \
'Python 3.9+ required'

>>> assert result is not Ellipsis, \
'Assign your result to variable `result`'
>>> assert type(result) is list, \
'Variable `result` has invalid type, should be list'
>>> assert len(result) == 3, \
'Variable `result` length should be 3'

>>> assert (1, 2, 3) in result
>>> assert [1.1, 2.2, 3.3] in result
>>> assert {'red', 'green', 'blue'} in result
"""

# Result should contain:
# - tuple: 1, 2, 3
# - list: 1.1, 2.2, 3.3
# - set: 'red', 'green', 'blue'
# type: list[tuple|list|set]
result = ...