10.1. Unpack Getitem

• Get item from ordered sequence

• Works with ordered sequences: str, list, tuple

• Index must be int (positive, negative or zero)

• Positive Index starts with 0

• Negative index starts with -1

>>> data = ['Alice', 'Bob', 'Carol']
>>>
>>> data[0]
'Alice'

10.1.1. Positive Index

• Ascending order

• Index must be less than length of an object

• If index does not exist, then IndexError exception will be raised

SetUp:

>>> data = ['Alice', 'Bob', 'Carol']

You can ask iterable about element at index, mind that Python starts indexing from 0:

>>> data[0]
'Alice'
>>>
>>> data[1]
'Bob'
>>>
>>> data[2]
'Carol'

Index must be less than length of an object. If index does not exist, then IndexError exception will be raised:

>>> data[3]
Traceback (most recent call last):
IndexError: list index out of range

10.1.2. Negative Index

• Descending order

• Starts with -1

• Number 0 is equal to -0

• Negative index starts from the end and go right to left

SetUp:

>>> data = ['Alice', 'Bob', 'Carol']

Negative index starts from the end and go right to left:

>>> data[-1]
'Carol'
>>>
>>> data[-2]
'Bob'
>>>
>>> data[-3]
'Alice'

Number 0 is equal to -0:

>>> data[-0]
'Alice'
>>>
>>> -0 == 0
True

Index must be less than length of an object. If index does not exist, then IndexError exception will be raised:

>>> data[-4]
Traceback (most recent call last):
IndexError: list index out of range

10.1.3. Index Type

• Index must int (positive, negative or zero)

SetUp:

>>> data = ['Alice', 'Bob', 'Carol']

Index must int (positive, negative or zero):

>>> data[0]
'Alice'
>>>
>>> data[1]
'Bob'
>>>
>>> data[-1]
'Carol'

Any other type, even float or str, will not work:

>>> data[1.0]
Traceback (most recent call last):
TypeError: list indices must be integers or slices, not float
>>>
>>> data['one']
Traceback (most recent call last):
TypeError: list indices must be integers or slices, not str

10.1.4. Getitem from str

Get Item from str:

>>> data = 'Alice'

Positive index:

>>> data[1]
'l'
>>>
>>> data[2]
'i'

Zero index:

>>> data[0]
'A'
>>>
>>> data[-0]
'A'

Negative index:

>>> data[-1]
'e'
>>>
>>> data[-2]
'c'

10.1.5. Getitem from list

Getitem from list:

>>> data = ['Alice', 'Bob', 'Carol']

Positive index:

>>> data[1]
'Bob'
>>>
>>> data[2]
'Carol'

Zero index:

>>> data[0]
'Alice'
>>>
>>> data[-0]
'Alice'

Negative index:

>>> data[-1]
'Carol'
>>>
>>> data[-2]
'Bob'
>>>
>>> data[-3]
'Alice'

10.1.6. Getitem from tuple

Getitem from tuple:

>>> data = ('Alice', 'Bob', 'Carol')

Positive index:

>>> data[1]
'Bob'
>>>
>>> data[2]
'Carol'

Zero index:

>>> data[0]
'Alice'
>>>
>>> data[-0]
'Alice'

Negative index:

>>> data[-1]
'Carol'
>>>
>>> data[-2]
'Bob'
>>>
>>> data[-3]
'Alice'

10.1.7. Getitem from set

Getitem from set is impossible. set is unordered data structure:

>>> data = {'Alice', 'Bob', 'Carol'}

Positive index:

>>> data[1]
Traceback (most recent call last):
TypeError: 'set' object is not subscriptable
>>>
>>> data[2]
Traceback (most recent call last):
TypeError: 'set' object is not subscriptable

Zero index:

>>> data[0]
Traceback (most recent call last):
TypeError: 'set' object is not subscriptable
>>>
>>> data[-0]
Traceback (most recent call last):
TypeError: 'set' object is not subscriptable

Negative index:

>>> data[-1]
Traceback (most recent call last):
TypeError: 'set' object is not subscriptable
>>>
>>> data[-2]
Traceback (most recent call last):
TypeError: 'set' object is not subscriptable

10.1.8. Getitem from dict

• Getitem with index on dict is not possible

Non-integer keys:

>>> data = {'Alice': 0, 'Bob': 1, 'Carol': 2}
>>>
>>>
>>> data['Alice']
0
>>>
>>> data[0]
Traceback (most recent call last):
KeyError: 0

Integer keys:

>>> data = {0: 'Alice', 1: 'Bob', 2: 'Carol'}
>>>
>>>
>>> data['Alice']
Traceback (most recent call last):
KeyError: 'Alice'
>>>
>>> data[0]
'Alice'
>>>
>>> data[-1]
Traceback (most recent call last):
KeyError: -1

10.1.9. Getitem from list[list]

Get elements from list of list:

>>> data = [
...     [1, 2, 3],
...     [4, 5, 6],
...     [7, 8, 9],
... ]
>>>
>>> data[0]
[1, 2, 3]
>>>
>>> data[0][1]
2

10.1.10. Getitem from list[tuple]

Get elements from list of tuple:

>>> data = [
...     ('Alice', 'Apricot'),
...     ('Bob', 'Blackthorn'),
...     ('Carol', 'Corn'),
... ]
>>>
>>> data[0]
('Alice', 'Apricot')
>>>
>>> data[0][0]
'Alice'
>>>
>>> data[0][0][0]
'A'

10.1.11. Getitem from list[dict]

>>> data = [
...     {'firstname': 'Alice', 'lastname': 'Apricot'},
...     {'firstname': 'Bob', 'lastname': 'Blackthorn'},
...     {'firstname': 'Carol', 'lastname': 'Corn'},
... ]
>>>
>>>
>>> data[0]
{'firstname': 'Alice', 'lastname': 'Apricot'}
>>>
>>> data[0]['firstname']
'Alice'
>>>
>>> data[0]['firstname'][0]
'A'

10.1.12. Getitem from list[Sequence]

• list of mixed Sequence, such as: list, tuple or str

Get elements from list of sequences:

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

List:

>>> data[0]
[1, 2, 3]
>>>
>>> data[0][1]
2

Tuple:

>>> data[1]
(4, 5, 6)
>>>
>>> data[1][0]
4

Set:

>>> data[2]
{8, 9, 7}
>>>
>>> data[2][0]
Traceback (most recent call last):
TypeError: 'set' object is not subscriptable

10.1.13. Use Case - 1

>>> ranking = {
...    0: 'Alice',
...    1: 'Bob',
...    2: 'Carol',
... }
>>>
>>>
>>> ranking[0]
'Alice'
>>>
>>> ranking[1]
'Bob'
>>>
>>> ranking[2]
'Carol'
>>>
>>> ranking[-0]
'Alice'
>>>
>>> ranking[-1]
Traceback (most recent call last):
KeyError: -1

10.1.14. Use Case - 2

>>> calendarium = {
...    1961: 'First Human Space Flight',
...    1969: 'First Step on the Moon',
... }
>>>
>>>
>>> calendarium[1961]
'First Human Space Flight'
>>>
>>> calendarium['1961']
Traceback (most recent call last):
KeyError: '1961'

10.1.15. Recap

• Get item from ordered sequence

• Works with ordered sequences: str, list, tuple

• Index must be int (positive, negative or zero)

• Positive Index starts with 0

• Negative index starts with -1

>>> data = ['Alice', 'Bob', 'Carol']
>>>
>>> data[0]
'Alice'
>>>
>>> data[-1]
'Carol'

10.1.16. Assignments

# %% About
# - Name: Unpack Getitem Header
# - Difficulty: easy
# - Lines: 1
# - Minutes: 2

# %% 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

# %% English
# 1. Define `result: tuple` with `DATA` header (row with index 0)
# 2. Use getitem, i.e.: `list[index]`
# 3. Run doctests - all must succeed

# %% Polish
# 1. Zdefiniuj `result: tuple` z nagłówkiem `DATA` (wiersz o indeksie 0)
# 2. Użyj getitem, tj. `list[index]`
# 3. Uruchom doctesty - wszystkie muszą się powieść

# %% Expected
# >>> result
# ('firstname', 'lastname', 'age')

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0

>>> assert sys.version_info >= (3, 9), \
'Python has an is invalid version; expected: `3.9` or newer.'

>>> assert 'result' in globals(), \
'Variable `result` is not defined; assign result of your program to it.'

>>> assert result is not Ellipsis, \
'Variable `result` has an invalid value; assign result of your program to it.'

>>> assert type(result) is tuple, \
'Variable `result` has an invalid type; expected: `tuple`.'

>>> assert len(result) == 3, \
'Variable `result` has an invalid length; expected: `3`.'

>>> result
('firstname', 'lastname', 'age')
"""

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

# %% Imports

# %% Types
result: tuple[str,str,str] | tuple[str,str,int]

# %% Data
DATA = [
    ('firstname', 'lastname', 'age'),
    ('Alice', 'Apricot', 30),
    ('Bob', 'Blackthorn', 31),
    ('Carol', 'Corn', 32),
    ('Dave', 'Durian', 33),
    ('Eve', 'Elderberry', 34),
    ('Mallory', 'Melon', 15),
]

# %% Result
result = ...

# %% About
# - Name: Unpack Getitem Positive
# - Difficulty: easy
# - Lines: 3
# - Minutes: 2

# %% 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

# %% English
# 1. Define `result1: tuple` with row from `DATA` at index 2
# 2. Define `result2: tuple` with row from `DATA` at index 4
# 3. Define `result3: tuple` with row from `DATA` at index 6
# 4. Use getitem, i.e.: `list[index]`
# 5. Run doctests - all must succeed

# %% Polish
# 1. Zdefiniuj `result1: tuple` z wierszem z `DATA` o indeksie 2
# 2. Zdefiniuj `result2: tuple` z wierszem z `DATA` o indeksie 4
# 3. Zdefiniuj `result3: tuple` z wierszem z `DATA` o indeksie 6
# 4. Użyj getitem, tj. `list[index]`
# 5. Uruchom doctesty - wszystkie muszą się powieść

# %% Expected
# >>> result1
# ('Bob', 'Blackthorn', 31)
#
# >>> result2
# ('Dave', 'Durian', 33)
#
# >>> result3
# ('Mallory', 'Melon', 15)

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0

>>> assert sys.version_info >= (3, 9), \
'Python has an is invalid version; expected: `3.9` or newer.'

>>> assert 'result1' in globals(), \
'Variable `result1` is not defined; assign result of your program to it.'

>>> assert result1 is not Ellipsis, \
'Variable `result1` has an invalid value; assign result of your program to it.'

>>> assert type(result1) is tuple, \
'Variable `result1` has an invalid type; expected: `tuple`.'

>>> assert len(result1) == 3, \
'Variable `result1` has an invalid length; expected: `3`.'

>>> assert 'result2' in globals(), \
'Variable `result2` is not defined; assign result of your program to it.'

>>> assert result2 is not Ellipsis, \
'Variable `result2` has an invalid value; assign result of your program to it.'

>>> assert type(result2) is tuple, \
'Variable `result2` has an invalid type; expected: `tuple`.'

>>> assert len(result2) == 3, \
'Variable `result2` has an invalid length; expected: `3`.'

>>> assert 'result3' in globals(), \
'Variable `result3` is not defined; assign result of your program to it.'

>>> assert result3 is not Ellipsis, \
'Variable `result3` has an invalid value; assign result of your program to it.'

>>> assert type(result3) is tuple, \
'Variable `result3` has an invalid type; expected: `tuple`.'

>>> assert len(result3) == 3, \
'Variable `result3` has an invalid length; expected: `3`.'

>>> result1
('Bob', 'Blackthorn', 31)

>>> result2
('Dave', 'Durian', 33)

>>> result3
('Mallory', 'Melon', 15)
"""

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

# %% Imports

# %% Types
result1: tuple[str, str, str] | tuple[str,str,int]
result2: tuple[str, str, str] | tuple[str,str,int]
result3: tuple[str, str, str] | tuple[str,str,int]

# %% Data
DATA = [
    ('firstname', 'lastname', 'age'),
    ('Alice', 'Apricot', 30),
    ('Bob', 'Blackthorn', 31),
    ('Carol', 'Corn', 32),
    ('Dave', 'Durian', 33),
    ('Eve', 'Elderberry', 34),
    ('Mallory', 'Melon', 15),
]

# %% Result
result1 = ...
result2 = ...
result3 = ...

# %% About
# - Name: Unpack Getitem Negative
# - Difficulty: easy
# - Lines: 3
# - Minutes: 2

# %% 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

# %% English
# 1. Define `result1: tuple` with row from `DATA` at index -1
# 2. Define `result2: tuple` with row from `DATA` at index -3
# 3. Define `result3: tuple` with row from `DATA` at index -5
# 4. Use getitem, i.e.: `list[index]`
# 5. Run doctests - all must succeed

# %% Polish
# 1. Zdefiniuj `result1: tuple` z wierszem z `DATA` o indeksie -1
# 2. Zdefiniuj `result2: tuple` z wierszem z `DATA` o indeksie -3
# 3. Zdefiniuj `result3: tuple` z wierszem z `DATA` o indeksie -5
# 4. Użyj getitem, tj. `list[index]`
# 5. Uruchom doctesty - wszystkie muszą się powieść

# %% Expected
# >>> result1
# ('Mallory', 'Melon', 15)
#
# >>> result2
# ('Dave', 'Durian', 33)
#
# >>> result3
# ('Bob', 'Blackthorn', 31)

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0

>>> assert sys.version_info >= (3, 9), \
'Python has an is invalid version; expected: `3.9` or newer.'

>>> assert 'result1' in globals(), \
'Variable `result1` is not defined; assign result of your program to it.'

>>> assert result1 is not Ellipsis, \
'Variable `result1` has an invalid value; assign result of your program to it.'

>>> assert type(result1) is tuple, \
'Variable `result1` has an invalid type; expected: `tuple`.'

>>> assert len(result1) == 3, \
'Variable `result1` has an invalid length; expected: `3`.'

>>> assert 'result2' in globals(), \
'Variable `result2` is not defined; assign result of your program to it.'

>>> assert result2 is not Ellipsis, \
'Variable `result2` has an invalid value; assign result of your program to it.'

>>> assert type(result2) is tuple, \
'Variable `result2` has an invalid type; expected: `tuple`.'

>>> assert len(result2) == 3, \
'Variable `result2` has an invalid length; expected: `3`.'

>>> assert 'result3' in globals(), \
'Variable `result3` is not defined; assign result of your program to it.'

>>> assert result3 is not Ellipsis, \
'Variable `result3` has an invalid value; assign result of your program to it.'

>>> assert type(result3) is tuple, \
'Variable `result3` has an invalid type; expected: `tuple`.'

>>> assert len(result3) == 3, \
'Variable `result3` has an invalid length; expected: `3`.'

>>> result1
('Mallory', 'Melon', 15)

>>> result2
('Dave', 'Durian', 33)

>>> result3
('Bob', 'Blackthorn', 31)
"""

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

# %% Imports

# %% Types
result1: tuple[str,str,int]
result2: tuple[str,str,int]
result3: tuple[str,str,int]

# %% Data
DATA = [
    ('firstname', 'lastname', 'age'),
    ('Alice', 'Apricot', 30),
    ('Bob', 'Blackthorn', 31),
    ('Carol', 'Corn', 32),
    ('Dave', 'Durian', 33),
    ('Eve', 'Elderberry', 34),
    ('Mallory', 'Melon', 15),
]

# %% Result
result1 = ...
result2 = ...
result3 = ...

# %% About
# - Name: Unpack Getitem Select
# - Difficulty: easy
# - Lines: 4
# - Minutes: 3

# %% 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

# %% English
# 1. Define `result: list` with rows from `DATA` at indexes: 0, 1, -1
# 2. Use getitem, i.e.: `list[index]`
# 3. Run doctests - all must succeed

# %% Polish
# 1. Zdefiniuj `result: list` z wierszami z `DATA` o indeksach: 0, 1, -1
# 2. Użyj getitem, tj. `list[index]`
# 3. Uruchom doctesty - wszystkie muszą się powieść

# %% Expected
# >>> result
# [('firstname', 'lastname', 'age'),
#  ('Alice', 'Apricot', 30),
#  ('Mallory', 'Melon', 15)]

# %% Hints
# - `list.append()`

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0

>>> assert sys.version_info >= (3, 12), \
'Python has an is invalid version; expected: `3.12` or newer.'

>>> from pprint import pprint

>>> assert 'result' in globals(), \
'Variable `result` is not defined; assign result of your program to it.'

>>> assert result is not Ellipsis, \
'Variable `result` has an invalid value; assign result of your program to it.'

>>> assert type(result) is list, \
'Variable `result` has an invalid type; expected: `list`.'

>>> assert len(result) == 3, \
'Variable `result` has an invalid length; expected: `3`.'

>>> pprint(result)
[('firstname', 'lastname', 'age'),
 ('Alice', 'Apricot', 30),
 ('Mallory', 'Melon', 15)]
"""

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

# %% Imports

# %% Types
type header = tuple[str,str,str]
type row = tuple[str,str,int]
result: list[header|row]

# %% Data
DATA = [
    ('firstname', 'lastname', 'age'),
    ('Alice', 'Apricot', 30),
    ('Bob', 'Blackthorn', 31),
    ('Carol', 'Corn', 32),
    ('Dave', 'Durian', 33),
    ('Eve', 'Elderberry', 34),
    ('Mallory', 'Melon', 15),
]

# %% Result
result = ...

# %% About
# - Name: Unpack Getitem Header/Data
# - Difficulty: easy
# - Lines: 11
# - Minutes: 3

# %% 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

# %% English
# 1. Define `header: tuple[str]` with a header (first line of `DATA`)
# 2. Define `rows: list[tuple]` with rows (all the other lines of `DATA`)
# 3. Use getitem, i.e.: `list[index]`
# 4. Do not use slice, i.e.: `list[start:stop:step]`
# 5. Run doctests - all must succeed

# %% Polish
# 1. Zdefiniuj `header: tuple[str]` z nagłówkiem (pierwsza linia `DATA`)
# 2. Zdefiniuj `rows: list[tuple]` z wierszami (wszystkie inne linie `DATA`)
# 3. Użyj getitem, tj. `list[index]`
# 4. Nie używaj slice, tj. `list[start:stop:step]`
# 5. Uruchom doctesty - wszystkie muszą się powieść

# %% Expected
# >>> header
# ('firstname', 'lastname', 'age')
#
# >>> rows
# [('Alice', 'Apricot', 30),
#  ('Bob', 'Blackthorn', 31),
#  ('Carol', 'Corn', 32),
#  ('Dave', 'Durian', 33),
#  ('Eve', 'Elderberry', 34),
#  ('Mallory', 'Melon', 15)]

# %% Hints
# - `list.append()`

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0

>>> assert sys.version_info >= (3, 9), \
'Python has an is invalid version; expected: `3.9` or newer.'

>>> from pprint import pprint

>>> assert header is not Ellipsis, \
'Variable `header` has an invalid value; assign result of your program to it.'

>>> assert type(header) is tuple, \
'Variable `header` has an invalid type; expected: `tuple`.'

>>> assert header not in rows, \
'Header should not be in `rows`'

>>> assert rows is not Ellipsis, \
'Variable `rows` has an invalid value; assign result of your program to it.'

>>> assert all(type(x) is tuple for x in rows), \
'Variable `rows` has elements of an invalid type; all items should be: `tuple`.'

>>> content = open(__file__).read()
>>> assert 'DATA'+'[1:]' not in content, \
'Slice `list[start:stop:step]` was used; expected: use getitem `list[index]`.'

>>> assert 'DATA'+'[1:11]' not in content, \
'Slice `list[start:stop:step]` was used; expected: use getitem `list[index]`.'

>>> pprint(header)
('firstname', 'lastname', 'age')

>>> pprint(rows)
[('Alice', 'Apricot', 30),
 ('Bob', 'Blackthorn', 31),
 ('Carol', 'Corn', 32),
 ('Dave', 'Durian', 33),
 ('Eve', 'Elderberry', 34),
 ('Mallory', 'Melon', 15)]
"""

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

# %% Imports

# %% Types
header = tuple[str,str,str]
rows = list[tuple[str,str,int]]

# %% Data
DATA = [
    ('firstname', 'lastname', 'age'),
    ('Alice', 'Apricot', 30),
    ('Bob', 'Blackthorn', 31),
    ('Carol', 'Corn', 32),
    ('Dave', 'Durian', 33),
    ('Eve', 'Elderberry', 34),
    ('Mallory', 'Melon', 15),
]

# %% Result
header = ...
rows = ...