14.3. Comprehension Slice

14.3.1. Recap

>>> DATA = [
...     ('firstname', 'lastname', 'age'),
...     ('Alice', 'Apricot', 30),
...     ('Bob', 'Blackthorn', 31),
...     ('Carol', 'Corn', 32),
...     ('Dave', 'Durian', 33),
...     ('Eve', 'Elderberry', 34),
...     ('Mallory', 'Melon', 15),
... ]
>>>
>>> [row for row in DATA]
[('firstname', 'lastname', 'age'),
 ('Alice', 'Apricot', 30),
 ('Bob', 'Blackthorn', 31),
 ('Carol', 'Corn', 32),
 ('Dave', 'Durian', 33),
 ('Eve', 'Elderberry', 34),
 ('Mallory', 'Melon', 15)]

14.3.2. Skip Header

>>> DATA = [
...     ('firstname', 'lastname', 'age'),
...     ('Alice', 'Apricot', 30),
...     ('Bob', 'Blackthorn', 31),
...     ('Carol', 'Corn', 32),
...     ('Dave', 'Durian', 33),
...     ('Eve', 'Elderberry', 34),
...     ('Mallory', 'Melon', 15),
... ]
>>>
>>> [row for row in DATA[1:]]
[('Alice', 'Apricot', 30),
 ('Bob', 'Blackthorn', 31),
 ('Carol', 'Corn', 32),
 ('Dave', 'Durian', 33),
 ('Eve', 'Elderberry', 34),
 ('Mallory', 'Melon', 15)]

14.3.3. Select Column

>>> DATA = [
...     ('firstname', 'lastname', 'age'),
...     ('Alice', 'Apricot', 30),
...     ('Bob', 'Blackthorn', 31),
...     ('Carol', 'Corn', 32),
...     ('Dave', 'Durian', 33),
...     ('Eve', 'Elderberry', 34),
...     ('Mallory', 'Melon', 15),
... ]
>>>
>>> [row[0] for row in DATA[1:]]
['Alice', 'Bob', 'Carol', 'Dave', 'Eve', 'Mallory']
>>>
>>> [row[1] for row in DATA[1:]]
['Apricot', 'Blackthorn', 'Corn', 'Durian', 'Elderberry', 'Melon']
>>>
>>> [row[2] for row in DATA[1:]]
[30, 31, 32, 33, 34, 15]

14.3.4. Select Multiple Columns

>>> DATA = [
...     ('firstname', 'lastname', 'age'),
...     ('Alice', 'Apricot', 30),
...     ('Bob', 'Blackthorn', 31),
...     ('Carol', 'Corn', 32),
...     ('Dave', 'Durian', 33),
...     ('Eve', 'Elderberry', 34),
...     ('Mallory', 'Melon', 15),
... ]
>>>
>>>
>>> [row[0:2] for row in DATA[1:]]
[('Alice', 'Apricot'),
 ('Bob', 'Blackthorn'),
 ('Carol', 'Corn'),
 ('Dave', 'Durian'),
 ('Eve', 'Elderberry'),
 ('Mallory', 'Melon')]
>>>
>>> [row[:-1] for row in DATA[1:]]
[('Alice', 'Apricot'),
 ('Bob', 'Blackthorn'),
 ('Carol', 'Corn'),
 ('Dave', 'Durian'),
 ('Eve', 'Elderberry'),
 ('Mallory', 'Melon')]

14.3.5. Unpack Sequences

>>> DATA = [
...     ('firstname', 'lastname', 'age'),
...     ('Alice', 'Apricot', 30),
...     ('Bob', 'Blackthorn', 31),
...     ('Carol', 'Corn', 32),
...     ('Dave', 'Durian', 33),
...     ('Eve', 'Elderberry', 34),
...     ('Mallory', 'Melon', 15),
... ]
>>>
>>> [(fn,ln) for fn,ln,age in DATA[1:]]
[('Alice', 'Apricot'),
 ('Bob', 'Blackthorn'),
 ('Carol', 'Corn'),
 ('Dave', 'Durian'),
 ('Eve', 'Elderberry'),
 ('Mallory', 'Melon')]

14.3.6. Use Case - 1

• Unique

>>> DATA = [
...     ('sepal_length', 'sepal_width', 'petal_length', 'petal_width', 'species'),
...     (5.8, 2.7, 5.1, 1.9, 'virginica'),
...     (5.1, 3.5, 1.4, 0.2, 'setosa'),
...     (5.7, 2.8, 4.1, 1.3, 'versicolor'),
...     (6.3, 2.9, 5.6, 1.8, 'virginica'),
...     (6.4, 3.2, 4.5, 1.5, 'versicolor'),
...     (4.7, 3.2, 1.3, 0.2, 'setosa'),
...     (7.0, 3.2, 4.7, 1.4, 'versicolor'),
... ]

>>> result = {species for sl,sw,pl,pw,species in DATA[1:]}
>>>
>>> sorted(result)
['setosa', 'versicolor', 'virginica']

14.3.7. Assignments

# %% About
# - Name: Comprehension Slice List of Dicts
# - Difficulty: easy
# - Lines: 2
# - 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. Select values in column `age`
# 2. Use comprehension
# 3. Run doctests - all must succeed

# %% Polish
# 1. Wybierz wartości w kolumnie `age`
# 2. Użyj comprehensions
# 3. Uruchom doctesty - wszystkie muszą się powieść

# %% Expected
# >>> result
# [30, 31, 32, 33, 34, 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 '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`.'

>>> result
[30, 31, 32, 33, 34, 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
result: list[int]

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

# %% Result
result = ...

# %% About
# - Name: Comprehension Slice List of Tuples
# - Difficulty: easy
# - Lines: 2
# - 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. Select values in column `age`
# 2. Use comprehension
# 3. Run doctests - all must succeed

# %% Polish
# 1. Wybierz wartości w kolumnie `age`
# 2. Użyj comprehensions
# 3. Uruchom doctesty - wszystkie muszą się powieść

# %% Expected
# >>> result
# [30, 31, 32, 33, 34, 15]

# %% Hints

# %% 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 list, \
'Variable `result` has an invalid type; expected: `list`.'

>>> result
[30, 31, 32, 33, 34, 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
result: list[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: Comprehension Slice List of Tuples
# - Difficulty: easy
# - Lines: 2
# - 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. Select values in column `firstname` and `lastname`
# 2. Use comprehension
# 3. Run doctests - all must succeed

# %% Polish
# 1. Wybierz wartości w kolumnie `firstname` i `lastname`
# 2. Użyj comprehensions
# 3. Uruchom doctesty - wszystkie muszą się powieść

# %% Expected
# >>> result
# [('Alice', 'Apricot'), ('Bob', 'Blackthorn'), ('Carol', 'Corn'), ('Dave', 'Durian'), ('Eve', 'Elderberry'), ('Mallory', 'Melon')]

# %% Hints

# %% 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 list, \
'Variable `result` has an invalid type; expected: `list`.'

>>> result
[('Alice', 'Apricot'), ('Bob', 'Blackthorn'), ('Carol', 'Corn'), ('Dave', 'Durian'), ('Eve', 'Elderberry'), ('Mallory', 'Melon')]
"""

# %% 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: list[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 = ...