7.4. Loop Unpacking Assignment¶
7.4.1. Recap¶
>>> a, b = 1, 2
>>> a, b = (1, 2)
>>> k, v = (1, 2)
>>> key, value = (1, 2)
>>> role, name = ('commander', 'Melissa Lewis')
7.4.2. List of Pairs¶
>>> DATA = [('commander', 'Melissa Lewis'),
... ('botanist', 'Mark Watney'),
... ('chemist', 'Alex Vogel')]
>>>
>>> for role, name in DATA:
... print(f'{role} -> {name}')
commander -> Melissa Lewis
botanist -> Mark Watney
chemist -> Alex Vogel
7.4.3. List of Tuples¶
>>> DATA = [(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')]
>>>
>>> for sepal_length, sepal_width, petal_length, petal_width, species in DATA:
... print(f'{species} -> {sepal_length}')
setosa -> 5.1
versicolor -> 5.7
virginica -> 6.3
>>> DATA = [(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')]
>>>
>>> for sl, sw, pl, pw, s in DATA:
... print(f'{s} -> {sl}')
setosa -> 5.1
versicolor -> 5.7
virginica -> 6.3
7.4.4. Unpacking Assignment¶
>>> *features, label = (5.8, 2.7, 5.1, 1.9, 'virginica')
>>>
>>> features
[5.8, 2.7, 5.1, 1.9]
>>> label
'virginica'
>>> DATA = [(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')]
>>>
>>> for *features, label in DATA:
... avg = sum(features) / len(features)
... print(f'{label} -> {avg}')
virginica -> 3.875
setosa -> 2.55
versicolor -> 3.475
>>> DATA = [(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')]
>>>
>>> for *X,y in DATA:
... avg = sum(X) / len(X)
... print(f'{y} -> {avg}')
virginica -> 3.875
setosa -> 2.55
versicolor -> 3.475
7.4.5. Unused Values¶
>>> DATA = [(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')]
>>>
>>> for sepal_length, _, _, _, species in DATA:
... print(f'{species} -> {sepal_length}')
setosa -> 5.1
versicolor -> 5.7
virginica -> 6.3
>>> DATA = [(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')]
>>>
>>> for sepal_length, *_, species in DATA:
... print(f'{species} -> {sepal_length}')
virginica -> 5.8
setosa -> 5.1
versicolor -> 5.7
7.4.6. Mixed¶
>>> DATA = [(1, 2),
... ('name', 'Jan Twardowski'),
... ('species', ['setosa', 'versicolor', 'virginica']),
... ((1, 2), ['Johnson Space Center', 'Kennedy Space Center']),
... (['NASA', 'ESA', 'Roscosmos'], 1)]
>>>
>>> for first, second in DATA:
... print(f'{first} -> {second}')
1 -> 2
name -> Jan Twardowski
species -> ['setosa', 'versicolor', 'virginica']
(1, 2) -> ['Johnson Space Center', 'Kennedy Space Center']
['NASA', 'ESA', 'Roscosmos'] -> 1
7.4.7. Enumerate¶
Pythonic way
Preferred over
i=0andi+=1for every iterationenumerate()will returncounterandvaluefor every iteration
>>> DATA = ['a', 'b', 'c']
>>> result = enumerate(DATA)
>>>
>>> next(result)
(0, 'a')
>>> next(result)
(1, 'b')
>>> next(result)
(2, 'c')
>>> next(result)
Traceback (most recent call last):
StopIteration
enumerate() will return counter and value for every iteration:
>>> DATA = ['a', 'b', 'c']
>>>
>>> for i, letter in enumerate(DATA):
... print(f'{i} -> {letter}')
0 -> a
1 -> b
2 -> c
enumerate() can start with custom number:
>>> DATA = ['a', 'b', 'c']
>>>
>>> for i, letter in enumerate(DATA, start=5):
... print(f'{i} -> {letter}')
5 -> a
6 -> b
7 -> c
>>> DATA = [(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')]
>>>
>>> for i, row in enumerate(DATA):
... print(f'{i} -> {row}')
0 -> (5.1, 3.5, 1.4, 0.2, 'setosa')
1 -> (5.7, 2.8, 4.1, 1.3, 'versicolor')
2 -> (6.3, 2.9, 5.6, 1.8, 'virginica')
7.4.8. Zip¶
>>> roles = ['commander', 'botanist', 'chemist']
>>> crew = ['Melissa Lewis', 'Mark Watney', 'Alex Vogel']
>>> result = zip(roles, crew)
>>>
>>> next(result)
('commander', 'Melissa Lewis')
>>> next(result)
('botanist', 'Mark Watney')
>>> next(result)
('chemist', 'Alex Vogel')
>>> next(result)
Traceback (most recent call last):
StopIteration
>>> roles = ['commander', 'botanist', 'chemist']
>>> crew = ['Melissa Lewis', 'Mark Watney', 'Alex Vogel']
>>>
>>> for role, name in zip(roles, crew):
... print(f'{role} -> {name}')
commander -> Melissa Lewis
botanist -> Mark Watney
chemist -> Alex Vogel
7.4.9. Assignments¶
"""
* Assignment: Loop Unpacking Months
* Complexity: easy
* Lines of code: 2 lines
* Time: 5 min
English:
1. Use data from "Given" section (see below)
2. Use `enumerate()` to convert `MONTH` into dict:
a. Keys: month number
b. Values: month name
3. Compare result with "Tests" section (see below)
Polish:
1. Użyj danych z sekcji "Given" (patrz poniżej)
2. Użyj `enumerate()` do konwersji `MONTH` w słownik:
a. klucz: numer miesiąca
b. wartość: nazwa miesiąca
3. Porównaj wyniki z sekcją "Tests" (patrz poniżej)
Tests:
>>> import sys
>>> sys.tracebacklimit = 0
>>> type(result)
<class 'dict'>
>>> assert all(type(x) is int for x in result.keys())
>>> assert all(type(x) is str for x in result.values())
>>> assert all(x in result.keys() for x in range(1, 13))
>>> assert all(x in result.values() for x in MONTHS)
>>> 13 not in result
True
>>> 0 not in result
True
>>> result # doctest: +NORMALIZE_WHITESPACE
{1: 'January',
2: 'February',
3: 'March',
4: 'April',
5: 'May',
6: 'June',
7: 'July',
8: 'August',
9: 'September',
10: 'October',
11: 'November',
12: 'December'}
"""
# Given
MONTHS = [
'January',
'February',
'March',
'April',
'May',
'June',
'July',
'August',
'September',
'October',
'November',
'December',
]
result = ... # dict[int,str]: dict with month number and name. Start with 1
"""
* Assignment: Loop Unpacking Endswith
* Complexity: medium
* Lines of code: 4 lines
* Time: 13 min
English:
1. Use data from "Given" section (see below)
2. Define `result: set[str]`
3. Iterating over data unpack row to `*features` and `label`
4. Append to `result` species with endings in `SUFFIXES`
5. Compare result with "Tests" section (see below)
Polish:
1. Użyj danych z sekcji "Given" (patrz poniżej)
2. Zdefiniuj `result: set[str]`
3. Iterując po danych rozpakuj wiersz do `*features` oraz `label`
4. Dodaj do `result` nazwy gatunków z końcówkami w `SUFFIXES`
5. Porównaj wyniki z sekcją "Tests" (patrz poniżej)
Hints:
* `str.endswith()`
* `set.pop()`
Tests:
>>> type(result)
<class 'set'>
>>> 'virginica' in result
True
>>> 'setosa' in result
True
>>> 'versicolor' in result
False
"""
# Given
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'}),
(7.6, 3.0, 6.6, 2.1, {'virginica'}),
(4.6, 3.1, 1.5, 0.2, {'setosa'}),
]
SUFFIXES = ('ca', 'osa')
features: tuple
label: set
species: str
result = ... # set[str]: species names ending with 'ca' or 'osa'