Should We Return to Python 2?

No.

Transcript

1. Should We Return to Python 2? Miroslav Šedivý   eumiro 1
2. NO.   eumiro 2
3. NO.   eumiro 2
4.   eumiro 3
5. You have migrated your project to Python 3   eumiro 4
6. Which Python version to support? | | | | | | | | | 2.7 ============| | | | | | | | 3.4 === | | | | | | | | 3.5 ===================== | | | | | | | 3.6 ====================================| | | | | | 3.7 ##################==================================== | | | | 3.8 | ##################========================================== | | | 3.9 | | ####################========================================= | | 3.10 | | | ####################========================================= | 3.11 | | | | ####################========================================= 3.12 | | | | | ####################=============================→ 3.13 | | | | | | ####################=================→ π-py | | | | | | | ####################=====→ 3.15 | | | | | | | | #############→ | | | | | | | | | +-----------+-----------+--X--------+-----------+-----------+-----------+-----------+-----------+---- 2019 2020 2021 2022 2023 2024 2025 2026 2027   eumiro 5
7. Which Python version to support? | | | | | | | | | 2.7 ============| | | | | | | | 3.4 === | | | | | | | | 3.5 ===================== | | | | | | | 3.6 ====================================| | | | | | 3.7 ##################==================================== | | | | 3.8 | ##################========================================== | | | 3.9 | | ####################========================================= | | 3.10 | | | ####################========================================= | 3.11 | | | | ####################========================================= 3.12 | | | | | ####################=============================→ 3.13 | | | | | | ####################=================→ π-py | | | | | | | ####################=====→ 3.15 | | | | | | | | #############→ | | | | | | | | | +-----------+-----------+--X--------+-----------+-----------+-----------+-----------+-----------+---- 2019 2020 2021 2022 2023 2024 2025 2026 2027 an application: 3.9 a library: 3.6–3.9   eumiro 5
8. Your code runs in Python 3? print … d.iterkeys() d.itervalues() d.iteritems() xrange(…)   eumiro 6
9. Your code runs in Python 3? print … d.iterkeys() d.itervalues() d.iteritems() xrange(…) six if sys.version_info > (3, 0) try: import x except ImportError: import y   eumiro 6
10. Make sure it runs ├── .github │ └── workflows │ └── ci.yml ├── setup.py ├── src │ └── project │ └── … ├── tests │ └── … └── tox.ini   eumiro 7
11. Make sure it runs ├── .github │ └── workflows │ └── ci.yml ├── setup.py ├── src │ └── project │ └── … ├── tests │ └── … └── tox.ini [tox] envlist = py36,py37,py38,py39 [testenv] deps = pytest commands = python -m pytest {posargs}   eumiro 7
12. name: CI on: [push, pull_request] jobs: build: runs-on: ubuntu-latest strategy: matrix: python-version: [3.6, 3.7, 3.8, 3.9] steps: - uses: actions/checkout@v1 - name: Set up Python ${{ matrix.python-version }} uses: actions/setup-python@v2 with: python-version: ${{ matrix.python-version }} - name: Install dependencies run: | python -m pip install --upgrade pip pip install tox - name: Test with tox run: tox   eumiro 8
13. https://github.com/jugmac00/python-version-cheat-sheet python 3.6 introduction of type annotations for variables (PEP 526) f-strings (PEP 498) introduction of underscores in numeric literals, e.g. 1_000 (PEP 515) python 3.7 postponed evaluation of annotations via from __future__ import annotations (PEP 563) sort order of dicts is now guaranteed introduction of breakpoint, additionally to import pdb;pdb.set_trace() (PEP 553) introduction of data classes (PEP 557) python 3.8 introduction of the walrus operator (PEP 572) python 3.9 builtin generic types, that means you can use list and dict for type annotations, instead of importing e.g. from typing import List (PEP 585)   eumiro 9
14. # coding: utf-8 (utf-8 is default)   eumiro 10
15. # coding: utf-8 (utf-8 is default) class Dummy(object): class Dummy:   eumiro 10
16. # coding: utf-8 (utf-8 is default) class Dummy(object): class Dummy: super(Inherited, self).func() super().func()   eumiro 10
17. # coding: utf-8 (utf-8 is default) class Dummy(object): class Dummy: super(Inherited, self).func() super().func() u'hello world' "hello world"   eumiro 10
18. # coding: utf-8 (utf-8 is default) class Dummy(object): class Dummy: super(Inherited, self).func() super().func() u'hello world' "hello world" pip install pyupgrade   eumiro 10
19. # coding: utf-8 (utf-8 is default) class Dummy(object): class Dummy: super(Inherited, self).func() super().func() u'hello world' "hello world" pip install pyupgrade pyupgrade --py36-plus **/*.py   eumiro 10
20. # coding: utf-8 (utf-8 is default) class Dummy(object): class Dummy: super(Inherited, self).func() super().func() u'hello world' "hello world" pip install pyupgrade pyupgrade --py36-plus **/*.py Make sure it looks good: black/blue, yapf flake8, pylint   eumiro 10
21. String formatting 'Field %s contains value %r' % (field, value) 'Field {} contains value {!r}'.format(field, value) f'Field {field} contains value {value!r}'   eumiro 11
22. String formatting 'Field %s contains value %r' % (field, value) 'Field {} contains value {!r}'.format(field, value) f'Field {field} contains value {value!r}' log.info('Field %s contains value %r', field, value)   eumiro 11
23. String formatting 'Field %s contains value %r' % (field, value) 'Field {} contains value {!r}'.format(field, value) f'Field {field} contains value {value!r}' log.info('Field %s contains value %r', field, value) # -*- coding: latin-1 -*- func("���") func("\xef\xbf\xbd\xef\xbf\xbd\xef\xbf\xbd")   eumiro 11
24. String formatting 'Field %s contains value %r' % (field, value) 'Field {} contains value {!r}'.format(field, value) f'Field {field} contains value {value!r}' log.info('Field %s contains value %r', field, value) # -*- coding: latin-1 -*- func("���") func("\xef\xbf\xbd\xef\xbf\xbd\xef\xbf\xbd") "Šedivý" "\u0160ediv\00fd" "\N{LATIN CAPITAL LETTER S WITH CARON}ediv\N{LATIN SMALL LETTER Y WITH ACUTE}"   eumiro 11
25. Numbers int(math.floor(x)) int(math.ceil(x)) int(round(x))   eumiro 12
26. Numbers int(math.floor(x)) int(math.ceil(x)) int(round(x)) # Python 2 >>> sys.maxint 9_223_372_036_854_775_807 # Python 2+3 >>> sys.float_info.max 1.7976931348623157e+308   eumiro 12
27. >>> vals = [3, 3, 4, 4] >>> sum(vals) / len(vals) 3   eumiro 13
28. >>> vals = [3, 3, 4, 4] >>> sum(vals) / len(vals) 3 >>> float(sum(vals)) / len(vals) >>> sum(vals) / float(len(vals)) >>> 1.0 * sum(vals) / len(vals) 3.5   eumiro 13
29. >>> vals = [3, 3, 4, 4] >>> sum(vals) / len(vals) 3 >>> float(sum(vals)) / len(vals) >>> sum(vals) / float(len(vals)) >>> 1.0 * sum(vals) / len(vals) 3.5 >>> from __future__ import division >>> sum(vals) / len(vals) 3.5   eumiro 13
30. >>> vals = [3, 3, 4, 4] >>> sum(vals) / len(vals) 3 >>> float(sum(vals)) / len(vals) >>> sum(vals) / float(len(vals)) >>> 1.0 * sum(vals) / len(vals) 3.5 >>> from __future__ import division >>> sum(vals) / len(vals) 3.5 >>> sum(vals) / len(vals) 3.5   eumiro 13
31. “God made the integers; all else is the work of man.” — Leopold Kronecker   eumiro 14
32. “God made the integers; all else is the work of man.” — Leopold Kronecker >>> 9_007_199_254_740_993.0 9_007_199_254_740_992.0   eumiro 14
33. “God made the integers; all else is the work of man.” — Leopold Kronecker >>> 9_007_199_254_740_993.0 9_007_199_254_740_992.0 number of nanoseconds in 105 days   eumiro 14
34. “God made the integers; all else is the work of man.” — Leopold Kronecker >>> 9_007_199_254_740_993.0 9_007_199_254_740_992.0 number of nanoseconds in 105 days >>> 0.1 + 0.1 + 0.1 0.30000000000000004   eumiro 14
35. “God made the integers; all else is the work of man.” — Leopold Kronecker >>> 9_007_199_254_740_993.0 9_007_199_254_740_992.0 number of nanoseconds in 105 days >>> 0.1 + 0.1 + 0.1 0.30000000000000004 >>> sum(0.3 for _ in range(1_000_000)) # 50ms 299999.99999434233   eumiro 14
36. “God made the integers; all else is the work of man.” — Leopold Kronecker >>> 9_007_199_254_740_993.0 9_007_199_254_740_992.0 number of nanoseconds in 105 days >>> 0.1 + 0.1 + 0.1 0.30000000000000004 >>> sum(0.3 for _ in range(1_000_000)) # 50ms 299999.99999434233 >>> sum(decimal.Decimal('0.3') for _ in range(1_000_000)) # 350ms Decimal('300000.0')   eumiro 14
37. “God made the integers; all else is the work of man.” — Leopold Kronecker >>> 9_007_199_254_740_993.0 9_007_199_254_740_992.0 number of nanoseconds in 105 days >>> 0.1 + 0.1 + 0.1 0.30000000000000004 >>> sum(0.3 for _ in range(1_000_000)) # 50ms 299999.99999434233 >>> sum(decimal.Decimal('0.3') for _ in range(1_000_000)) # 350ms Decimal('300000.0') >>> sum(fractions.Fraction(3, 10) for _ in range(1_000_000)) # 3s Fraction(300000, 1)   eumiro 14
38. >>> hours = minutes / 60.0 hours = minutes / 60   eumiro 15
39. >>> hours = minutes / 60.0 hours = minutes / 60 >>> avg = (a + b) / 2.0 avg = (a + b) / 2   eumiro 15
40. >>> hours = minutes / 60.0 hours = minutes / 60 >>> avg = (a + b) / 2.0 avg = (a + b) / 2 >>> math.floor((a + b) / 2) >>> int((a + b) / 2) >>> (a + b) // 2   eumiro 15
41. >>> round(x)   eumiro 16
42. >>> round(x) >>> round(x, 2)   eumiro 16
43. >>> round(x) >>> round(x, 2) >>> f'x={x:.2}' x=1.23   eumiro 16
44. >>> round(x) >>> round(x, 2) >>> f'x={x:.2}' x=1.23 >>> f'{x=:.2}' x=1.23   eumiro 16
45. Percentages >>> perc = 1 / 7 * 100 >>> f'{perc:.1f}%' 14.3%   eumiro 17
46. Percentages >>> perc = 1 / 7 * 100 >>> f'{perc:.1f}%' 14.3% >>> ratio = 1 / 7 >>> f'{ratio:.1%}' 14.3%   eumiro 17
47. Numeric literals nanoseconds = seconds * 10e9   eumiro 18
48. Numeric literals nanoseconds = seconds * 10e9 nanoseconds = seconds * 1000000000   eumiro 18
49. Numeric literals nanoseconds = seconds * 10e9 nanoseconds = seconds * 1000000000 nanoseconds = seconds * 1_000_000_000   eumiro 18
50. Numeric literals nanoseconds = seconds * 10e9 nanoseconds = seconds * 1000000000 nanoseconds = seconds * 1_000_000_000 nanoseconds = seconds * 10**9   eumiro 18
51. pathlib.Path   eumiro 19
52. pathlib.Path parent = '/data' for fn in os.listdir(parent): stem, ext = os.path.splitext(fn) if ext == '.csv': fname = os.path.join(parent, fn) with open(fname, 'rb') as f: data = f.read() process(data)   eumiro 19
53. pathlib.Path parent = '/data' for fn in os.listdir(parent): stem, ext = os.path.splitext(fn) if ext == '.csv': fname = os.path.join(parent, fn) with open(fname, 'rb') as f: data = f.read() process(data) for path in Path('/data').glob('*.csv'): process(path.read_bytes())   eumiro 19
54. pathlib.Path parent = '/data' for fn in os.listdir(parent): stem, ext = os.path.splitext(fn) if ext == '.csv': fname = os.path.join(parent, fn) with open(fname, 'rb') as f: data = f.read() process(data) for path in Path('/data').glob('*.csv'): process(path.read_bytes()) if path.exists(): path.unlink() # and since Python 3.8: path.unlink(missing_ok=False)   eumiro 19
55. pathlib.Path and pytest def test_something(self): file = tempfile.NamedTemporaryFile(mode='w', delete=False) self.assertTrue(process(file)) os.unlink(file)   eumiro 20
56. pathlib.Path and pytest def test_something(self): file = tempfile.NamedTemporaryFile(mode='w', delete=False) self.assertTrue(process(file)) os.unlink(file) def test_something(tmp_path): assert process(tmp_path / 'something.dat')   eumiro 20
57. pathlib.Path and pytest def test_something(self): file = tempfile.NamedTemporaryFile(mode='w', delete=False) self.assertTrue(process(file)) os.unlink(file) def test_something(tmp_path): assert process(tmp_path / 'something.dat') /tmp/pytest-of-miro/pytest-1/test_something/something.dat   eumiro 20
58. datetime   eumiro 21
59. datetime >>> dt = datetime.datetime(1970, 1, 1) >>> calendar.timegm(dt.utctimetuple()) 0   eumiro 21
60. datetime >>> dt = datetime.datetime(1970, 1, 1) >>> calendar.timegm(dt.utctimetuple()) 0 >>> dt = datetime.datetime(1970, 1, 1, tzinfo=datetime.timezone.utc) >>> dt.timestamp() 0.0   eumiro 21
61. datetime >>> dt = datetime.datetime(1970, 1, 1) >>> calendar.timegm(dt.utctimetuple()) 0 >>> dt = datetime.datetime(1970, 1, 1, tzinfo=datetime.timezone.utc) >>> dt.timestamp() 0.0 try: import zoneinfo except ImportError: from backports import zoneinfo now = datetime.datetime.now(zoneinfo.ZoneInfo('Europe/Berlin'))   eumiro 21
62. time.time() >>> start = time.time() >>> run_expensive_operation() >>> end = time.time() >>> end - start   eumiro 22
63. time.time() >>> start = time.time() >>> run_expensive_operation() >>> end = time.time() >>> end - start >>> time.perf_counter()   eumiro 22
64. time.time() >>> start = time.time() >>> run_expensive_operation() >>> end = time.time() >>> end - start >>> time.perf_counter() >>> time.process_time()   eumiro 22
65.   eumiro 23
66. Should We Return to Python 2? 24
67. Should We Return to Python 2? Here's the plan: When someone uses a feature you don't understand, simply shoot them. This is easier than learning something new, and before too long the only living coders will be writing in an easily understood, tiny subset of Python 0.9.6 . — Tim Peters, 2002 24
68. Should We Return to Python 2? Here's the plan: When someone uses a feature you don't understand, simply shoot them. This is easier than learning something new, and before too long the only living coders will be writing in an easily understood, tiny subset of Python 0.9.6 . — Tim Peters, 2002 Miroslav Šedivý   eumiro 24