PEP 572: The Walrus Operator

A discussion on Python Governance, an introduction to PEP 572 and the walrus operator, as well as the resulting fallout.

1. AUSTIN PYTHON MEETUP AUGUST 2018
2. HI, I'M DUSTIN
3. PEP 572
4. PYTHON GOVERNANCE
5. BDFL BENEVOLENT DICTATOR FOR LIFE
7. PEP PYTHON ENHANCEMENT PROPOSAL
8. PEP 8 STYLE GUIDE FOR PYTHON CODE
9. PEP 8 STYLE GUIDE FOR PYTHON CODE AUTHOR: GUIDO VAN ROSSUM
10. PEP 20 THE ZEN OF PYTHON
11. PEP 20 THE ZEN OF PYTHON AUTHOR: TIM PETERS
12. PEP 566 METADATA FOR PYTHON SOFTWARE PACKAGES 2.1
13. PEP 566 METADATA FOR PYTHON SOFTWARE PACKAGES 2.1 AUTHOR: DUSTIN INGRAM
14. BDFL DELEGATES
15. 1) DRAFT 2) ACCEPTANCE 3) IMPLEMENTATION
16. PEP 572
17. :=
20. PROBLEMS
21. match = pattern.search(data) if match is not None: do_something(match)
22. chunk = file.read(8192) while chunk: process(chunk) chunk = file.read(8192)
23. foo = [f(x), f(x)**2, f(x)**3]
24. y = f(x) foo = [y, y**2, y**3]
25. results = [] for x in data: result = f(x) if result is not None: results.append(result)
26. filtered_data = [ f(x) for x in data if f(x) is not None ]
27. SOLUTIONS
28. match = pattern.search(data) if match is not None: do_something(match)
29. if (match := pattern.search(data)) is not None: do_something(match)
30. chunk = file.read(8192) while chunk: process(chunk) chunk = file.read(8192)
31. while chunk := file.read(8192): process(chunk)
32. foo = [f(x), f(x)**2, f(x)**3]
33. foo = [y := f(x), y**2, y**3]
34. results = [] for x in data: result = f(x) if result is not None: results.append(result)
35. filtered_data = [ f(x) for x in data if f(x) is not None ]
36. filtered_data = [ y for x in data if (y := f(x)) is not None ]
37. WHY?
38. LESS LINES ARE BETTER
39. foo = [y := f(x), y**2, y**3]
40. y = f(x) foo = [y, y**2, y**3]
41. LESS LINES ARE MORE EFFICIENT?
42. match = re.match(data) group = match.group(1) if match else None
43. group = re.match(data).group(1) if re.match(data) else None
44. group = match.group(1) if (match := re.match(data)) else None
45. SCOPE
46. foo = 'foo' if (foo := 'bar') is not None: do_something(...) print(foo)
47. EXCEPTIONS!
48. if any((comment := line).startswith('#') for line in lines): print("First comment:", comment) else: print("There are no comments")
49. if all((nonblank := line).strip() == '' for line in lines): print("All lines are blank") else: print("First non-blank line:", nonblank)
50. total = 0 partial_sums = [total := total + v for v in values] print("Total:", total)
51. =
52. x = y = z = 0 # Yes (z := (y := (x := 0))) # No
53. a[i] = x # Yes a[i] := x # No self.rest = [] # Yes self.rest := [] # No
54. x = 1, 2 # Sets x to (1, 2) (x := 1, 2) # Sets x to 1
55. total += tax # Yes total +:= tax # No
56. = VS. ==
57. PEP 572
58. RECEPTION
59. BACKWARDS COMPATIBILITY "WHERE WILL THIS WORK?"
60. TEACHABILITY "WHAT DO WE CALL THIS?"
61. ATTRACTIVENESS "IT'S JUST UGLY!"
66. TIM PETERS: "THE CURRENT PROPOSAL WOULD HAVE ALLOWED A MODEST BUT CLEAR IMPROVEMENT IN QUITE A FEW BITS OF CODE."
67. BARRY WARSAW: "SINCE IT CHANGES THE SYNTAX OF THE LANGUAGE, PEOPLE TEND TO FOCUS ON THAT WITHOUT UNDERSTANDING THE DEEPER SEMANTIC ISSUES."
68. ŁUKASZ LANGA: "DICTATORS SHOULD DICTATE"
69. GUIDO VAN ROSSUM: HAD TO STOP READING THE THREADS SO HE WOULDN'T "GO INSANE"
72. QUESTIONS
73. WHAT DOES THIS MEAN FOR PYTHON?
74. IT'S GOING TO BE OK
75. WILL THIS BECOME PART OF PYTHON?
76. PROBABLY (IN 3.8)
77. BUT I DON'T LIKE IT!
78. THEN DON'T WRITE IT!
79. IS GUIDO COMING BACK?
80. PROBABLY NOT
81. WILL THIS HAPPEN AGAIN?
82. PROBABLY NOT
83. ¯\_(ϑ)_/¯
84. THANKS!