Python 3.0: Where we break all your code

Transcript

1. Python 3.0 where we break all your code Abhinav Sarkar abhinav@abhinavsarkar.net abhinav.sarkar@gmail.com BARCAMP BANGALORE 7
2. introduction
3. xkcd#365
4. python 3.0 aka Python 3000 aka Py3k aka p3yk
5. where we break all your code
6. backwards incompatible
7. more precisely:
8. almost every program will need changes
9. almost every program will need changes
10. xkcd#349
11. justifications
12. Python is 16 years old
13. b/w compatibility is important
14. python: pre 1.0 lots of changes
15. 1.0 -> 2.0 2.0 -> 2.6
16. no b/w incompatible changes
17. none important enough to give presentations on
18. annoying features
19. py3k is the chance to fix
20. mistakes duplications ugly things
21. mistakes coerce() backticks
22. duplication TIOOWTDI not true
23. map list comprehensions
24. string functions string methods
25. apply(foo, args, kwargs) foo(*args, **kwargs)
26. email package rfc822 modules
27. how did this happen?
28. ugly
29. `backticks` repr()
30. reduce() sum() replaces 95% of uses
31. print >> somefile, “stuff”
32. smaller language == better language
33. “python fits in your brain”
34. easier to learn easier to use
35. 3.0
36. language changes
37. <> -> !=
38. `backticks` -> repr()
39. removed: print statement
40. !!
41. print() now a function
42. print a, b, c -> print(a, b, c)
43. print >> fp, “stuff” -> print(“stuff”, file=fp)
44. new print feature: customize separators
45. print “,”.join((a,b,c,d)) -> print(a,b,c,d, sep=“,”)
46. new string formatting
47. str.format() “name: {0} {1}”.format(first, last) fmt = “name: {first} {last}” fmt.format(first=“abhinav”, last=“sarkar”)
48. format() builtin >>> format(3.0, “06.1f”) '0003.0'
49. new keywords: as True False None nonlocal
50. basic types
51. strings
52. unicode string default
53. but sometimes you want bytes network protocols binary files
54. bytes() bytes([0x0A, 0x0B, 0x42]) bytes(string, encoding)
55. new ascii() builtin and “%a” string format
56. non-ascii identifiers
57. numbers
58. no more long() ints are long by default no more 123L
59. integer division >>> 1/2 0.5
60. old style >>> 1//2 0
61. dicts
62. dictob.has_key(key) -> key in dictob
63. removed: dict.iter*
64. instead: dictionary views
65. for k in dict: for k,v in dict.items():
66. sets
67. set literals {1,2,3}
68. {} == dict() empty set: set()
69. set comprehensions
70. iterables
71. next() -> __next__()
72. new feature unpacking: first, *rest, last = list
73. head, *rest = somelist *ignore, tail = somelist
74. map(), filter(), zip() -> iterators
75. exceptions
76. no more string exceptions exceptions must derive from BaseException
77. 2-arg raise raise MyExcp, val -> raise MyExcp(val)
78. 3-arg raise raise MyExcp, val, tback -> raise MyExcp(val).with_traceback(tback)
79. except excp, e -> except excp as e
80. classes
81. new classes only as old-style classes
82. class A(object) -> class A()
83. class decorators @decorator class MyClass: pass
84. more more powerful metaclasses Abstract Base Classes (ABC) abstract methods @abstractproperty
85. functions
86. keyword only args can't be positional
87. buggy example: def fun(arg1, arg2, flag=False): pass fun(1,2,3) # flag = 3 ??
88. the change: keyword args after *args
89. def fun(arg1, arg2, *, flag=False): pass >>> fun(1,2,3) Traceback (most recent call last): File “<stdin>”, line 1, in <module> TypeError: fun() takes exactly 2 positional arguments (3 given)
90. annotations
91. attaching metadata to arguments
92. syntax: def func(arg: expression)->returnValue: pass
93. expressions can be anything
94. documentation def doEvil(plan: “a plan”) -> “evil results”: .... types def foo(a: float, b: int, c:list) -> dict: .... more complex def processFiles(*files: “one or more of filenames”, delete: “delete when done” = False) -> “a boolean”: ....
95. Python ignore annotations
96. stored in __annotations__
97. 3rd party tools: optimizers, docs, IDEs, typechecking, ...
98. files
99. text vs binary text files must have encoding produce unicode binary files produce bytestrings
100. new I/O layer raw I/O buffered I/O text I/O
101. modules
102. absolute imports
103. import foo always imports from the top level
104. import from same package: from . import foo
105. import from parent package: from .. import foo
106. stdlib
107. goals: PEP8 compliance some structure cleaning out cruft
108. PEP 0008 “Modules should have short, all-lowercase names.”
109. BaseHTTPServer cPickle cStringIO HTMLParser ....
110. either renamed, or Flushed.
111. structure
112. current structure
113. duplication and near duplications bsddb gdbm dbm dumbdbm
114. urllib vs urllib2
115. new packages: http html xmlrpc json dbm urllib
116. lots of renames: cStringIO -> io.StringIO SocketServer -> socketserver httplib -> http.client urllib + urllib2 -> urllib
117. cruft
118. lots of purges: old email modules old hash modules old platform modules
119. thread gone use threading
120. UserDict and friends -> subclass from dict
121. porting approach
122. take 2.5 code get working on 2.6 turn -3 flag while True: run through 2to3 run unit tests under 3.0 fix 2.x code
123. 2.x -> 2.6 -> 3.0
124. python 2.6 interim release -3 flag: turns on warnings from __future__ from future_builtins import enables some backports
125. 2to3 ships with 2.6, 3.0 does mechanical rewrites handles a lot never going to be perfect
126. unit tests
127. eventually ... drop 2.x version switch to 3.0 version
128. things not in py3k
129. antigravity xkcd#353
130. case insensitivity death to lambda implicit self macros
131. not a complete rewrite
132. what happens to python 2.x?
134. 2.x is not going away will continue to be supported
135. please try 3.0 betas
136. (and report bugs and send fixes)
137. References PEPs http://www.python.org/dev/peps/ http://www.python.org/dev/peps/pep-3100/ Anthony Baxter's OSCON'08 Talk http://www.interlink.com.au/anthony/tech/talks/OSCON2008/
138. exit()