Python 2 or Python 3? - (Finally) Understanding the differences between the two main versions of the language

1. Hello! I'm Yan Orestes Content creator on 1 @yanorestes
2. Python 2 X Python 3 Which version to learn? 2
3. Python 2 X Python 3 Which version to learn? Which version to code with? 3
4. Wait what about backward compatibility? 4
5. backward compatibility 5
6. design failures Python 2 6
7. design failures Python 3 7
8. 8 Python 2 or Python 3? (Finally) Understanding the differences between the two main versions of the language
9. Subtle changes 1. 9
10. Python 2 >>> print 'Hello, world!' Hello, world! 10
11. >>> print 'Hello, world!' File "<stdin>", line 1 print 'Hello, world!' ^ SyntaxError: Missing parentheses in call to 'print'. Did you mean print('Hello, world!')? Python 3 11
12. Python 2 & Python 3 >>> print('Hello, world!') Hello, world! 12
13. raw_input X input 13
14. raw_input X input Python 2 Python 3 14
15. Python 2 >>> input() Hello! Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<string>", line 1 Hello! ^ SyntaxError: unexpected EOF while parsing 15
16. Lazy evaluation 2. 16
17. range function X class 17
18. range function X class list instance Python 2 Python 3 18
19. Python 2 >>> range(10**10) Traceback (most recent call last): File "<stdin>", line 1, in <module> MemoryError 19
20. Python 3 >>> range(10000**10000) range(0,1000000000000000000000 00000000000000000000000000000 00000000000000000000000000000 00000000000000000000000000000 00000000000000000000000000000 00000000000000000000000000…) 20
21. Python 2 But what about xrange? 21
22. Python 2 >>> range(10**10) xrange(0,10000000000) 22
23. Python 2 >>> xrange(10000**10000) Traceback (most recent call last): File "<stdin>", line 1, in <module> OverflowError: Python int too large to convert to C long 23
24. Numbers 3. 24
25. large numbers long X int 25
26. Python 2 >>> sys.maxint 9223372036854775807 >>> sys.maxint + 1 9223372036854775808L >>> type(sys.maxint + 1) <type 'long'> 26
27. Python 3 >>> sys.maxsize 9223372036854775807 >>> sys.maxsize + 1 9223372036854775808 >>> type(sys.maxsize + 1) <class 'int'> 27
28. int division Python 2 X Python 3 int float 28
29. Python 2 >>> 4/2 2 >>> 3/2 1 29
30. Python 3 >>> 4/2 2.0 >>> 3/2 1.5 30
31. Python 2 e Python 3 >>> 3//2 1 >>> 3/2.0 1.5 31
32. "Text" 4. 32
33. Python 2 >>> type('Hello, world!') <type 'str'> >>> type(u'Hello, world!') <type 'unicode'> 33
34. Python 2 str unicode bytes texto 34
35. Python 2 >>> len('Ā') 2 >>> len(u'Ā') 1 35
36. Python 3 bytes str bytes text 36
37. Python 3 >>> type('Hello, world!') <class 'str'> >>> type(u'Hello, world!') <class 'str'> >>> type(b'Hello, world!') <class 'bytes'> 37
38. Python 3 >>> π = 3.14 >>> π 3.14 38
39. GIF identifier def is_gif(filename): with open(filename, 'rb') as f: id = f.read(6) return id == 'GIF89a' 39
40. id de GIFs Python 2 True Python 3 False 40
41. GIF identifier def is_gif(filename): with open(filename, 'rb') as f: id = f.read(6) return id == b'GIF89a' 41
42. Comparison 5. 42 • == != • > < • >= <=
43. 43 cmp e __cmp__ -1 (<), 0 (==), 1 (>)
44. 44 cmp e __cmp__ -1 (<), 0 (==), 1 (>)
45. 45 Python 2 all objects are ordinally comparable
46. 46 Python 2 all objects are ordinally comparable ??????????
47. 47 Python 2 >>> foo = MyClass() >>> foo < 'a' True >>> foo < 1 True >>> foo < [] True
48. 48 Python 2 >>> 999999999 < 'a' True >>> 999999999 < [] True >>> 999999999.99 < [] True
49. 49 Python 2 >>> ' ' > [] True >>> 'str' > 'list' True
50. 50 Python 3 >>> ' ' > [] Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: '>' not supported between instances of 'str' and 'list'
51. Indentation 6. 51
52. 52 Python 3 >>> while True: ... print('hello') ... print('bye') File "<stdin>", line 3 print('bye') ^ TabError: inconsistent use of tabs and spaces in indentation
53. 53 Which version to learn? (and which to teach?)
54. 54 Which version to code with?
55. 55 2014 - Python 2 78% X 22% Python 3
56. 56 2014 - Python 2 78% X 22% Python 3 2016 - Python 2 60% X 40% Python 3
57. 57 2014 - Python 2 78% X 22% Python 3 2016 - Python 2 60% X 40% Python 3 2017 - Python 2 25% X 75% Python 3
58. 58 Making your program more portable
59. Python 2 & Python 3 >>> print('Hello, world!') Hello, world!
60. from sys import version_info if version_info.major == 3: input() else: raw_input() 60
61. from sys import version_info if version_info.major == 3: input() else: raw_input() 61
62. from sys import version_info if version_info.major > 2: input() else: raw_input() 62
63. from sys import version_info if version_info.major > 2: input() else: raw_input() 63
64. EAFP
65. Sometimes it's easier to ask for forgiveness than permission 65 - Grace Hopper
66. try: raw_input('Enter your name: ') except NameError: input('Enter your name: ') 66
67. try: raw_input('Enter your name: ') except NameError: input('Enter your name: ') 67
68. Thank you! Any questions? You can talk to me here: ▪ @yanorestes ▪ yan.orestes@alura.com.br 68