Things you didn't know about Python

PyCon ZA 2012 presentation, not actually what the title says.

Transcript

1. Things you didn't know about Python a presentation by Armin Ronacher for PyCon South Africa 2012 @mitsuhiko http://lucumr.pocoo.org/
2. Things you didn't know about Python a presentation by Armin Ronacher for PyCon South Africa 2012 @mitsuhiko http://lucumr.pocoo.org/ might already know computers
3. Things you didn't know about Python a presentation by Armin Ronacher for PyCon South Africa 2012 @mitsuhiko http://lucumr.pocoo.org/ might already know computers and the world!!!11
4. Everything is horrible and nobody cares
5. We're doomed
7. [Untitled]
9. Motivation for this Talk Who am I and why this talk
10. Armin Ronacher Software Engineer at Fireteam Game Middleware Provider @mitsuhiko / @fireteamltd
11. We're using Python And not just us. Python has been popular in parts of in the gaming industry
12. I'm also doing Python Libraries and help people online using them.
14. What we can learn from Wifi Hotspots
15. Starting Somewhere Intended Login Mask
16. Down the Rabbit Hole Served by Apache, PHP 5.3, Directory Listings
17. *.php_backup source code? Check! SQL Injection? Check
18. Further … Register Globals? Check Debug Comments? Check
19. And Further GPL Violation? Check
20. Yay! Pre generated voucher PDF? Check
21. To Round it all Up Comes with Instructions
22. Priorities It's not secure if it does not have XML
24. A Step Back What do Wifi Hotspots have to do with anything?
25. Python is not perfect … but the criticism is very high level
26. “First World Problems” Most of our problems with Python are not stopping us from using the language. It just might make it less pleasant.
27. Who is using Python? Let's start with the marketing bits
28. Big Players NASA, Disney, Youtube, Google, etc.
29. Trivia: Microsoft shipped Python in 96 Microsoft Merchant Server was written in Python in 1996
30. But really everybody Python is one of the things that just shows up. If for nothing else, then build scripts.
31. Trivia: Dropbox uses Python Not just on the server, the client is also implemented in Python!
32. Gaming uses Python Demonware, Agora, EA/ESN, Fireteam
33. Nobody got fired for choosing Python
34. We are the IBM of Dynamic Languages
35. History Lessons A few interesting bits about the past
36. 1991: Where all started • Exceptions • Multiple Inheritance • C inspired IO system
37. Trivia: string.py was horrible It had O(n2) upper/lower functions
38. Trivia: what did this do until 2.5? raise ((a, b), c), d answer: raises exception a with value d
39. Trivia: mutex.py a module called mutex not actually a mutex survived until 2.7
40. 1995: The Huge Jump to 1.5 • Regular Expressions • Exceptions as classes • Built-in package support • Embeddable
41. Trivia: did you know re is 50% python? the regular expression compiler is written in Python You notice that when you python -mtrace
42. Trivia: why are builtin types lowercase? because they used to be functions the types where in types.py types.StringType was the type of a string (camelcase)
43. 2000: Modern Python: Python 2.0 • Unicode Support • Augmented assignments (+= etc.) • Garbage Collector • PEPs
44. 2004: Python as you know it • File encoding cookies • Boolean types • sets • reverse iteration • generator expressions
45. Trivia: 2.2.1 introduced True and False … but no boolean type. 2.2.0: no true/false 2.3.0: real boolean type
46. Today: Evolving Language • PyPy • Python 3
47. Reasons for Popularity key adopters and killer-apps
48. Really Early Adopters Math and Scientific Community Python's operator overloading and simple syntax was very convenient for scientific uses.
49. Trivia: Math Driven Syntax foo[1,...,2] == foo[(1, Ellipsis, 2)]
50. Other Factors Python was easy to extend with C extensions and starting with distutils it was possible to distribute them
51. Windows! Python has had excellent Windows support in the past unlike many other programming languages that were created in the POSIX environment
52. Trivia: Battlefield 2 used Python And since the engine is still used today there are free to play versions of Battlefield still using Python for scripting
53. Web Development We slowly and steadily became a proven platform for the web Python is not the final answer there but an amazing platform to start
54. Twisted If you wanted to do networking a few years ago Twisted was the answer
55. Trivia: Early XMPP Transports Most of the XMPP to X transports were written in Python with Twisted
57. But Really …
58. It's fun! People enjoy working with the language
59. I have yet to see a Wifi Hotspot Portal Page that is written in Python and sucks
60. Disclaimer: I understand that this statement is very optimistic and bad Python code exists in practice, that there are frameworks in the Python community that advocate for sloppy code, that there are widely used modules with security problems or bad general design, that there are indeed Wifi hotspot login pages that are horrible and indeed written in Python, that there are well written Wifi login pages in PHP (I don't actually believe that), that I am hugely biased and that my sample size is waaaaaaaaaaaaaaaaay too small.
61. “FUN!?” What is this?
62. Y U NO WORK
63. No Running into Walls
64. Descriptors Python's most important language feature
65. What are Descriptors? • __get__ • __set__ • __delete__ • Common descriptors: functions, properties
66. Trivia: Functions are Descriptors that's what makes them methods if placed within classes
67. Example: Basic Descriptor Lookup >>> class Foo(object): ... def my_function(self): ... pass ... >>> Foo.my_function <unbound method Foo.my_function> >>> Foo.__dict__['my_function'] <function my_function at 0x1002e1410> >>> Foo.__dict__['my_function'].__get__(None, Foo) <unbound method Foo.my_function> >>> >>> Foo().my_function <bound method Foo.my_function of <__main__.Foo object at 0x1002e2710>> >>> Foo.__dict__['my_function'].__get__(Foo(), Foo) <bound method Foo.my_function of <__main__.Foo object at 0x1002e2750>>
68. Example: Everyday Decorators >>> class Foo(object): ... @property ... def foo(self): ... return 'hello pycon' ... >>> Foo().foo 'hello pycon'
69. Cached Properties missing = object() class cached_property(object): def __init__(self, func): self.func = func self.__name__ = func.__name__ self.__doc__ = func.__doc__ self.__module__ = func.__module__ def __get__(self, obj, type=None): if obj is None: return self value = obj.__dict__.get(self.__name__, missing) if value is missing: value = self.func(obj) obj.__dict__[self.__name__] = value return value
70. Example: Cached Properties class Post(object): def __init__(self, text): self.text = text @cached_property def rendered_text(self): return markdown_to_html(self.text)
71. Duck Typing “if it's not a penguin it must be a duck”
72. ABDT: Abstract Base Duck Typing abstract bases for improved duck typing
73. Abstract Base Duck Typing • abc.ABCMeta — metaclass for abstract bases • collections.* — common abstract bases
74. Abstract Base Duck Typing callable(x) -> isinstance(x, Callable) tryexcept(hash(x)) -> isinstance(x, Hashable) tryexcept(iter(x)) -> isinstance(x, Iterable) tryexcept(len(x)) -> isinstance(x, Sized) tryexcept(hasattr(x, ‘__contains__’)) -> isinstance(x, Container) -> isinstance(x, Mapping) isinstance(x, Set) isinstance(x, Sequence) isinstance(x, MutableMapping) isinstance(x, MutableSet) isinstance(x, MutableSequence)
75. Example: Abstract Base Duck Typing >>> from collections import Iterator >>> class MyIter(object): ... def __iter__(self): ... return self ... def next(self): ... return 42 ... >>> isinstance(MyIter(), Iterator) True
76. Custom Ducks from abc import ABCMeta, abstractmethod class Markedup(object): __metaclass__ = ABCMeta @classmethod def __subclasshook__(cls, C): if cls is Markedup: if hasattr(C, "__html__"): return True return NotImplemented
77. Example: Custom Ducks >>> class Markup(unicode): ... def __html__(self): ... return self ... >>> isinstance(Markup('test'), Markedup) True
78. Debugging Helpers use internals to track down bugs
79. Tracking Imports import sys import __builtin__ real_import = __builtin__.__import__ def debug_import(name, locals=None, globals=None, fromlist=None, level=-1): glob = globals or sys._getframe(1).f_globals importer_name = glob and glob.get('__name__') or 'unknown' print '%s imports %s' % (importer_name, name) return real_import(name, locals, globals, fromlist, level) __builtin__.__import__ = debug_import
80. Example: Tracking Imports >>> import urlparse __main__ imports urlparse urlparse imports collections collections imports _abcoll collections imports _collections collections imports operator collections imports keyword collections imports sys collections imports heapq heapq imports itertools heapq imports operator heapq imports bisect bisect imports _bisect heapq imports _heapq collections imports itertools
81. Interpreter Frames def print_frame_info(frame): print 'module: %s' % frame.f_globals.get('__name__') print 'filename: %s' % frame.f_code.co_filename print 'current line: %d' % frame.f_lineno loc = dict((k, v) for k, v in frame.f_locals.iteritems() if not k.startswith('__')) print 'local variables: %s' % loc
82. Example: Interpreter Frames >>> import sys >>> print_frame_info(sys._getframe()) module: __main__ filename: <stdin> current line: 1 local variables: { 'a': 2, 'b': 4, 'sys': <module 'sys' (built-in)>, 'print_frame_info': <function print_frame_info at 0x100484668> }
83. Dumping Threads import sys import traceback def dump_threads(): for thread_id, frame in sys._current_frames().iteritems(): print 'Thread #%d' % thread_id print ''.join(traceback.format_stack(frame))
84. Example: Dumping Threads >>> import time, threading >>> def foo(): ... for x in xrange(10): ... time.sleep(1) ... >>> threading.Thread(target=foo).start() >>> dump_threads() Thread #4302381056 File "lib/python2.7/threading.py", line 483, in run self.__target(*self.__args, **self.__kwargs) File "<stdin>", line 3, in foo time.sleep(1) Thread #140735295412576 File "<stdin>", line 1, in <module> dump_threads() File "<stdin>", line 4, in dump_threads print ''.join(traceback.format_stack(frame)).rstrip()
85. Why we love Python and why we don't use other things
86. Win because awesome Fail This is how I “sell” Python
87. Slow Execution Monitor • Dump stacktrace if an API request runs longer than N seconds • Permanent background thread • Request start -> set marker • Request end -> remove marker • If marker active for more than N seconds -> log stacktrace
88. Remote Console • All Python code has a thread that listens for requests on redis • Can be used to execute arbitrary Python code for debugging • Sends results back to redis
89. Rich Logging • We log into Sentry error groups • all stacktraces on dev environments include local variables for all frames • Also speaks $language
90. Sentry Includes all information, groups automatically
91. Memory Leak Finding • Walk over all objects the garbage collector can reach • Resolve weak references • Group by type • Log to top grossing to graphite every second
92. Finding a Greenlet Leak Easy to track down what exactly is happening, ~40 lines of code
93. Killer Libraries • SQLAlchemy • lxml • *WSGI • $webframework
94. virtualenv • it does not matter that packaging or the import system is broken • it could be so much worse • virtualenv makes the big chaos into many separate small chaoses
95. Easy to Learn • Language can be picked up in weeks • It's a fun language to learn • It's very dynamic and leaves room for (crazy) experimentation
96. not insaneTM
97. An Amazing Community • Developers and people all around the world • embraces simple and truly open licenses • loves documentation • … now also loves testing
99. screw hackernews
101. & Worry Less get stuff done
103. Q&A http://fireteam.net/ — Armin Ronacher — @mitsuhiko