Go for Pythonistas

An overview of the Go programming language from the point of view of a seasoned Python developer.
golang, python

Transcript

1. Go for Pythonistas Francesc Campoy Flores Gopher at Google
2. Video A recording of this talk is available. youtu.be/elu0VpLzJL8 (http://youtu.be/elu0VpLzJL8)
3. Goal of this talk Whetting your appetite for Go
4. My tactics 1. Showing you how Go is like Python. 2. Showing you how Go is not like Python.
5. Python, Go, and me Software Engineer at Google: Feb 11-Aug 12 Lots of C++ and Python. SQL to C++ compiler in Python. Go Developer Relations: Aug 12 - d a t e t i m e . n o w ( ) Lots of Go.
6. Things I don't like about Python (it'll be short)
7. Beautiful and simple Dynamic typing - nice because it's concise, like Python. a = " h e l l o " b = 1 # b u t a l s o a = 2 Static typing - can be verbose, like Java or C++. F o o f o o = n e w F o o ( ) ; Static typing with inferred types, like Go. a : = " h e l l o " b : = 1 / / b u t n o a = 2 Statically-typed Python? Check mypy (http://www.mypy-lang.org/) and Cython (http://cython.org/) .
8. Run time pyrotechnics n a m e = ' p y t h o n i s t a ' # T h i s c o d e o n l y w o r k s h a l f o f t h e t i m e . i f r a n d o m . r a n d o m ( ) > 0 . 5 : p r i n t ' h e y ' + n a m e + ' , y o u w i n ! ' e l s e : p r i n t ' s o r r y ' + n a n e + ' , y o u l o s e ' I don't want start a flame war here but ... 100% code coverage is a symptom Code coverage should point you to untested cases. Not a way to find typos! 100% code coverage doesn't mean bug free.
9. Other things I don't like Deploying - managing dependencies. Performance - "not too slow" is often not fast enough. Magic! (e.g.: _ _ m a g i c _ _ : * * k a r g s , _ _ g e t a t t r _ _ ) A list of magic methods in Python: www.rafekettler.com/magicmethods.html (http://www.rafekettler.com/magicmethods.html)
10. And I *do* like concurrency! A lot has been said about Python's infamous Global Interpreter Lock. You should watch Mindblowing Python GIL (http://youtu.be/ph374fJqFPE) , by David Beazley.
11. Things I like about Python
12. Things I like about Python The Zen of Python. (Go and the Zen of Python (http://talks.golang.org/2012/zen.slide#1) ) Hashes and arrays are part of the language. The standard library. Magic! A bit of code can do a lot.
13. A bit of code
14. fib.py Have you ever heard of Fibonacci? d e f f i b ( n ) : a , b = 0 , 1 f o r i i n r a n g e ( n ) : a , b = b , a + b r e t u r n b d e f f i b _ r e c ( n ) : i f n < = 1 : r e t u r n 1 e l s e : r e t u r n f i b _ r e c ( n - 1 ) + f i b _ r e c ( n - 2 ) f o r x i n r a n g e ( 1 0 ) : p r i n t f i b ( x ) , f i b _ r e c ( x )
15. fib.go Something familiar? f u n c f i b ( n i n t ) i n t { a , b : = 0 , 1 f o r i : = 0 ; i < n ; i + + { a , b = b , a + b } r e t u r n b } f u n c f i b R e c ( n i n t ) i n t { i f n < = 1 { r e t u r n 1 } r e t u r n f i b R e c ( n - 1 ) + f i b R e c ( n - 2 ) } f u n c m a i n ( ) { f o r i : = 0 ; i < 1 0 ; i + + { f m t . P r i n t l n ( f i b ( i ) , f i b R e c ( i ) ) } } Run
16. Fibonacci without generators? What? Python generators are awesome. d e f f i b ( n ) : a , b = 0 , 1 f o r i i n r a n g e ( n ) : a , b = b , a + b y i e l d a Mechanically complex. f = f i b ( 1 0 ) t r y : w h i l e T r u e : p r i n t f . n e x t ( ) e x c e p t S t o p I t e r a t i o n : p r i n t ' d o n e ' But very easy to use. f o r x i n f i b ( 1 0 ) : p r i n t x p r i n t ' d o n e '
17. Python generators Note the generator executes concurrently. Hmm... I like concurrency.
18. Go concurrency Based on goroutines and channels. Goroutines: very light processing actors (the gophers). Channels: typed, synchronized, thread-safe pipes (the arrows).
19. "Generator" goroutines
20. "Generator" goroutines Uses a channel send instead of y i e l d . f u n c f i b ( c c h a n i n t , n i n t ) { a , b : = 0 , 1 f o r i : = 0 ; i < n ; i + + { a , b = b , a + b c < - a } c l o s e ( c ) } f u n c m a i n ( ) { c : = m a k e ( c h a n i n t ) g o f i b ( c , 1 0 ) f o r x : = r a n g e c { f m t . P r i n t l n ( x ) } } Run
21. "Generator" goroutines A more generator-like style: f u n c f i b ( n i n t ) c h a n i n t { c : = m a k e ( c h a n i n t ) g o f u n c ( ) { a , b : = 0 , 1 f o r i : = 0 ; i < n ; i + + { a , b = b , a + b c < - a } c l o s e ( c ) } ( ) r e t u r n c } f u n c m a i n ( ) { f o r x : = r a n g e f i b ( 1 0 ) { f m t . P r i n t l n ( x ) } } Run
22. Exercise: generating prime numbers Write a function that returns a channel and sends the first n prime numbers on it. Given the function p r i m e : / / p r i m e r e t u r n s t r u e i f n i s a p r i m e n u m b e r . f u n c p r i m e ( n i n t ) b o o l { f o r i : = 2 ; i < n ; i + + { i f n % i = = 0 { r e t u r n f a l s e } } r e t u r n t r u e } Use the Go playground: golang.org/s/go4py-ex1 (http://golang.org/s/go4py-ex1)
23. Solution: generating prime numbers f u n c p r i m e s ( n i n t ) c h a n i n t { c : = m a k e ( c h a n i n t ) g o f u n c ( ) { f o r i : = 1 ; n > 0 ; i + + { i f p r i m e ( i ) { c < - i n - - } } c l o s e ( c ) } ( ) r e t u r n c } f u n c m a i n ( ) { f o r p : = r a n g e p r i m e s ( 1 0 ) { f m t . P r i n t l n ( p ) } } Run
24. Exercise: Fibonacci primes Write a f i l t e r P r i m e s function that takes a channel of ints as a parameter and returns another channel of ints. All the prime numbers that f i l t e r P r i m e s receives from the input channel are sent into the output channel. Complete this code snippet: golang.org/s/go4py-ex2 (http://golang.org/s/go4py-ex2)
25. Solution: Fibonacci primes f u n c f i l t e r P r i m e s ( c i n c h a n i n t ) c h a n i n t { c o u t : = m a k e ( c h a n i n t ) g o f u n c ( ) { f o r v : = r a n g e c i n { i f p r i m e ( v ) { c o u t < - v } } c l o s e ( c o u t ) } ( ) r e t u r n c o u t } f u n c m a i n ( ) { f o r p : = r a n g e f i l t e r P r i m e s ( f i b ( 2 0 ) ) { f m t . P r i n t l n ( p ) } } Run
26. But there's much more Goroutines and channels aren't just for generators. They can be used to model all kinds of concurrent systems. To learn more: Concurrency patterns (http://talks.golang.org/2012/concurrency.slide#1) , by Rob Pike Advanced Concurrency Patterns (http://talks.golang.org/2013/advconc.slide#1) , by Sameer Ajmani
27. Object-oriented Go
28. Object-oriented Go A type declaration. t y p e N a m e s t r u c t { F i r s t s t r i n g M i d d l e s t r i n g L a s t s t r i n g } A method declaration. f u n c ( n N a m e ) S t r i n g ( ) s t r i n g { r e t u r n f m t . S p r i n t f ( " % s % c . % s " , n . F i r s t , n . M i d d l e [ 0 ] , s t r i n g s . T o U p p e r ( n . L a s t ) ) } Constructing a N a m e and using it. n : = N a m e { " W i l l i a m " , " M i k e " , " S m i t h " } f m t . P r i n t f ( " % s " , n . S t r i n g ( ) ) Run
29. Methods on anything There's more to types than structs. t y p e S i m p l e N a m e s t r i n g You can define methods on any type. f u n c ( s S i m p l e N a m e ) S t r i n g ( ) s t r i n g { r e t u r n s t r i n g ( s ) } Or almost any type. f u n c ( s s t r i n g ) N o W a y ( ) You can only define methods on types within the same package.
30. Duck typing
31. Duck typing If it walks like a duck ... What defines a duck? Is there an explicit list of "duck" features? What if the duck is not exactly a duck? s/duck/file-like object/g
32. Quack?
33. Go interfaces Simply a set of methods. From the f m t package: t y p e S t r i n g e r i n t e r f a c e { S t r i n g ( ) s t r i n g } f m t . P r i n t l n calls the String method if the parameter is a S t r i n g e r . A type with all the methods of the interface implements the interface. Implicit satisfaction == No "implements" Structural typing: it doesn't just sound like a duck, it is a duck. And that's checked at compile time. n = N a m e { " W i l l i a m " , " M i k e " , " S m i t h " } f m t . P r i n t l n ( n ) Run
34. Decorators
35. Decorators A convenient way to wrap a function. d e f a u t h _ r e q u i r e d ( m y f u n c ) : d e f c h e c k u s e r ( s e l f ) : u s e r = p a r s e _ q s ( u r l p a r s e ( s e l f . p a t h ) . q u e r y ) . g e t ( ' u s e r ' ) i f u s e r : s e l f . u s e r = u s e r [ 0 ] m y f u n c ( s e l f ) e l s e : s e l f . w f i l e . w r i t e ( ' u n k n o w n u s e r ' ) r e t u r n c h e c k u s e r A function can be decorated using @ . c l a s s m y H a n d l e r ( B a s e H T T P R e q u e s t H a n d l e r ) : @ a u t h _ r e q u i r e d d e f d o _ G E T ( s e l f ) : s e l f . w f i l e . w r i t e ( ' H e l l o , % s ! ' % s e l f . u s e r )
36. Decorators If we run it. t r y : s e r v e r = H T T P S e r v e r ( ( ' ' , P O R T _ N U M B E R ) , m y H a n d l e r ) s e r v e r . s e r v e _ f o r e v e r ( ) e x c e p t K e y b o a r d I n t e r r u p t : s e r v e r . s o c k e t . c l o s e ( ) This is unauthorized: localhost:8080/hi (http://localhost:8080/hi) This is authorized: localhost:8080/hi?user=john (http://localhost:8080/hi?user=john)
37. Decorators in Go? Not exactly, but close enough. Go doesn't provide decorators in the language, but its function literal syntax and simple scoping rules make it easy to do something similar. v a r h i H a n d l e r = a u t h R e q u i r e d ( f u n c ( w h t t p . R e s p o n s e W r i t e r , r * h t t p . R e q u e s t ) { f m t . F p r i n t f ( w , " H i , % v " , r . F o r m V a l u e ( " u s e r " ) ) } , ) A wrapper function. f u n c a u t h R e q u i r e d ( f h t t p . H a n d l e r F u n c ) h t t p . H a n d l e r F u n c { r e t u r n f u n c ( w h t t p . R e s p o n s e W r i t e r , r * h t t p . R e q u e s t ) { i f r . F o r m V a l u e ( " u s e r " ) = = " " { h t t p . E r r o r ( w , " u n k n o w n u s e r " , h t t p . S t a t u s F o r b i d d e n ) r e t u r n } f ( w , r ) } }
38. Decorators in Go? This is unauthorized: localhost:8080/hi (http://localhost:8080/hi) This is authorized: localhost:8080/hi?user=john (http://localhost:8080/hi?user=john) f u n c m a i n ( ) { h t t p . H a n d l e F u n c ( " / h i " , h i H a n d l e r ) h t t p . L i s t e n A n d S e r v e ( " : 8 0 8 0 " , n i l ) } Run
39. Exercise: errors in HTTP handlers In Go, functions can return errors to indicate that something bad happened. The n e t / h t t p package from the standard library defines the type H a n d l e r F u n c . t y p e H a n d l e r F u n c f u n c ( R e s p o n s e W r i t e r , * R e q u e s t ) But it's often useful to unify the error handling into a single function to avoid repetition. t y p e e r r o r H a n d l e r f u n c ( h t t p . R e s p o n s e W r i t e r , * h t t p . R e q u e s t ) e r r o r Write a decorator that given a e r r o r H a n d l e r returns a h t t p . H a n d l e r F u n c . If an error occurs it logs it and returns an http error page.
40. Exercise: errors in HTTP handlers (continuation) Given the function h a n d l e r . f u n c h a n d l e r ( w h t t p . R e s p o n s e W r i t e r , r * h t t p . R e q u e s t ) e r r o r { n a m e : = r . F o r m V a l u e ( " n a m e " ) i f n a m e = = " " { r e t u r n f m t . E r r o r f ( " e m p t y n a m e " ) } f m t . F p r i n t l n ( w , " H i , " , n a m e ) r e t u r n n i l } We want to use it as follows. h t t p . H a n d l e F u n c ( " / h i " , h a n d l e E r r o r ( h a n d l e r ) ) Implement h a n d l e E r r o r using the playground. golang.org/s/go4py-ex3 (http://golang.org/s/go4py-ex3)
41. Solution: errors in HTTP handlers f u n c h a n d l e E r r o r ( f e r r o r H a n d l e r ) h t t p . H a n d l e r F u n c { r e t u r n f u n c ( w h t t p . R e s p o n s e W r i t e r , r * h t t p . R e q u e s t ) { e r r : = f ( w , r ) i f e r r ! = n i l { l o g . P r i n t f ( " % v " , e r r ) h t t p . E r r o r ( w , " O o p s ! " , h t t p . S t a t u s I n t e r n a l S e r v e r E r r o r ) } } } / / F a k e r e q u e s t w i t h o u t ' n a m e ' p a r a m e t e r . r : = & h t t p . R e q u e s t { } w : = n e w D u m m y R e s p ( ) h a n d l e E r r o r ( h a n d l e r ) ( w , r ) f m t . P r i n t l n ( " r e s p a : " , w ) / / F a k e r e q u e s t w i t h ' n a m e ' p a r a m e t e r ' j o h n ' . r . F o r m [ " n a m e " ] = [ ] s t r i n g { " j o h n " } w = n e w D u m m y R e s p ( ) h a n d l e E r r o r ( h a n d l e r ) ( w , r ) f m t . P r i n t l n ( " r e s p b : " , w ) Run
42. Monkey patching
43. Monkey patching "A monkey patch is a way to extend or modify the run-time code of dynamic languages without altering the original source code." - Wikipedia
44. Monkey patching Also known as "duck punching" ... poor duck. Often used for testing purposes. For example, say we want to test this function: d e f s a y _ h i ( u s r ) : i f a u t h ( u s r ) : p r i n t ' H i , % s ' % u s r e l s e : p r i n t ' u n k n o w n u s e r % s ' % u s r Which depends on a function that makes an HTTP request: d e f a u t h ( u s r ) : t r y : r = u r l l i b . u r l o p e n ( a u t h _ u r l + ' / ' + u s r ) r e t u r n r . g e t c o d e ( ) = = 2 0 0 e x c e p t : r e t u r n F a l s e
45. Monkey patching We can test s a y _ h i without making HTTP requests by stubbing out a u t h : d e f s a y h i t e s t ( ) : # T e s t a u t h e n t i c a t e d u s e r g l o b a l s ( ) [ ' a u t h ' ] = l a m b d a x : T r u e s a y _ h i ( ' J o h n ' ) # T e s t u n a u t h e n t i c a t e d u s e r g l o b a l s ( ) [ ' a u t h ' ] = l a m b d a x : F a l s e s a y _ h i ( ' J o h n ' )
46. Gopher punching! The same effect can be achieved in Go. f u n c s a y H i ( u s e r s t r i n g ) { i f ! a u t h ( u s e r ) { f m t . P r i n t f ( " u n k n o w n u s e r % v \ n " , u s e r ) r e t u r n } f m t . P r i n t f ( " H i , % v \ n " , u s e r ) } Which depends on v a r a u t h = f u n c ( u s e r s t r i n g ) b o o l { r e s , e r r : = h t t p . G e t ( a u t h U R L + " / " + u s e r ) r e t u r n e r r = = n i l & & r e s . S t a t u s C o d e = = h t t p . S t a t u s O K }
47. Gopher punching! Our test code can change the value of auth easily. f u n c T e s t S a y H i ( ) { a u t h = f u n c ( s t r i n g ) b o o l { r e t u r n t r u e } s a y H i ( " J o h n " ) a u t h = f u n c ( s t r i n g ) b o o l { r e t u r n f a l s e } s a y H i ( " J o h n " ) } Run
48. Conclusion
49. Conclusion Go is a bit like Python simple flexible fun but a bit different too fast concurrent statically typed Disclaimer : "No pythons, ducks, monkeys or gophers were harmed while writing this talk"
50. Try it Next steps golang.org (http://golang.org) Learn Go from your browser tour.golang.org (http://tour.golang.org) The community: golang-nuts groups.google.com/d/forum/golang-nuts (https://groups.google.com/d/forum/golang-nuts)
51. Thank you Francesc Campoy Flores Gopher at Google http://campoy.cat (http://campoy.cat) @francesc (http://twitter.com/francesc) campoy@golang.com (mailto:campoy@golang.com)