Python for Ruby Programmers

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Python for Ruby Programmers MIKE LEONE LA RUBYCONF 2013 FEB 23 2013

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This presentation: 1. Fast-paced 2. Python in 30 mins 3. It's easy!

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About Me

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Web Mobile Embedded

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That's it.

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Ruby: 2006 Python: 2010

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New appreciation Better Rubyist

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What we'll cover

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1. Example program 2. 13 Design similarities 3. 13 Differences 4. 5 Problem domains 5. “Feelings”

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What we WON'T cover

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1. Implementations 2. Performance (Good enough) 3. Parallelism (GIL) 4. Minor syntax (You'll get it)

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What I'll try to convince you:

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1. VERY similar! 2. You're already ready 3. Python = Better Rubyist 4. Hire a Pythonista

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Zen of Python (abridged)

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1. Explicit is better than implicit. 2. Flat is better than nested. 3. Readability counts. 4. There should be [only] one obvious way to do it. 5. Namespaces are a great idea -- let's do more of those!

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Example: Create a Person class

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1. Name and age 2. Can greet you 3. Knows if it's Beiber 4. Greets Google directors

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13 Similarities

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1. Dynamically Typed

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def print_object(some_sorta_object): print some_sorta_object.read() print_object(my_file) >>> “This is the file contents”

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2. Everything is an Object (even functions!)

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Python example: 5 + 3 >>> 8 (5).__add__(3) >>> 8 (5).__str__() >>> “5”

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3. Arrays

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things = [1, "hello", 2.5, 43] things[1] >> 'hello' Ruby (array)

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things = [1, "hello", 2.5, 43] things[1] >> 'hello' Python (list)

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4. Hash Tables

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color_map = { red: "#FF0000", purple: "#800080"} color_map[:red] >> "#FF0000" Ruby (hash)

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color_map = { "red": "#FF0000", "purple": "#800080"} color_map["red"] >> "#FF0000" Python (list)

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5. No special line terminators (no semicolons!)

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6. Strong functional programming paradigms

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def triple(number): return number * 3 list = [1, 2, 3, 4] map(triple, list) >>> [3, 6, 9, 12] Map

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def is_even(number): return number % 2 == 0 list = [1, 2, 3, 4] filter(is_even, list) >>> [2, 4] Filter

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list = [1, 2, 3, 4] map(lambda x: x *3, list) >>> [3, 6, 9, 12] Anonymous Functions (lambda)

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7. Awesome function parameters

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Optional / named arguments

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def greet(name, greeting="Hello"): print greeting + ", " + name greet("Bob") >>> Hello, Bob greet("Bob", greeting="Bonjour") >>> Bonjour, Bob greet("Bob", "Bonjour") >>> Bonjour, Bob

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Argument Unpacking

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def greet_everyone(*names): for name in names: print "Hello, " + name names = ["Bob", "Steve", "Jim"] greet_everyone(*names) Hello, Bob Hello, Steve Hello, Jim

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8. Raising Exceptions

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inputted_age = 30 if inputted_age > 25 raise ArgumentError, "must be under 26" end ArgumentError: must be under 26 (stack trace...) Ruby

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inputted_age = 30 if inputted_age > 25: raise ValueError("must be under 26") (stack trace...) ValueError: must be under 26 Python

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9. Handling Exceptions

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begin 23 / 0 puts "all good" rescue ZeroDivisionError puts "can't do that, bro" end >> can't do that, bro Ruby (rescue)

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try: 23 / 0 print “all good” except ZeroDivisionError: print "can't do that, bro" >> can't do that, bro Python (except)

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10. One-line conditionals

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“equal” if 3 == 3 >> “equal” 2 == 3 ? “equal” : “not equal” >> “not equal” Ruby

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if 3 == 3: “hello” >>> “hello” “equal” if 2==3 else “not equal” >> “not equal” Python

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11. Nice interactive shells

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$ python Python 2.7.3 (default) >>> 2 + 2 4 $ irb irb(main):001:0> 2 + 2 => 4

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12. Strong object reflection features

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steve = Person("Steve Ballmer", 54) steve.__dict__ >>> {'age': 54, 'name': 'Steve Ballmer'} steve.__class__ >>> dir(steve) # all methods/attrbutes ['GOOGLE_DIRECTORS', '__class__', '__delattr__', '__dict__', '__doc__', '__format__', '__getattribute__', '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'age', 'greet', 'greet_google_directors', 'is_justin_beiber', 'name', 'say_name_and_age']

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13. Radically simpler than C++/Java!

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13 Differences

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1. No blocks

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Blocks are the killer feature of Ruby

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1. Powerful metaprogramming 2. DSLs 3. Great frameworks (Rails)

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Decorators are a powerful Python feature similar to blocks.

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They let you inject or modify code in a function, like blocks. But not enough time.

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2. First-class Functions

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Functions as variables

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def add(a, b): return a + b def subtract(a, b): return a – b def process_numbers(a, b, func): return func(a, b) process_numbers(20, 5, add) >>> 25 process_numbers(20, 5, subtract) >>> 15

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Similar behavior is possible in Ruby, but you must wrap functions in procs.

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3. One-line lambdas, by design

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Can't do this in Python: [1, 2, 3, 4, 5].map do |num| if num % 3 == 0 0 elsif num % 4 == 0 num * 2 else num end end

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But do you really want to do that? 1. Harder to test 2. Harder to follow 3. Accidentally duplicate

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Python pushes you to factor things out into granular methods.

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def process_num(num): if num % 3 == 0: return 0 elif num %4 == 0: return num * 2 else: return num return map(process_num, [1,2])

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Python even supports inner methods to this end.

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def start_program(): def process_num(num): if num % 3 == 0: return 0 elif num %4 == 0: return num * 2 else: return num return map(process_num, [1,2])

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4. Python has “tuple,” an immutable list.

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[1, 2, 3] # can change (1, 2, 3) # can't change (Should be homogeneous, but not enforced)

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5. Python has more fine-grained importing

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require 'open-uri' result = open(“http://google.com”) Ruby You bring in everything from open-uri With lots of requires, which one is responsible?

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from urllib2 import urlopen response = urlopen(“http://google.com”) Python “Explicit is better than implicit.” You can write from urllib2 import * , but not a best practice.

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You can import any number of specific functions or variables from a python module(file).

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6. Python enforces indentation

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In practice, this is pretty awesome.

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Doesn't cause headaches. Makes code style more consistent.

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7. Python has more values that evaluate to False.

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False None (nil) [ ], (), {} ' ' 0

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8. Instead of Enumerable, Python has built-in functions

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filter() map() reduce()

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Convenient, but not as powerful as Enumerable.

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9. Python has simpler conditionals

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No case statements (use if... elif... else instead) if n == 0: print "You typed zero.\n" elif n== 1 or n == 9 or n == 4: print "n is a perfect square\n" elif n == 2: print "n is an even number\n" elif n== 3 or n == 5 or n == 7: print "n is a prime number\n"

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No “unless” unless !person.present? && !company.present? puts "do you even know what you're doing?" else puts "and now we're really confused" end

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10. No automatic return values

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Functions return None if they don't have an explicit “return” statement. def add(a, b): a + b add(2, 3) >>> None

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11. “self” as an argument to every class instance method

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Pro: Explicit No clashes with local variables or other imported objects Con: More verbose

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Class Person(object): def __init__(self, name): self.name = name def say_hi_to(self, name): print self.name + “ says hi to ” + name Person(“Steve”).say_hi_to(“Bob”) >>> “Steve says hi to Bob”

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12. No powerful module mixins like Ruby.

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Multiple inheritence only (yuck)

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13. Ruby has stronger metaprogramming features

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Python doesn't have define_method class_eval method_missing

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Can't reopen a class and extend it Can't extend built-in types (maybe for the better?)

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5 Problem Domains

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1. Web Development

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Ruby: Rails, Sinatra Ruby community is dominated by web development

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Python: Django, Zope, Flask, Pylons. Web dev is just one piece of the gigantic python community.

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2. Mobile Applications

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Neither language is popular for mobile apps. Interesting Ruby projects: Rhodes, RubyMotion.

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3. Desktop Applications

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Python has PyQT, wxPython, PyGTK. Ruby has shoes, wxRuby, RubyGTK, but not popular or mature.

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4. Scientific Programming

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Python has numpy, scipy. Widely used. Ruby doesn't have any mature scientifc/numeric libraries.

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5. Windows Deployment (if you must)

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Ruby: RailsInstaller is great. Doesn't target deployment. JRuby makes windows deployment much easier.

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But Python on windows is generally easier. Why? Because entire toolchain is well- supported. Windows neglect is self-perpetuating.

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The Python community is just bigger.

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“Feelings”

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It's harder to write code that pisses off other developers in Python.

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1. Smaller grammar 2. Forced indentation 3. Fewer ways to handle conditionals 4. The source of imported functionality is obvious 5. Explicit class and method structure makes code easier to follow.

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Ruby is more elegant, but in practice, Python is easier to read.

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Rails still wins for web development.

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Nothing as good as Rails will ever be implemented in Python. (metaprogramming, reflection)

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Need to hire a Rubyist? Hire a Pythonista instead.

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1. Ruby developer market is out of control. 2. There are more Python developers 3. Pythonistas can ramp up EASILY (hours/days, not weeks/months)

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Wrap-up

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1. VERY similar! 2. You're already ready 3. Python = Better Rubyist 4. Hire a Pythonista

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MIKE LEONE panopticdev.com leone.panopticdev.com @panopticdev @facebiff THANK YOU!