What Ruby can learn from Python
(and vice versa)Reuven M. Lerner, PhD • [email protected]
Rails Israel 2014 November 4th, 2014
Who am I?• Programmer, consultant, developer, trainer
• Long-time Ruby, Python user
• Linux Journal columnist
• Author, Practice Makes Python!
• PhD in Learning Sciences from Northwestern
• Read (lots) more at http://lerner.co.il/
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Python, Ruby, and me
Sapir-Whorf Hypothesis
"Cognitive processes, such as thought and experience, may be influenced by the categories and patterns of the language a person speaks." — Wikipedia
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Or: You are what you speak!
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Learning a language helps you not only communicate,
but also to think in new ways
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你有叉⼦子吗？
Nǐ yǒu chāzi ma? Do you have a fork?
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Possible answers
• "Yes"
• "No"
• "What's a fork?"
• "Your accent is so bad, I have no idea what you're saying"
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The actual answer?
• None of the above!
• Chinese doesn't have words for "yes" and "no."
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你有叉⼦子吗？ Nǐ yǒu chāzi ma?
Do you have a fork?
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Answer： 有 (yǒu) "Have"
Can you think of another language that
works this way?
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בראשית כ״ט, ו׳
ויאמר, ״השלום לו?״ ויאמרו ״שלום.״
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Genesis 29:6
And he said, "Is he well?" And they said, "Well!" (i.e., "Yes!")
And also…
CREATE TABLE Foo (id SERIAL, stuff TEXT);
CREATE TABLE
INSERT INTO Foo (stuff) VALUES ('abc');
INSERT 0 1
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Comparing languages
• Appreciate each one more
• Reflect on the relative trade-offs
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Ruby and Python both…• … dynamically and strongly typed
• … are JIT byte-compiled
• … are cross-platform
• … are widely used for a variety of tasks
• … popular among Web developers
• … have multiple implementations
• … have an object system based (in part) on Smalltalk
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And yet
• Python and Ruby feel very different
• What can we learn from these differences?
• What can we learn from the Python world? (And what can they learn from us?)
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General attitude• Ruby wants to give you freedom, to allow you to be
creative and flexible, as in a natural language
• TMTOWTDI, POLS
• Python wants to restrict you, for your own good
• "There should be one — and preferably only one — obvious way to do it."
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The result?• Python is
• easier to learn
• easier to debug and maintain
• Ruby
• offers you richer options
• greater expressiveness
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Development process
• Python Enhancement Proposals (PEPs)
• Ruby could use such a system
• Heck, Rails could use such a system
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Backward compatibility• Historically, Python upgrades were conservative
• But not 2.x -> 3.x
• Ruby was less conservative, breaking things (especially going from 1.8 to 1.9/2.0)
• Maybe Python emphasis on compatibility and inclusiveness hurt the 3.x upgrade
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What is truth?
• Ruby: Everything is true, except for false and nil
• Python: Everything is true, except for None, False, 0, and empty data (e.g., '' or [])
• So: 0 is false in Python, but true in Ruby!
• But we all like #blank? and #present? in Rails…
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Everything is an object…
• In both Ruby and Python, everything is an object!
• But in Python, some objects are more equal than others…
• So you can't do this in Python:
5.times { puts "Hello" }
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Blocks
• Ruby people love blocks!
• Python doesn't have them.
• They create functions, and pass those
• Or they use lambdas (or not)
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Namespaces• Python has a single namespace for functions and
variables. So x can be an int, a str, or a function
• Ruby has two separate namespaces — one for methods, and one for data
• Ruby's approach can lead to surprises!
x = 10 # set a local variable
self.x = 10 # invoke an attr_ method
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Reserved words
• Python barely has any:
True, False = False, True
• Ruby lets us open built-in classes, but not this!
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Modern Python
• Fine, modern Python outlaws this. But it allows:
>>> str = [1,2,3]
>>> type(str)
<class 'list'>
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Scoping
• Python has clear rules for scoping: LEGB (local, enclosing function, global builtin)
• Ruby's scoping rules feel natural, but the rules aren't easy to learn or remember.
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Indentation• Newcomers to Python hate the indentation rules
• But I actually like them!
• Easy to read
• No annoying "end - end - end - end" all over
• Easy to see where code begins and ends
• That said, Ruby's syntax would never work with Python's indentation rules
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Parentheses• Needed in Python to invoke methods and create classes
• Makes it easier to pass functions as parameters
• Not needed in Ruby to invoke methods
• Makes DSLs cleaner, easier to write and read
• You cannot pass a method just by name; use method(:foo)
• DSLs in non-Ruby languages look far uglier, and look like the original language, not a new one
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Explicit return
• In Ruby, the value of the final line evaluated is the value of the method. We often don't say "return"
• In Python, if you don't say "return", then your method returns None
• I don't see an advantage to Python's behavior
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Attributes vs. methods• In Ruby, object state is private, and access is all done
through methods.
• Want to access data? Write a getter or setter
• Or use attr_*, and Ruby will write them for you
• In Python, object state is public
• Getters and setters are discouraged
• Want the logic of a getter or setter? Use a "property," which invokes a method when you access an attribute
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In other words• Ruby tries to make data look like methods
• Method calls are the fundamental form of inter-object communication
• Python tries to make methods look like data
• Attributes are open, and thus there is less need for methods to access data
• Besides, attributes exist in a single namespace
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Object model• In Ruby, the object model emphasizes methods
and inheritance of those methods
• What are your methods, and what are your superclass's methods?
• In Python, the object model emphasizes attributes and "inheritance" of those attributes
• What attributes are defined on an object, and what are define on its class?
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What is hard to learn?
• Each object model leads to something that is hard for people to understand
• In Ruby, you have to understand singleton classes (aka eigenclasses)
• In Python, you have to understand how attributes work, including attribute scoping rules
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Multiple inheritance vs. include/extend
• Python: Multiple inheritance is OK, if you do it right
• Ruby: You won't get it right. Use modules!.
• The inheritance tree is very easy to figure out
• Modules allow for mixins, the only good reason for multiple inheritance
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for loops vs. Enumerable
• In Ruby, we want to iterate over everything
• Implement #each in your class
• include Enumerable
• Now you get map, select, and many other methods
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for loops vs. Enumerable
• In Python, we also want to iterate over everything
• We do that with "for" loops and other global constructs (e.g., comprehensions)
• Our object plug into these constructs by implementing the iteration protocol
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list.sort's return type
• Python's, list.sort returns None, not the list
• In Ruby, we almost always return an object from a method, so that we can chain the method calls.
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Comprehensions• Python has comprehensions:
[str(x) for x in range(5)]
[x*x for x in range(5)]
[line.split(":")[0]
for line in open('/etc/passwd')]
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Sets and dicts• Set comprehensions
{word.strip()
for word in open('/usr/share/dict/words')}
• Dictionary comprehensions
{line.split(":")[0] : line.split(":")[2]
for line in open('/etc/passwd')
if line.startswith("#")}
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Comprehensible?
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No.
Ruby is more consistent• In Ruby, we use the block syntax everywhere
(0..4).map {|n| n.to_s}
(0..4).map {|n| n * n}
File.open('/etc/passwd').readlines.
map {|line| line.split(":")[0]}
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The Ruby versionHash[File.open('/etc/passwd').
readlines.
select {|line| line[0] != '#'}.
map {|line| line.split(":")}.
map {|row| [row[0], row[2]]} ]
• Longer, but more consistent
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Easy metaprogramming
• Metaprogramming is fun and easy in Ruby
• Python permits it, but discourages such things
• Most of the time, use decorators
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Oscar
Felix(Python)
(Ruby)
你们有问题吗？ יש לכם שאלות?
(Do you have any questions?)
[email protected] @reuvenmlerner http://lerner.co.il/
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