How to port a Python program to Ruby

Question

I'm trying to port a Python program to Ruby but I'm completely ignorant about Python.

Could you give me any advice?

I want to run sampletrain method. However, I dont understand why features=self.getfeatures(item) is available. getfeatures is just an instance variable, isn't it? It seem to be used as a method.

docclass.py:

class classifier:
  def __init__(self,getfeatures,filename=None):
    # Counts of feature/category combinations
    self.fc={}
    # Counts of documents in each category
    self.cc={}
    self.getfeatures=getfeatures

  def train(self,item,cat):
    features=self.getfeatures(item)
    # Increment the count for every feature with this category
    for f in features:
      self.incf(f,cat)

    # Increment the count for this category
    self.incc(cat)
    self.con.commit()

  def sampletrain(cl):
    cl.train('Nobody owns the water.','good')
    cl.train('the quick rabbit jumps fences','good')
    cl.train('buy pharmaceuticals now','bad')
    cl.train('make quick money at the online casino','bad')
    cl.train('the quick brown fox jumps','good')

Here's a guess: perhaps the second argument passed in during initialization is a a function; though it's assigned to a property during initialization, it can be invoked later on with parens. (This is similar to JavaScript, but not Python.) — Phrogz
– Phrogz, Commented Nov 15, 2011 at 13:53
@ThiefMaster and steenslag :) just to work.. thanks your nice comments. — zono
– zono, Commented Nov 15, 2011 at 14:09
@Phrogz 'similar to JS' is easy to understand for me. thanks — zono
– zono, Commented Nov 15, 2011 at 14:14

mikej · Accepted Answer · 2011-11-15 13:59:47Z

5

In Python, because the brackets for a method call aren't optional it is possible to distinguish between a reference to a method and an invocation of a method. i.e.

def example():
    pass

x = example # x is now a reference to the example 
            # method. no invocation takes place
            # but later the method can be called as
            # x()

vs.

x = example() # calls example and assigns the return value to x

Because the brackets for a method call are optional in Ruby you need to use some extra code e.g. x = method(:example) and x.call to achieve the same thing.

answered Nov 15, 2011 at 13:59

mikej

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mikej Over a year ago

You should be able to use either the style I've given above or write initialize to accept a block as suggested by tokland depending on whether you're likely to want to provide a named method or an anonymous block for the getfeatures functionality. If you need any more details, just let me know.

tokland · Accepted Answer · 2011-11-15 14:25:22Z

3

The idiomatic way to send behaviours in Ruby (since getfeatures in your code is clearly a callable) is to use blocks:

class Classifier
  def initialize(filename = nil, &getfeatures)
    @getfeatures = getfeatures
    ...
  end

  def train(item, cat)
    features = @getfeatures.call(item)
    ...
  end

  ...
end

Classifier.new("my_filename") do |item|
  # use item to build the features (an enumerable, array probably) and return them
end

edited Nov 15, 2011 at 14:25

answered Nov 15, 2011 at 14:15

tokland

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Comments

Marnen Laibow-Koser · Accepted Answer · 2011-11-15 15:02:40Z

2

If you're translating from Python, you'll have to learn Python so you're not "completely ignorant" about it. No short cuts.

answered Nov 15, 2011 at 15:02

Marnen Laibow-Koser

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