Help, In the middle of translating Python script to Scala

Question

I'm trying to translate: http://thinkstats.com/survey.py this script.

So here's what I'm translating right now (Python):

"""This file contains code for use with "Think Stats",
by Allen B. Downey, available from greenteapress.com

Copyright 2010 Allen B. Downey
License: GNU GPLv3 http://www.gnu.org/licenses/gpl.html
"""

import sys
import gzip
import os

class Record(object):
    """Represents a record."""

class Respondent(Record): 
    """Represents a respondent."""

class Pregnancy(Record):
    """Represents a pregnancy."""

Scala:

import sys.process._
import java.util.zip.GZIPInputStream
import java.io._

class Record[T](val obj: T)

class Respondent[T](val record: Record[T])

class Pregnancy[T](val record: Record[T])

Question: Did I do the class Respondent and the class Pregnancy correctly? Is the type annotation correct for these class? Is the logic correct? I've just read up on type parameterization so I'm a bit iffy on this and wanted to see if I'm on the correct path.

Thank you for your time.

It may be correct -- I'm not sure. What does the type parameter T used for? — Owen
– Owen, Commented Sep 8, 2011 at 2:06
@Owen I dunno yet. I just know it's taking a parameter of type Object in. It might be a stream, so therefore I just annotate it as a type T. And when I declare Respondent and Pregnancy class, I get an error because Record takes a parameter, so I ended up annotating the Record type in Respondent and Pregnancy parameter. >____< — mythicalprogrammer
– mythicalprogrammer, Commented Sep 8, 2011 at 2:10
Usually you use a type parameter if there can be different kinds of that class, so, for example, you could have a Record[Int] be a record that holds an Int. I'm pretty sure it makes sense for Record, but I'm not sure about Respondent -- do different kinds of respondents have different kinds of records? — Owen
– Owen, Commented Sep 8, 2011 at 2:17
@Owen Hmmm... but you can't exactly do class Respondent(val record: Record) because Record actually needs to take in something. And having a fix [t] type of record actually solve this since I don't know what type of parameter Record is taking in yet.. — mythicalprogrammer
– mythicalprogrammer, Commented Sep 8, 2011 at 3:11

Kipton Barros · Accepted Answer · 2011-09-08 02:35:30Z

5

As I recall, the Python syntax you're showing is for class extension (inheritance). The equivalent Scala would be

/** Represents a record.
 */
class Record

/** Represents a respondent.
 */
class Respondent extends Record

/** Represents a pregnancy.
 */
class Pregnancy extends Record

Scala comments of the form /** ... */ will show up as documentation in ScalaDoc.

Type parameterization isn't needed here. Its main use is to allow classes to accept or return values of an arbitrary parameterized type. For example, List[Int] and List[String] are lists of integers and strings respectively.

answered Sep 8, 2011 at 2:35

Kipton Barros

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1 Comment

mythicalprogrammer Over a year ago

Thank you. Did a quick google to confirm this, very surprise/shock on how Python does inheritance.

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