Rystad Energy Software Engineer
Interview Guide

import json
import math

def select_assets(raw):
    data = json.loads(raw)
    if not isinstance(data, dict) or not isinstance(data.get("assets"), list):
        raise ValueError("assets must be a list")
    selected, rejected, seen = [], [], set()
    for i, row in enumerate(data["assets"]):
        if not isinstance(row, dict):
            rejected.append((i, "row must be an object"))
            continue
        asset_id, capacity = row.get("id"), row.get("capacity")
        valid_number = (type(capacity) in (int, float)
                        and math.isfinite(capacity) and capacity >= 0)
        if not isinstance(asset_id, str) or not asset_id.strip():
            rejected.append((i, "invalid id"))
        elif row.get("unit") != "MW" or not valid_number:
            rejected.append((i, "capacity must be finite nonnegative MW"))
        elif type(row.get("active")) is not bool:
            rejected.append((i, "active must be a boolean"))
        elif row["active"] and capacity >= 100 and asset_id not in seen:
            seen.add(asset_id)
            selected.append(asset_id)
    return selected, rejected

sample = '{"assets":[{"id":"wind-1","capacity":120,"unit":"MW","active":true},' \
         '{"id":"solar-1","capacity":80,"unit":"MW","active":true},' \
         '{"id":"bad-1","capacity":true,"unit":"MW","active":true}]}'
assert select_assets(sample) == (["wind-1"], [(2, "capacity must be finite nonnegative MW")])
assert select_assets('{"assets":[]}') == ([], [])
assert select_assets('{"assets":[{"id":"x","capacity":100,"unit":"MW","active":true}]}')[0] == ["x"]

from dataclasses import dataclass
from abc import ABC, abstractmethod

@dataclass(frozen=True)
class BatchResult:
    selected: tuple
    rejected: tuple

class AssetSource(ABC):
    @abstractmethod
    def read(self):
        raise NotImplementedError

class JsonSource(AssetSource):
    def __init__(self, raw):
        self._raw = raw
    def read(self):
        selected, rejected = select_assets(self._raw)
        return BatchResult(tuple(selected), tuple(rejected))

assert JsonSource('{"assets":[]}').read() == BatchResult((), ())

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import json
import math

def select_assets(raw):
    data = json.loads(raw)
    if not isinstance(data, dict) or not isinstance(data.get("assets"), list):
        raise ValueError("assets must be a list")
    selected, rejected, seen = [], [], set()
    for i, row in enumerate(data["assets"]):
        if not isinstance(row, dict):
            rejected.append((i, "row must be an object"))
            continue
        asset_id, capacity = row.get("id"), row.get("capacity")
        valid_number = (type(capacity) in (int, float)
                        and math.isfinite(capacity) and capacity >= 0)
        if not isinstance(asset_id, str) or not asset_id.strip():
            rejected.append((i, "invalid id"))
        elif row.get("unit") != "MW" or not valid_number:
            rejected.append((i, "capacity must be finite nonnegative MW"))
        elif type(row.get("active")) is not bool:
            rejected.append((i, "active must be a boolean"))
        elif row["active"] and capacity >= 100 and asset_id not in seen:
            seen.add(asset_id)
            selected.append(asset_id)
    return selected, rejected

sample = '{"assets":[{"id":"wind-1","capacity":120,"unit":"MW","active":true},' \
         '{"id":"solar-1","capacity":80,"unit":"MW","active":true},' \
         '{"id":"bad-1","capacity":true,"unit":"MW","active":true}]}'
assert select_assets(sample) == (["wind-1"], [(2, "capacity must be finite nonnegative MW")])
assert select_assets('{"assets":[]}') == ([], [])
assert select_assets('{"assets":[{"id":"x","capacity":100,"unit":"MW","active":true}]}')[0] == ["x"]

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import json
import math

def select_assets(raw):
    data = json.loads(raw)
    if not isinstance(data, dict) or not isinstance(data.get("assets"), list):
        raise ValueError("assets must be a list")
    selected, rejected, seen = [], [], set()
    for i, row in enumerate(data["assets"]):
        if not isinstance(row, dict):
            rejected.append((i, "row must be an object"))
            continue
        asset_id, capacity = row.get("id"), row.get("capacity")
        valid_number = (type(capacity) in (int, float)
                        and math.isfinite(capacity) and capacity >= 0)
        if not isinstance(asset_id, str) or not asset_id.strip():
            rejected.append((i, "invalid id"))
        elif row.get("unit") != "MW" or not valid_number:
            rejected.append((i, "capacity must be finite nonnegative MW"))
        elif type(row.get("active")) is not bool:
            rejected.append((i, "active must be a boolean"))
        elif row["active"] and capacity >= 100 and asset_id not in seen:
            seen.add(asset_id)
            selected.append(asset_id)
    return selected, rejected

sample = '{"assets":[{"id":"wind-1","capacity":120,"unit":"MW","active":true},' \
         '{"id":"solar-1","capacity":80,"unit":"MW","active":true},' \
         '{"id":"bad-1","capacity":true,"unit":"MW","active":true}]}'
assert select_assets(sample) == (["wind-1"], [(2, "capacity must be finite nonnegative MW")])
assert select_assets('{"assets":[]}') == ([], [])
assert select_assets('{"assets":[{"id":"x","capacity":100,"unit":"MW","active":true}]}')[0] == ["x"]

from functools import wraps

def record_calls(events):
    def decorate(fn):
        @wraps(fn)
        def wrapped(*args, **kwargs):
            try:
                result = fn(*args, **kwargs)
            except Exception:
                events.append((fn.__name__, "failed"))
                raise
            events.append((fn.__name__, "ok"))
            return result
        return wrapped
    return decorate

events = []
instrumented = record_calls(events)(select_assets)
assert instrumented('{"assets":[]}') == ([], [])
assert instrumented.__name__ == "select_assets"
try:
    instrumented('not json')
except json.JSONDecodeError:
    pass
assert events == [("select_assets", "ok"), ("select_assets", "failed")]

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