시장 및 거시 데이터 공급자 비교와 연결

# Provider Comparison: Multi-Source Data Acquisition


# Provider Comparison: Multi-Source Data Acquisition

**Docker image**: `ml4t`

## Purpose
Demonstrate the `ml4t.data.providers` unified `fetch_ohlcv()` interface
across YahooFinance, WikiPrices and FRED, then build a fallback strategy
and a price-level provider-comparison report. The notebook seeds the
ETF rotation universe used by the ETFs case study downstream.

## Learning Objectives
- Fetch OHLCV from multiple providers with one call signature.
- Build a priority-ordered fallback fetcher for production resilience.
- Quantify provider disagreement (row counts, price-difference stats)
  so multi-source stitching is auditable.
- Use FRED (vintage-aware) to pull macro series for risk overlays.

## Book reference
Chapter 2, §2.3 (multi-source stitching). The ETF universe materialised
here feeds the `case_studies/etfs/` pipeline.

## Prerequisites
- Network access for live YahooFinance + FRED calls (the notebook is a
  provider-acquisition demo — these are the only places in the
  publication pass where live API calls are intentional).
- WikiPrices parquet under `ML4T_DATA_PATH/equities/market/us_equities/us_equities.parquet`
  for the historical leg.
- `FRED_API_KEY` set (free signup) for §8.

```python
"""Provider Comparison — Multi-source data acquisition with ml4t-data providers."""

import os
from dataclasses import dataclass
from datetime import datetime, timedelta
from pathlib import Path

import numpy as np
import plotly.graph_objects as go
import polars as pl
from ml4t.data.providers import WikiPricesProvider, YahooFinanceProvider
from ml4t.data.providers.fred import FREDProvider

from utils.paths import display_path
from utils.style import COLORS, show_plotly_with_alt
```

### Declared parameters

`AS_OF_DATE` fixes the right-hand end of every window so the outputs are stable between
book editions rather than moving with the wall clock. Bump it when the book is revised.

`RISK_FREE_RATE` is subtracted in the Sharpe ratio in Section 7. It is a parameter rather
than a constant in the arithmetic because it is a choice, and a wrong one changes the
ordering of the table it feeds.

The FRED key is required only by Section 8, which is the last section, so the rest of the
notebook runs without it.

```python
AS_OF_DATE = "2025-01-15"
HISTORY_YEARS = 5

COMPARE_SYMBOL = "AAPL"
COMPARE_START = "2017-01-01"
COMPARE_END = "2017-12-31"
DISCREPANCY_PCT = 0.1  # a close difference above this is a discrepancy, not rounding
EXACT_MATCH_PCT = 0.01  # below this the two closes are the same number

RISK_FREE_RATE = 2.0  # percent per year, subtracted in the Sharpe ratio
TRADING_DAYS_PER_YEAR = 252

FRED_SERIES = ["VIXCLS", "DGS10"]
FRED_START = "2023-01-01"
FRED_END = "2024-01-01"
```

---

## Section 1: Understanding the Provider Architecture

ml4t-data provides a **unified interface** for fetching data from multiple sources. All providers inherit from `BaseProvider` and implement the same `fetch_ohlcv()` method.

### Key Benefits:
1. **Consistency**: Same API regardless of data source
2. **Validation**: Automatic OHLC invariant checks
3. **Polars Output**: `22_pandas_polars_benchmark` measures what that is worth here
4. **Rate Limiting**: Built-in throttling to avoid API bans
5. **Circuit Breaker**: Automatic failure detection and recovery

The table below lists the provider landscape. This notebook exercises Yahoo, WikiPrices and
FRED; the rest need API keys of their own and appear in the asset-class notebooks that use
them.

```python
providers_info = pl.DataFrame(
    {
        "provider": [
            "YahooFinanceProvider",
            "WikiPricesProvider",
            "FREDProvider",
            "EODHDProvider",
            "BinanceAPIProvider",
        ],
        "asset_class": [
            "US Equities, ETFs",
            "US Equities (Historical)",
            "Economic Indicators",
            "Global Equities",
            "Crypto",
        ],
        "api_key_required": [
            "No",
            "No (local file)",
            "Yes (free)",
            "Yes (free tier)",
            "No",
        ],
        "date_range": ["~30 years", "1962-2018", "50+ years", "~20 years", "~5 years"],
        "demonstrated_in": [
            "this notebook",
            "this notebook",
            "this notebook",
            "10_crypto_perps_eda",
            "10_crypto_perps_eda",
        ],
    }
)
providers_info
```

---

## Section 2: Fetching Data with Yahoo Finance

Yahoo Finance is the easiest starting point - no API key required. Let's fetch our ETF universe for the momentum strategy.

```python
# Define our ETF universe for the rotation strategy
ETF_UNIVERSE = ["SPY", "QQQ", "IWM", "EFA", "EEM", "TLT", "GLD"]

end_date = AS_OF_DATE
start_date = (
    datetime.strptime(AS_OF_DATE, "%Y-%m-%d") - timedelta(days=HISTORY_YEARS * 365)
).strftime("%Y-%m-%d")

print(f"Fetching data from {start_date} to {end_date}")
print(f"ETF Universe: {ETF_UNIVERSE}")
```

```python
# Create Yahoo Finance provider
yahoo = YahooFinanceProvider()

# Fetch SPY as our primary example
spy_data = yahoo.fetch_ohlcv("SPY", start_date, end_date)

print(f"Fetched {len(spy_data)} rows of SPY data")
print(f"Date range: {spy_data['timestamp'].min()} to {spy_data['timestamp'].max()}")
print("\nSample data:")
print(spy_data.head())
```

```python
# Examine the schema - ml4t-data provides consistent column names
print("Schema (consistent across all providers):")
for name, dtype in spy_data.schema.items():
    print(f"  {name}: {dtype}")
```

```python
# Fetch the full ETF universe — fail loudly on missing tickers
etf_data = {symbol: yahoo.fetch_ohlcv(symbol, start_date, end_date) for symbol in ETF_UNIVERSE}
print(
    f"Fetched {len(etf_data)}/{len(ETF_UNIVERSE)} ETFs · "
    f"{sum(len(d) for d in etf_data.values()):,} total daily rows"
)
```

```python
# Combine into a single DataFrame with symbol column
combined_dfs = []
for symbol, df in etf_data.items():
    combined_dfs.append(df.with_columns(pl.lit(symbol).alias("symbol")))

etf_universe_df = pl.concat(combined_dfs).sort(["symbol", "timestamp"])

(
    etf_universe_df.group_by("symbol")
    .agg(
        pl.col("timestamp").min().alias("start"),
        pl.col("timestamp").max().alias("end"),
        pl.len().alias("rows"),
        pl.col("close").last().alias("last_close"),
    )
    .sort("symbol")
)
```

---

## Section 3: Historical Data with WikiPrices

For long-term backtests (30+ years), Yahoo Finance has limitations. WikiPrices provides
long-horizon U.S. equity history (including many delisted names) from roughly 1962 to 2018.

**Key Advantage**: Includes delisted companies, but you still need explicit survivorship
checks and delisting return handling (see `08_survivorship_bias_detection`).

```python
from utils import ML4T_DATA_PATH

WIKI_PATHS = [
    # Primary: canonical layout under ML4T_DATA_PATH
    ML4T_DATA_PATH / "equities" / "market" / "us_equities" / "us_equities.parquet",
    # Docker mount (same nested layout)
    Path("/data/equities/market/us_equities/us_equities.parquet"),
    # Test fixture (CI subset)
    Path("/app/tests/fixtures/data/equities/market/us_equities/us_equities.parquet"),
    Path("tests/fixtures/data/equities/market/us_equities/us_equities.parquet"),
]

wiki = None
wiki_path_used = None
wiki_load_errors = []
```

### WikiPrices Schema Adapter

When WikiPrices data has been canonicalized to `symbol`/`timestamp` columns,
this adapter provides the same `fetch_ohlcv()` interface as the library provider.

```python
class CanonicalWikiPricesAdapter:
    """Adapter for canonicalized local Wiki Prices parquet."""

    def __init__(self, parquet_path: Path):
        self.parquet_path = Path(parquet_path)

    def fetch_ohlcv(self, symbol: str, start: str, end: str) -> pl.DataFrame:
        start_date = datetime.strptime(start, "%Y-%m-%d").date()
        end_date = datetime.strptime(end, "%Y-%m-%d").date()
        return (
            pl.scan_parquet(self.parquet_path)
            .filter(
                (pl.col("symbol") == symbol)
                & pl.col("timestamp").is_between(start_date, end_date, closed="both")
            )
            .select(
                [
                    pl.col("timestamp").cast(pl.Datetime("us")).alias("timestamp"),
                    "open",
                    "high",
                    "low",
                    "close",
                    "volume",
                    "adj_close",
                    "adj_open",
                    "adj_high",
                    "adj_low",
                    "adj_volume",
                    "ex_dividend",
                    "split_ratio",
                ]
            )
            .sort("timestamp")
            .collect()
        )

    def list_available_symbols(self) -> list[str]:
        return (
            pl.scan_parquet(self.parquet_path)
            .select(pl.col("symbol").unique().sort())
            .collect()
            .to_series()
            .to_list()
        )

    def close(self) -> None:
        """Mirror provider lifecycle API."""
        return None
```

### Load WikiPrices Provider

Try multiple paths to find WikiPrices data (local install, Docker, CI fixtures).

```python
for wiki_path in WIKI_PATHS:
    if wiki_path.exists():
        print(f"  Found: {display_path(wiki_path)}")
        try:
            wiki = WikiPricesProvider(parquet_path=wiki_path)
            wiki_path_used = wiki_path
            break
        except Exception as e:
            # File exists but failed to load - this is a real error, not silent skip
            wiki_load_errors.append((wiki_path, str(e)))
            print(f"  ERROR loading {display_path(wiki_path)}: {e}")

# If we found files but couldn't load any of them, that's a bug - fail loudly
if wiki is None and wiki_load_errors:
    error_msg = "WikiPrices files found but failed to load:\n"
    for path, err in wiki_load_errors:
        error_msg += f"  {path}: {err}\n"
    raise RuntimeError(error_msg)
```

```python
if wiki is None:
    raise RuntimeError(
        f"WikiPrices parquet not found in any of: {[str(p) for p in WIKI_PATHS]}. "
        "Materialise it via WikiPricesProvider.download(api_key=<nasdaq>) first."
    )

print(f"WikiPrices loaded from: {display_path(wiki_path_used)}")

# Fetch long-term AAPL history; the canonical local schema may need the
# adapter wrapper if the file uses asset/date instead of symbol/timestamp.
try:
    aapl_historical = wiki.fetch_ohlcv("AAPL", "1990-01-01", "2018-03-27")
except Exception as e:
    if 'unable to find column "ticker"' not in str(e):
        raise
    print("Detected canonical schema; switching to CanonicalWikiPricesAdapter.")
    wiki = CanonicalWikiPricesAdapter(wiki_path_used)
    aapl_historical = wiki.fetch_ohlcv("AAPL", "1990-01-01", "2018-03-27")

print(
    f"AAPL data: {len(aapl_historical)} rows · "
    f"{aapl_historical['timestamp'].min()} → {aapl_historical['timestamp'].max()}"
)
aapl_historical.head()
```

```python
# WikiPrices includes delisted companies — critical for avoiding survivorship bias.
available_symbols = wiki.list_available_symbols()
print(f"WikiPrices contains {len(available_symbols):,} symbols; sample: {available_symbols[:10]}")
```

---

## Section 4: Multi-Provider Fallback Strategy

For production systems, we need a robust strategy that handles:
1. API failures
2. Rate limits
3. Data gaps
4. Historical coverage

The **fallback pattern** tries providers in order until one succeeds.

```python
@dataclass
class FetchResult:
    """Result of a multi-provider fetch attempt."""

    success: bool
    data: pl.DataFrame | None
    provider_used: str | None
    providers_tried: list[str]
    error_messages: dict[str, str]
```

### Fallback Fetch

Try multiple providers in priority order; return the first successful result.

```python
def fetch_with_fallback(
    symbol: str,
    start: str,
    end: str,
    providers: list,
    provider_names: list[str],
) -> FetchResult:
    """
    Fetch data trying multiple providers in order.

    Parameters
    ----------
    symbol : str
        Ticker symbol
    start, end : str
        Date range (YYYY-MM-DD)
    providers : list
        Provider instances to try
    provider_names : list[str]
        Names for logging

    Returns
    -------
    FetchResult
        Result with data and metadata
    """
    errors = {}
    tried = []

    for provider, name in zip(providers, provider_names, strict=False):
        tried.append(name)
        try:
            data = provider.fetch_ohlcv(symbol, start, end)
            if len(data) > 0:
                return FetchResult(
                    success=True,
                    data=data,
                    provider_used=name,
                    providers_tried=tried,
                    error_messages=errors,
                )
            else:
                errors[name] = "Empty result"
        except Exception as e:
            errors[name] = str(e)

    return FetchResult(
        success=False,
        data=None,
        provider_used=None,
        providers_tried=tried,
        error_messages=errors,
    )
```

```python
# Try Yahoo first, then WikiPrices as fallback
providers = [yahoo, wiki]
provider_names = ["Yahoo Finance", "WikiPrices"]

result = fetch_with_fallback("AAPL", "2020-01-01", "2020-12-31", providers, provider_names)
if not result.success:
    raise RuntimeError(f"All providers failed: {result.error_messages}")
print(
    f"Success via {result.provider_used}: {len(result.data):,} rows; tried {result.providers_tried}"
)
```

---

## Section 5: Combining Historical and Recent Data

For 30+ year backtests, we combine:
1. **WikiPrices** (1962-2018) - includes delisted names
2. **Yahoo Finance** (2018-present) - current data

One covers a span the other does not, in both directions, so a panel that reaches from the
1960s to today has to come from both and the seam has to be somewhere.

```python
def build_complete_history(
    symbol: str,
    yahoo_provider,
    wiki_provider=None,
    start_date: str = "1990-01-01",
    end_date: str = None,
) -> pl.DataFrame:
    """Build complete OHLCV history combining WikiPrices (pre-2018) and Yahoo Finance (2018+)."""
    if end_date is None:
        end_date = AS_OF_DATE

    parts = []

    # WikiPrices cutoff
    wiki_end = "2018-03-27"

    # Part 1: Historical data from WikiPrices
    if wiki_provider and start_date < wiki_end:
        try:
            historical = wiki_provider.fetch_ohlcv(symbol, start_date, wiki_end)
            if len(historical) > 0:
                parts.append(historical)
                print(f"  WikiPrices: {len(historical)} rows ({start_date} to {wiki_end})")
        except Exception as e:
            print(f"  WikiPrices: {e}")

    # Part 2: Recent data from Yahoo Finance
    yahoo_start = "2018-03-28" if start_date < wiki_end else start_date
    try:
        recent = yahoo_provider.fetch_ohlcv(symbol, yahoo_start, end_date)
        if len(recent) > 0:
            parts.append(recent)
            print(f"  Yahoo Finance: {len(recent)} rows ({yahoo_start} to {end_date})")
    except Exception as e:
        print(f"  Yahoo Finance: {e}")

    if not parts:
        raise ValueError(f"No data found for {symbol}")

    # Standardize columns and types before concatenation
    # Both providers should have: timestamp, open, high, low, close, volume
    standard_cols = ["timestamp", "open", "high", "low", "close", "volume"]
    standardized = []
    for df in parts:
        # Select only standard columns (ensure all have same schema)
        df_std = df.select(standard_cols)
        # Normalize types: timestamp to us precision, numerics to Float64
        df_std = df_std.with_columns(
            pl.col("timestamp").cast(pl.Datetime("us")),
            pl.col("open", "high", "low", "close").cast(pl.Float64),
            pl.col("volume").cast(
                pl.Float64
            ),  # Volume can be Int64 or Float64 depending on provider
        )
        standardized.append(df_std)

    # Combine and deduplicate
    combined = pl.concat(standardized).sort("timestamp").unique("timestamp")
    print(f"  Combined: {len(combined)} rows total")

    return combined
```

```python
# Build complete AAPL history (1990-now)
aapl_complete = build_complete_history("AAPL", yahoo, wiki, "1990-01-01")
print(
    f"Combined: {len(aapl_complete):,} rows · "
    f"{aapl_complete['timestamp'].min()} → {aapl_complete['timestamp'].max()}"
)
```

---

## Section 6: Provider Data Comparison

Yahoo Finance and WikiPrices both expose a close price, but they apply different
adjustment conventions and cover different date ranges, so the two series can
diverge sharply. This section demonstrates how to:

1. Align data from multiple providers by date
2. Quantify differences (row counts, price discrepancies)
3. Identify systematic vs random variations
4. Diagnose the causes (splits, dividends, timing)

**Why this matters**: Multi-source strategies must understand when providers disagree.
Small discrepancies compound over backtests; large ones signal data errors.

```python
def compare_providers_detailed(
    symbol: str,
    start: str,
    end: str,
    provider_a,
    provider_b,
    name_a: str = "Provider A",
    name_b: str = "Provider B",
) -> dict:
    """
    Detailed comparison of two data providers for a symbol.

    Returns dict with:
    - summary: high-level stats
    - aligned: row-by-row comparison DataFrame
    - discrepancies: rows where providers disagree significantly
    """
    try:
        data_a = provider_a.fetch_ohlcv(symbol, start, end)
        data_b = provider_b.fetch_ohlcv(symbol, start, end)
    except Exception as e:
        return {"error": str(e), "summary": None, "aligned": None, "discrepancies": None}

    # Normalize timestamps to date for joining (providers may have different time components)
    data_a = data_a.with_columns(pl.col("timestamp").dt.date().alias("timestamp"))
    data_b = data_b.with_columns(pl.col("timestamp").dt.date().alias("timestamp"))

    # Inner join on date to get overlapping rows
    aligned = data_a.select(["timestamp", "open", "high", "low", "close", "volume"]).join(
        data_b.select(["timestamp", "open", "high", "low", "close", "volume"]),
        on="timestamp",
        suffix="_b",
    )

    # Calculate differences
    aligned = aligned.with_columns(
        [
            ((pl.col("close") - pl.col("close_b")) / pl.col("close_b") * 100).alias(
                "close_diff_pct"
            ),
            ((pl.col("volume") - pl.col("volume_b")) / pl.col("volume_b") * 100).alias(
                "volume_diff_pct"
            ),
        ]
    )

    discrepancies = aligned.filter(pl.col("close_diff_pct").abs() > DISCREPANCY_PCT)

    # Summary statistics
    summary = {
        "symbol": symbol,
        "period": f"{start} to {end}",
        f"{name_a}_rows": len(data_a),
        f"{name_b}_rows": len(data_b),
        "aligned_rows": len(aligned),
        "missing_in_a": len(data_b) - len(aligned),
        "missing_in_b": len(data_a) - len(aligned),
        "mean_close_diff_pct": aligned["close_diff_pct"].mean() if len(aligned) > 0 else None,
        "max_close_diff_pct": aligned["close_diff_pct"].abs().max() if len(aligned) > 0 else None,
        "discrepancy_days": len(discrepancies),
        "exact_matches": len(aligned.filter(pl.col("close_diff_pct").abs() < EXACT_MATCH_PCT)),
    }

    return {"summary": summary, "aligned": aligned, "discrepancies": discrepancies}
```

```python
comparison_result = compare_providers_detailed(
    COMPARE_SYMBOL,
    COMPARE_START,
    COMPARE_END,
    yahoo,
    wiki,
    "Yahoo",
    "WikiPrices",
)
if comparison_result.get("error"):
    raise RuntimeError(f"Comparison failed: {comparison_result['error']}")

summary = comparison_result["summary"]
summary_df = pl.DataFrame([summary])
summary_df
```

```python
disc = comparison_result["discrepancies"]
print(
    f"Days where the two closes differ by more than {DISCREPANCY_PCT}%: "
    f"{len(disc):,} of {len(comparison_result['aligned']):,} overlapping"
)
disc.select(["timestamp", "close", "close_b", "close_diff_pct"]).head(5)
```

### Reading the comparison

The two providers quote the same exchange, so their raw prints agree. What they do not
share is an adjustment basis, and the printed statistics above show that difference
dominating everything else: the exact-match count is zero and every overlapping day
differs by roughly the same large percentage.

A constant offset across a whole year is the signature to recognise. A rounding difference
would be tiny and vary day to day; a mis-dated split would be a step, agreeing before the
date and disagreeing after. A uniform ratio means the two series are the same prices under
different retroactive adjustments, and here the reason is datable: Yahoo's adjusted close
reflects Apple's 2020 split, and the WikiPrices feed stopped in 2018 and could not.

So the number to check first in any provider diff is not the mean difference but the
*shape* of the difference over time. Align the adjustment basis before comparing, or the
comparison measures the adjustment rather than the data.

---

## Section 7: ETF Universe Performance

We visualize the 7 core ETFs defined at the start of this notebook. These represent
distinct asset classes for the rotation strategy:

| Symbol | Asset Class | Role in Portfolio |
|--------|-------------|-------------------|
| SPY | US Large Cap | Risk-on equity |
| QQQ | US Tech | High-beta growth |
| IWM | US Small Cap | Cyclical exposure |
| EFA | Intl Developed | Geographic diversification |
| EEM | Emerging Markets | Growth/risk allocation |
| TLT | Long Treasury | Flight-to-quality |
| GLD | Gold | Inflation/crisis hedge |

A rotation strategy switches between these based on momentum signals (Chapter 7).

```python
# Calculate normalized prices (start = 100)
fig = go.Figure()

for symbol, df in etf_data.items():
    # Normalize to 100 at start
    normalized = (df["close"] / df["close"][0]) * 100

    fig.add_trace(
        go.Scatter(
            x=df["timestamp"].to_list(),
            y=normalized.to_list(),
            name=symbol,
            mode="lines",
        )
    )
    # Seven series exceed the categorical palette, so identity comes from a direct
    # end-label rather than from a legend lookup against a repeated color.
    fig.add_annotation(
        x=df["timestamp"][-1],
        y=normalized[-1],
        text=f" {symbol}",
        showarrow=False,
        xanchor="left",
        font=dict(size=10),
    )

fig.update_layout(
    title="Core ETFs rebased to 100 at each series' first observation",
    xaxis_title="Date",
    yaxis_title="Normalized Price",
    height=500,
    showlegend=False,
    margin=dict(r=70),
)

fig.add_hline(y=100, line_dash="dash", line_color=COLORS["neutral"], opacity=0.5)

show_plotly_with_alt(
    fig,
    "Seven price series rebased to a hundred at their own first observation and plotted "
    "over five years, each labelled at its right-hand end, with a dashed reference line at "
    "a hundred. All seven drop sharply in the first weeks, recover together, and separate "
    "from 2022 onward. Five finish well above the reference line, one finishes on it, and "
    "one runs below it for most of the window and ends furthest down.",
)
```

```python
# Calculate performance statistics
performance_stats = []

for symbol, df in etf_data.items():
    returns = df["close"].pct_change().drop_nulls()

    total_return = (df["close"][-1] / df["close"][0] - 1) * 100
    annual_return = ((1 + total_return / 100) ** (TRADING_DAYS_PER_YEAR / len(df)) - 1) * 100
    volatility = returns.std() * np.sqrt(TRADING_DAYS_PER_YEAR) * 100
    sharpe = (annual_return - RISK_FREE_RATE) / volatility if volatility > 0 else 0

    performance_stats.append(
        {
            "symbol": symbol,
            "total_return_pct": total_return,
            "annual_return_pct": annual_return,
            "volatility_pct": volatility,
            "sharpe_ratio": sharpe,
            "trading_days": len(df),
        }
    )

performance_df = pl.DataFrame(performance_stats).sort("annual_return_pct", descending=True)
performance_df
```

---

## Section 8: Economic Data with FREDProvider

For macro regime detection and risk management, FRED (Federal Reserve Economic Data)
provides 800,000+ economic time series. Key series for trading include:

| Series | Description | Frequency |
|--------|-------------|-----------|
| VIXCLS | VIX Volatility Index | Daily |
| DGS10 | 10-Year Treasury Yield | Daily |
| T10Y2Y | Yield Curve Slope | Daily |
| UNRATE | Unemployment Rate | Monthly |
| ICSA | Initial Jobless Claims | Weekly |

**Get free API key**: https://fred.stlouisfed.org/docs/api/api_key.html

```python
if not os.getenv("FRED_API_KEY"):
    raise RuntimeError(
        "FRED_API_KEY not set. Get a free key at "
        "https://fred.stlouisfed.org/docs/api/api_key.html and export it. Only this "
        "section needs it."
    )

fred = FREDProvider()
vix = fred.fetch_ohlcv(FRED_SERIES[0], FRED_START, FRED_END)
treasury_10y = fred.fetch_ohlcv(FRED_SERIES[1], FRED_START, FRED_END)
fred.close()

vix_mean = float(vix["close"].mean())
vix_max = float(vix["close"].max())
last_yield = float(treasury_10y.filter(pl.col("close").is_not_null())["close"][-1])
print(
    f"{FRED_SERIES[0]}: {len(vix):,} obs, mean {vix_mean:.1f}, max {vix_max:.1f}. "
    f"{FRED_SERIES[1]} last value {last_yield:.2f}%"
)
vix.head()
```

## Key Takeaways

1. **One signature, several sources.** The same `fetch_ohlcv()` call reaches an equity
   provider, a historical archive and a macro archive. Treat the provider as configuration
   rather than as bespoke per-source code, and a swap costs a line.

2. **Prefer fallback to fail-fast for acquisition, but keep a source column.** Preferring
   the next provider over a missing day is right; doing it without recording which provider
   answered leaves a panel nobody can audit afterwards.

3. **Comparing two providers usually measures their adjustment conventions, not their data.**
   In the run above the two feeds agree on every raw print and disagree on every adjusted
   close by roughly the same ratio, because one of them applied a split the other's coverage
   window ends before. The exact-match count is zero and the mean difference is large, and
   neither number means the data is wrong.

4. **Read the shape of a difference, not its average.** Rounding is small and varies daily; a
   mis-dated corporate action is a step; a uniform ratio across a whole window is a different
   adjustment basis. The three call for different fixes and the mean difference cannot tell
   them apart.

5. **A stitched history needs an explicit seam.** The historical feed ends on a known date, so
   the join is a filter on that date rather than a deduplication after the fact, and the row
   count printed above is what confirms nothing was double-counted.

**Next**: `17_complete_pipeline` consumes this universe end-to-end
(ingestion → quality gate → storage → query); `18_data_management`
adds the `DataManager`/`Universe`/`HiveStorage` layer for production.

```python
# Close provider sessions
yahoo.close()
wiki.close()
print(f"   - Total rows: {len(etf_universe_df):,}")
```
![notebook output](figures/p1_1.png)