控制数据泄漏的股票特征策略留出期回测

# 16_holdout_backtest.py


```py
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# %% [markdown]
# # US Firm Characteristics: Holdout Backtest
#
# **Chapter 20 - Out-of-sample evaluation**
#
# [`15_holdout_predictions`](15_holdout_predictions.ipynb) refitted the selected
# configuration on the history before the holdout window and wrote its predictions over
# it. This notebook trades them, with the sizing and the cost assumption the rest of the
# case study used, and registers the result.
#
# Nothing is chosen here. The predictions, the allocator, the concentration, the rebalance
# cadence and the charge all arrive fixed from earlier notebooks, and the only thing this
# notebook decides is that they are applied unchanged. That is the whole design: a holdout
# result is worth something exactly to the extent that no decision was made after seeing
# it, and every knob left open here would be a decision.
#
# The comparison to validation is printed but not interpreted. One year of monthly
# decisions is twelve observations, and what can be said about a Sharpe estimated from
# twelve observations is [`17_strategy_analysis`](17_strategy_analysis.ipynb)'s subject,
# with the intervals to say it.
#
# **The window is 2016, declared in `config/setup.yaml` as `holdout_start` 2016-01-01 to
# `holdout_end` 2016-12-31.** The panel is monthly and `labels.rebalance_step` is 1, so the
# strategy takes a decision at each month end and the window holds twelve of them. That
# twelve is not incidental to the reading of this notebook; it is the sample size behind
# every number section 4 prints, and it is why the language there is about what the figures
# cannot separate rather than about what they show.
#
# Why the holdout is one year rather than five is a consequence of the walk-forward scheme
# rather than a preference. `evaluation` declares ten splits with a ten-year training window
# and a one-year validation window each, rolling forward across a panel that begins in 1996.
# Widening the holdout takes those years away from the ten folds that select the model, and
# on a monthly panel a fold cannot be shortened much before its validation year stops
# containing enough cross-sections to rank anything. The cost of the choice is precisely the
# sampling error this notebook keeps naming.
#
# **Prerequisites:** [`15_holdout_predictions`](15_holdout_predictions.ipynb).
#
# **Scope:** one backtest. No selection, no comparison beyond a printed pair.

# %%
"""US Firm Characteristics: Holdout Backtest."""

import json
import sqlite3
import warnings

import polars as pl

warnings.filterwarnings("ignore")

from case_studies.research import open_study
from case_studies.research.holdout import build_holdout_training_spec
from case_studies.utils.backtest_loaders import get_backtest_config, load_backtest_prices_for
from case_studies.utils.backtest_presets import (
    ensure_backtest_spec,
    strategy_view,
)
from case_studies.utils.backtest_runner import resolved_allow_short_selling, run_backtest
from case_studies.utils.conformal import (
    compute_holdout_conformal_widths,
    ensure_conformal_calibration_identity,
    holdout_conformal_embargo_steps,
)
from case_studies.utils.registry import backtest_run_status, read_predictions
from case_studies.utils.strategy_analysis import resolve_solvent_carrier
from utils.paths import get_case_study_dir

# %% tags=["parameters"]
CASE_STUDY_ID = "us_firm_characteristics"
EXECUTION_TIER = "canonical"
WORKSPACE: str = ""
MAX_SYMBOLS = 0
# Whether a holdout backtest of a DIFFERENT strategy may be superseded by this run. Off by
# default, and the same switch `15_holdout_predictions` uses for the model side.
REPLACE_HOLDOUT = False

# %%
study = open_study(CASE_STUDY_ID, execution_tier=EXECUTION_TIER, workspace=WORKSPACE or None)
CASE_DIR = get_case_study_dir(CASE_STUDY_ID)
bt_config = get_backtest_config(CASE_STUDY_ID)


def _registered_holdout_backtests(case_dir, prediction_hash):
    """The backtest hashes already registered against one holdout prediction set."""
    with sqlite3.connect(str(case_dir / "run_log" / "registry.db")) as conn:
        rows = conn.execute(
            "SELECT backtest_hash FROM backtest_runs WHERE prediction_hash = ? "
            "ORDER BY backtest_hash",
            (prediction_hash,),
        ).fetchall()
    return [{"backtest_hash": backtest_hash} for (backtest_hash,) in rows]


def _delete_holdout_backtest(case_dir, backtest_hash):
    """Remove one registered holdout backtest and the rows derived from it.

    Same rule as `15_holdout_predictions`' replacement of a superseded generation: a
    holdout result that has been observed and then left readable beside its replacement is
    still a number someone can quote.
    """
    with sqlite3.connect(str(case_dir / "run_log" / "registry.db")) as conn:
        conn.execute(
            "DELETE FROM backtest_paired_metrics WHERE challenger_hash = ? OR benchmark_hash = ?",
            (backtest_hash, backtest_hash),
        )
        conn.execute("DELETE FROM backtest_metrics WHERE backtest_hash = ?", (backtest_hash,))
        conn.execute("DELETE FROM backtest_runs WHERE backtest_hash = ?", (backtest_hash,))


# %% [markdown]
# ## 1. The configuration, and the predictions it produced on the holdout
#
# The selected configuration is resolved the same way [`14_costs`](14_costs.ipynb) and
# [`15_holdout_predictions`](15_holdout_predictions.ipynb) resolve it, so all three run
# the same configuration by construction rather than by a hash copied between them.
#
# Which holdout prediction set belongs to it is derived rather than searched for. Re-deriving the
# holdout training specification reproduces the training identity 15 registered - the derivation is
# deterministic and the identity covers it - so the prediction set is looked up by that identity and
# the selected configuration's checkpoint. A search over holdout prediction sets would have to guess
# which one belonged to this configuration, and this case study's registry holds an older one that
# does not.

# %%
carrier = resolve_solvent_carrier(CASE_STUDY_ID)
LABEL = carrier["label"]
validation_prediction_record = study.results.open(carrier["val_prediction_hash"]).registry_record()

holdout_spec = build_holdout_training_spec(
    study,
    study.results.open(carrier["training_hash"]).spec(),
    timeline=(
        pl.read_parquet(study.root / "labels" / f"{LABEL}.parquet")
        .get_column("timestamp")
        .unique()
        .sort()
        .to_list()
    ),
    case_study=CASE_STUDY_ID,
)

# %%
from case_studies.utils.registry import training_hash_from_spec

holdout_training_hash = training_hash_from_spec(holdout_spec)
with sqlite3.connect(str(CASE_DIR / "run_log" / "registry.db")) as conn:
    match = conn.execute(
        """
        SELECT prediction_hash FROM prediction_sets
        WHERE split = 'holdout' AND training_hash = ?
          AND checkpoint_kind IS ? AND checkpoint_value IS ?
        """,
        (
            holdout_training_hash,
            validation_prediction_record["checkpoint_kind"],
            validation_prediction_record["checkpoint_value"],
        ),
    ).fetchone()
if match is None:
    raise RuntimeError(
        f"No holdout prediction set for training {holdout_training_hash}. Run "
        "15_holdout_predictions first; this notebook does not fit."
    )
HOLDOUT_PREDICTION_HASH = match[0]

print(f"Carrier:            {carrier['val_backtest_hash']}  {carrier['config_name']} ({LABEL})")
print(f"Holdout training:   {holdout_training_hash}")
print(f"Holdout prediction: {HOLDOUT_PREDICTION_HASH}")

# %% [markdown]
# ## 2. Calibrating the allocator on validation residuals only
#
# This configuration sizes positions by a conformal width, and a width is calibrated from the
# errors the model has already made. On the holdout there are none to use: an error is
# only usable once the return it measures has been realised, and every holdout return
# realises inside the window being evaluated. So the widths come from the validation
# residuals of the validation prediction set, which is what the allocator would have had
# standing at the start of the window.
#
# A conformal width is an interval around a prediction, sized so that a stated fraction of
# past errors fell inside an interval built the same way. The `alpha` in the allocator's
# parameters is the fraction allowed to fall outside, so a smaller alpha buys a wider
# interval. The width is therefore a statement about how wrong this model has been on
# this name, and nothing about how large the return is expected to be.
#
# That distinction is what makes `conformal_weighted` a different strategy from
# `score_weighted` rather than a rescaling of it. `score_weighted` puts more capital where
# the predicted return is larger. `conformal_weighted` puts more capital where the
# prediction has been more reliable. The two agree only when the model's confidence happens
# to track its predictions, and on this panel there is no reason it should: a firm's
# characteristics can imply a large expected return while that firm's own residual history
# is short or dispersed.
#
# A width is not purely firm-specific, and the exception matters on a panel with a firm
# axis this wide. `min_calibration_n` is the number of validation residuals a name needs
# before it gets a width of its own, and `compute_holdout_conformal_widths` does drop such
# a name from its per-symbol table. It is **not left without a width**: the symbols that
# fall out are recovered by an anti-join against the holdout's own symbol set and given one
# quantile taken over all the embargoed validation residuals together, recorded in the
# artifact as `calibration_scope = "pooled"` rather than `"symbol"`. So a thinly covered
# firm is sized on the family's typical reliability rather than excluded, and every
# selected name carries a width. `compute_conformal_weights` depends on that: it raises
# rather than proceeding if any selected asset has no width.
#
# What reaches the portfolio is narrower still. `compute_conformal_weights` normalizes
# `1 / width` within each leg at each timestamp, so only the cross-sectional dispersion of
# the widths inside that month's long and short sides changes any weight. A month in which
# every selected name carries a similar width, including one where most of them carry the
# pooled fallback, allocates close to equally, and the level of the widths never reaches
# the weights at all.
#
# No validation observation is dropped at the boundary, and the reason is the label rather
# than a choice. The embargo exists because a residual observed at `t` measures a return
# realising over `(t, t+h]`, so with `h > 0` the last residuals of the validation span
# reach into the holdout window and would size holdout positions with holdout price
# information. This panel declares `h = 0D` - each row is dated by the month the return
# was earned - so the outcome is already realised at the observation and nothing reaches
# forward. The step count comes from the reviewed table in `conformal.py`, which records
# the label horizon; it carried 1 for these labels, which discarded the last month of
# calibration against a leak the label cannot have.
#
# The embargo is derived here because the backtest identity below is built from it. The
# widths themselves are NOT written here: writing them replaces the artifact the already
# registered run was sized by, and the replacement guard in section 3 can still refuse this
# run afterwards. That order left the registered holdout pointing at a calibration that no
# longer existed, so the write moved below the guard and nothing is overwritten until this
# run is cleared to register.

# %% tags=["results"]
allocation = strategy_view(json.loads(carrier["spec_json"])).get("allocation") or {}
NEEDS_CALIBRATION = allocation.get("method") == "conformal_weighted"
embargo_steps = holdout_conformal_embargo_steps(CASE_STUDY_ID, LABEL) if NEEDS_CALIBRATION else 0
if NEEDS_CALIBRATION:
    print(f"Conformal carrier: embargo {embargo_steps} observation(s), widths written below.")
else:
    print(f"Allocator {allocation.get('method', 'equal_weight')!r} needs no calibration.")

# %% [markdown]
# ## 3. The backtest
#
# The strategy specification is the selected configuration's own, re-pointed at the holdout
# prediction set and the holdout price window. Nothing else about it changes - the commission and
# slippage are the levels `setup.yaml` declares, the same ones every validation number in this case
# study was net of, and the same ones sitting inside the swept grid in [`14_costs`](14_costs.ipynb).
#
# What that specification does to a prediction, in order, since this notebook is where a
# reader arrives wanting the whole strategy in one place rather than assembled from four
# earlier ones. At each month end the model scores every firm in the cross-section.
# `setup.yaml` declares `entry_logic: rank_top_k_long_bottom_k_short`, so the strategy goes
# **long the top `k` and short the bottom `k`**, drawn from the grid
# `backtest.sweep.top_k_grid` declares as 5, 10, 20 and 50. The book therefore holds up to
# `2k` names, not `k`, and the two sides are kept disjoint: `build_target_weights` caps the
# effective `k` at half the cross-section, leaving the median firm unselected on an odd
# universe. The allocator sets the weights within each leg, by score or by conformal width,
# and normalizes the legs separately. The result is one weight vector for the month, and
# the backtest earns each name's realised forward return over that month.
#
# **`min_weight_change` and `min_trade_value` do not act here**, and the reason is worth
# stating because `setup.yaml` declares both under `backtest.rebalance.default`. They are
# engine-path settings: a threshold below which a change in target weight is not turned
# into an order. This case study runs `_run_vectorized`, which is handed the target weights
# and computes return and turnover from them directly, and is never handed either
# threshold. So no trade here is suppressed for being small, and the turnover the cost
# sweep in [`14_costs`](14_costs.ipynb) charges is the full month-to-month weight change.
# The declarations stay because the same file drives the engine-path case studies where
# they do act, which is the same reason `MAX_SYMBOLS` survives in
# [`13_risk_management`](13_risk_management.ipynb).
#
# The run registers under `stage='holdout'`, which the registry derives from the
# prediction set's split rather than from anything asserted here.
#
# One thing the hash does not cover: a conformal configuration reads its widths from an
# artifact beside the prediction set, and the backtest identity covers the allocator's declared
# parameters but not the calibration those widths were built from. Change the embargo and
# the hash does not move, so a registered run would be served back against inputs that no
# longer exist - and the registry refuses the overwrite rather than accepting either, which
# is how that state announces itself. Re-calibrating this case study's holdout therefore
# means deleting the registered run first, the same rule section 3 of
# [`15_holdout_predictions`](15_holdout_predictions.ipynb) applies to a superseded
# generation.

# %% tags=["results"]
prices = load_backtest_prices_for(CASE_STUDY_ID, LABEL, split="holdout", max_symbols=MAX_SYMBOLS)
predictions = read_predictions(CASE_STUDY_ID, HOLDOUT_PREDICTION_HASH)
print(f"Prices: {len(prices):,} rows, {prices['symbol'].n_unique():,} assets")
print(f"Predictions: {predictions.height:,} rows, {predictions['timestamp'].n_unique()} dates")

spec = ensure_backtest_spec(
    CASE_STUDY_ID,
    bt_config,
    json.loads(carrier["spec_json"]),
    prices=prices,
    prediction_hash=HOLDOUT_PREDICTION_HASH,
    initial_cash=bt_config.initial_cash,
)
spec["chapter"] = "ch20"
# The embargo goes into the specification here, before anything hashes it. The widths are
# an input to this backtest and the embargo decides them, so two embargoes are two results
# and must not share an identity - which they did: changing it left the hash where it was
# and the registry refused to overwrite the registered run rather than accept either.
# Recorded by the notebook rather than inside `run_backtest`, because callers elsewhere
# construct and hash their own resolved specifications and compare the runner's answer to
# them; a runner that added a key after that would make those comparisons fail.
if NEEDS_CALIBRATION:
    spec = ensure_conformal_calibration_identity(spec, holdout_embargo_steps=embargo_steps)

# The window carries one backtest at a time, for the same reason `15` lets it carry one
# prediction generation at a time. `15`'s guard is on the model - the training identity and
# the checkpoint - and it cannot see this one: a changed allocator, overlay, cost level or
# calibration produces the same holdout predictions and a different result from them.
#
# The test is the backtest hash, not a field-by-field comparison. Every input that changes
# the result is in that hash by construction, and a guard naming fields instead has to be
# right about all of them - it was written first as a `strategy` comparison and missed the
# cost configuration and the calibration identity, both of which sit outside that block.
#
# The hash is resolved before anything runs, so nothing is evaluated on the holdout before
# the question is answered. It comes from `backtest_run_status`, which is the call the
# runner itself makes to decide whether a spec is already registered - asking it is the
# only way to be sure the guard and the runner agree about identity, and reconstructing the
# hash from parts here did not: it predicted f23ff90cf518 against the runner's b2acfd5420c8.
# The run asserts the two still agree afterwards, because a guard that had quietly stopped
# predicting the hash would let everything through while looking correct.
spec["backtest_config"]["account"]["allow_short_selling"] = resolved_allow_short_selling(spec, None)
prospective_hash = backtest_run_status(CASE_STUDY_ID, HOLDOUT_PREDICTION_HASH, spec).backtest_hash
superseded_backtests = sorted(
    {
        row["backtest_hash"]
        for row in _registered_holdout_backtests(CASE_DIR, HOLDOUT_PREDICTION_HASH)
    }
    - {prospective_hash}
)
if superseded_backtests and not REPLACE_HOLDOUT:
    raise RuntimeError(
        "the holdout window already carries a backtest of a different configuration: "
        + ", ".join(superseded_backtests)
        + f". This run would register {prospective_hash} and has not run. Set "
        "REPLACE_HOLDOUT=True to discard the earlier one, or leave the selection where it was."
    )
for backtest_hash in superseded_backtests:
    print(f"REPLACING holdout backtest {backtest_hash}")
    _delete_holdout_backtest(CASE_DIR, backtest_hash)

# The guard has passed, so this run will register and the widths it is sized by are the
# ones that belong beside this prediction set.
if NEEDS_CALIBRATION:
    widths = compute_holdout_conformal_widths(
        CASE_STUDY_ID,
        carrier["val_prediction_hash"],
        HOLDOUT_PREDICTION_HASH,
        alpha=float(allocation.get("alpha", 0.2)),
        min_calibration_n=int(allocation["min_calibration_n"]),
        embargo_steps=embargo_steps,
        write=True,
    )
    print(
        f"Conformal widths: {widths.height:,} rows over "
        f"{widths['symbol'].n_unique():,} names, embargo {embargo_steps} observation(s)"
    )
    print(f"  calibration_n: median {widths['calibration_n'].median():.0f}")

result = run_backtest(
    CASE_STUDY_ID,
    HOLDOUT_PREDICTION_HASH,
    spec,
    prices=prices,
    predictions=predictions,
    label=LABEL,
    register=True,
    initial_cash=bt_config.initial_cash,
    calendar=bt_config.calendar,
)
if result.backtest_hash != prospective_hash:
    raise RuntimeError(
        f"the guard predicted {prospective_hash} and the runner registered "
        f"{result.backtest_hash}. The guard decides what may run on the holdout, so a guard "
        "that no longer reproduces the runner's identity is not a smaller problem than the "
        "one it was written for."
    )
print(f"Holdout backtest: {result.backtest_hash}")

# %% [markdown]
# ## 4. What it came out at
#
# The two numbers below are one strategy measured on two disjoint periods, and the gap
# between them is not an estimate of decay. The validation figure is the maximum of a
# ranking over more than a thousand backtests, so it carries the selection; the holdout
# figure is one measurement of twelve monthly returns, so it carries the sampling error of
# twelve observations. Both facts push the pair apart on their own, before any real change
# in the strategy's edge. [`17_strategy_analysis`](17_strategy_analysis.ipynb) is where
# they are given intervals and a paired comparison.
#
# Four statistics are printed and they do not all mean the same amount here. CAGR is the
# constant annual growth rate that would have produced the window's total return, and over
# a window that is exactly one year it is just that return, so it adds no information the
# return does not already carry and is reported for comparability with the other case
# studies. Sharpe is the mean monthly return divided by its standard deviation, annualised
# at the `periods_per_year` of 12 that `setup.yaml` declares; estimated from twelve
# observations its standard error is large enough that the interval around it will cover a
# wide range of values, which is the whole reason it is not interpreted here.
#
# Maximum drawdown and win rate are the two that behave differently, in opposite
# directions. Maximum drawdown is the largest peak-to-trough fall in the equity curve, and
# it is a single realised extreme rather than an average, so it is the one figure here a
# short window does not shrink the meaning of: the strategy either did or did not give that
# much back. Win rate is the fraction of the twelve months that were positive, so it moves
# in steps of one twelfth and cannot distinguish a strategy that wins narrowly from one
# that wins by a wide margin. Read it as a count, not as a probability.

# %% tags=["results"]
metrics = result.metrics
# The selected configuration's own registered Sharpe, not the resolver's. `resolve_solvent_carrier`
# reports the common-support figure, which re-ranks the conformal field on the timestamps every
# candidate covers; that is the right number for choosing between candidates and the wrong one to
# set beside a holdout measured over its own full window. Both are printed, so neither has to be
# inferred from the other.
with sqlite3.connect(str(CASE_DIR / "run_log" / "registry.db")) as conn:
    carrier_sharpe, carrier_periods = conn.execute(
        "SELECT sharpe, n_periods FROM backtest_metrics WHERE backtest_hash = ?",
        (carrier["val_backtest_hash"],),
    ).fetchone()

print(f"Validation Sharpe over its {int(carrier_periods)} months:  {carrier_sharpe:.3f}")
print(f"  the same run re-ranked on common support: {carrier['val_sharpe']:.3f}")
print(
    f"Holdout Sharpe over {int(metrics['n_periods'])} months:        "
    f"{metrics.get('sharpe', float('nan')):.3f}"
)
print(
    f"Holdout: CAGR {metrics.get('cagr', float('nan')):.1%}, "
    f"max drawdown {metrics.get('max_drawdown', float('nan')):.2%}, "
    f"win rate {metrics.get('win_rate', float('nan')):.0%}"
)
# No trade or turnover figure is reported. The vectorized rebalance path this case study
# runs does not record one - `num_trades` is NULL for every backtest in this registry,
# holdout and validation alike - and a zero standing in for an unrecorded count reads as a
# strategy that never traded.

# %% [markdown]
# ## What this notebook establishes, and what it does not
#
# It establishes a return series for the selected configuration over a period no choice in
# this case study was made on. That is the only thing a holdout can give, and it is worth
# less than it looks: one year of monthly rebalances is twelve observations, which is too
# few to separate a strategy that decayed from one that had an ordinary year.
#
# It does not establish that this configuration was the right one to carry here. The
# selection that brought it was made on validation, over a pool large enough that its
# maximum is optimistic by construction, and this notebook inherits that pool without
# correcting for it. The deflation is [`17_strategy_analysis`](17_strategy_analysis.ipynb)'s.
#
# The holdout stays re-runnable. If the selection changes, this generation is deleted and
# another is produced; it is not a resource that has been spent.
#
# **Next:** [`17_strategy_analysis`](17_strategy_analysis.ipynb).

```