allenai · epwalsh · May 7, 2021 · Apr 9, 2021 · Apr 9, 2021 · Apr 9, 2021
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -16,6 +16,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 - Added `TaskSuite` base class and command line functionality for running [`checklist`](https://github.com/marcotcr/checklist) test suites, along with implementations for `SentimentAnalysisSuite`, `QuestionAnsweringSuite`, and `TextualEntailmentSuite`. These can be found in the `allennlp.sanity_checks.task_checklists` module.
+- Added `allennlp diff` command to compute a diff on model checkpoints, analogous to what `git diff` does on two files.
+- Added `allennlp.nn.util.load_state_dict` helper function.
 - Added a way to avoid downloading and loading pretrained weights in modules that wrap transformers
   such as the `PretrainedTransformerEmbedder` and `PretrainedTransformerMismatchedEmbedder`.
   You can do this by setting the parameter `load_weights` to `False`.

diff --git a/allennlp/commands/__init__.py b/allennlp/commands/__init__.py
@@ -8,6 +8,7 @@
 from allennlp import __version__
 from allennlp.commands.build_vocab import BuildVocab
 from allennlp.commands.cached_path import CachedPath
+from allennlp.commands.diff import Diff
 from allennlp.commands.evaluate import Evaluate
 from allennlp.commands.find_learning_rate import FindLearningRate
 from allennlp.commands.predict import Predict

diff --git a/allennlp/commands/diff.py b/allennlp/commands/diff.py
@@ -0,0 +1,259 @@
+"""
+# Examples
+
+```bash
+allennlp diff \
+    hf://roberta-large/pytorch_model.bin \
+    https://storage.googleapis.com/allennlp-public-models/transformer-qa-2020-10-03.tar.gz \
+    --strip-prefix-1 'roberta.' \
+    --strip-prefix-2 '_text_field_embedder.token_embedder_tokens.transformer_model.'
+```
+"""
+import argparse
+import logging
+from typing import Union, Dict, List, Tuple, NamedTuple, cast
+
+from overrides import overrides
+import termcolor
+import torch
+
+from allennlp.commands.subcommand import Subcommand
+from allennlp.common.file_utils import cached_path
+from allennlp.nn.util import load_state_dict
+
+
+logger = logging.getLogger(__name__)
+
+
+@Subcommand.register("diff")
+class Diff(Subcommand):
+    requires_plugins: bool = False
+
+    @overrides
+    def add_subparser(self, parser: argparse._SubParsersAction) -> argparse.ArgumentParser:
+        description = """Display a diff between two model checkpoints."""
+        long_description = (
+            description
+            + """
+        In the output, lines start with either a "+", "-", "!", or empty space " ".
+        "+" means the corresponding parameter is present in the 2nd checkpoint but not the 1st.
+        "-" means the corresponding parameter is present in the 1st checkpoint but not the 2nd.
+        "!" means the corresponding parameter is present in both, but has different weights (same shape)
+        according to the distance calculation and the '--threshold' value.
+        And " " means the corresponding parameter is considered identical in both, i.e.
+        the distance falls below the threshold.
+        The distance between two tensors is calculated as the root of the
+        mean squared difference, multiplied by the '--scale' parameter.
+        """
+        )
+        subparser = parser.add_parser(
+            self.name,
+            description=long_description,
+            help=description,
+        )
+        subparser.set_defaults(func=_diff)
+        subparser.add_argument(
+            "checkpoint1",
+            type=str,
+            help="""the URL, path, or other identifier (see '--checkpoint-type-1')
+            to the 1st PyTorch checkpoint.""",
+        )
+        subparser.add_argument(
+            "checkpoint2",
+            type=str,
+            help="""the URL, path, or other identifier (see '--checkpoint-type-2')
+            to the 2nd PyTorch checkpoint.""",
+        )
+        subparser.add_argument(
+            "--strip-prefix-1",
+            type=str,
+            help="""a prefix to remove from all of the 1st checkpoint's keys.""",
+        )
+        subparser.add_argument(
+            "--strip-prefix-2",
+            type=str,
+            help="""a prefix to remove from all of the 2nd checkpoint's keys.""",
+        )
+        subparser.add_argument(
+            "--scale",
+            type=float,
+            default=1.0,
+            help="""controls the scale of the distance calculation.""",
+        )
+        subparser.add_argument(
+            "--threshold",
+            type=float,
+            default=1e-5,
+            help="""the threshold for the distance between two tensors,
+            under which the two tensors are considered identical.""",
+        )
+8000
        return subparser
+
+
+class Keep(NamedTuple):
+    key: str
+    shape: Tuple[int, ...]
+
+    def display(self):
+        termcolor.cprint(f" {self.key}, shape = {self.shape}")
+
+
+class Insert(NamedTuple):
+    key: str
+    shape: Tuple[int, ...]
+
+    def display(self):
+        termcolor.cprint(f"+{self.key}, shape = {self.shape}", "green")
+
+
+class Remove(NamedTuple):
+    key: str
+    shape: Tuple[int, ...]
+
+    def display(self):
+        termcolor.cprint(f"-{self.key}, shape = {self.shape}", "red")
+
+
+class Modify(NamedTuple):
+    key: str
+    shape: Tuple[int, ...]
+    distance: float
+
+    def display(self):
+        termcolor.cprint(
+            f"!{self.key}, shape = {self.shape}, distance = {self.distance:.4f}", "yellow"
+        )
+
+
+class _Frontier(NamedTuple):
+    x: int
+    history: List[Union[Keep, Insert, Remove]]
+
+
+def _finalize(
+    history: List[Union[Keep, Insert, Remove]],
+    state_dict_a: Dict[str, torch.Tensor],
+    state_dict_b: Dict[str, torch.Tensor],
+    scale: float,
+    threshold: float,
+) -> List[Union[Keep, Insert, Remove, Modify]]:
+    out = cast(List[Union[Keep, Insert, Remove, Modify]], history)
+    for i, step in enumerate(out):
+        if isinstance(step, Keep):
+            a_tensor = state_dict_a[step.key]
+            b_tensor = state_dict_b[step.key]
+            with torch.no_grad():
+                dist = (scale * torch.nn.functional.mse_loss(a_tensor, b_tensor).sqrt()).item()
+            if dist > threshold:
+                out[i] = Modify(step.key, step.shape, dist)
+    return out
+
+
+def checkpoint_diff(
+    state_dict_a: Dict[str, torch.Tensor],
+    state_dict_b: Dict[str, torch.Tensor],
+    scale: float,
+    threshold: float,
+) -> List[Union[Keep, Insert, Remove, Modify]]:
+    """
+    Uses a modified version of the Myers diff algorithm to compute a representation
+    of the diff between two model state dictionaries.
+
+    The only difference is that in addition to the `Keep`, `Insert`, and `Remove`
+    operations, we add `Modify`. This corresponds to keeping a parameter
+    but changing its weights (not the shape).
+
+    Adapted from [this gist]
+    (https://gist.github.com/adamnew123456/37923cf53f51d6b9af32a539cdfa7cc4).
+    """
+    param_list_a = [(k, tuple(v.shape)) for k, v in state_dict_a.items()]
+    param_list_b = [(k, tuple(v.shape)) for k, v in state_dict_b.items()]
+
+    # This marks the farthest-right point along each diagonal in the edit
+    # graph, along with the history that got it there
+    frontier: Dict[int, _Frontier] = {1: _Frontier(0, [])}
+
+    def one(idx):
+        """
+        The algorithm Myers presents is 1-indexed; since Python isn't, we
+        need a conversion.
+        """
+        return idx - 1
+
+    a_max = len(param_list_a)
+    b_max = len(param_list_b)
+    for d in range(0, a_max + b_max + 1):
+        for k in range(-d, d + 1, 2):
+            # This determines whether our next search point will be going down
+            # in the edit graph, or to the right.
+            #
+            # The intuition for this is that we should go down if we're on the
+            # left edge (k == -d) to make sure that the left edge is fully
+            # explored.
+            #
+            # If we aren't on the top (k != d), then only go down if going down
+            # would take us to territory that hasn't sufficiently been explored
+            # yet.
+            go_down = k == -d or (k != d and frontier[k - 1].x < frontier[k + 1].x)
+
+            # Figure out the starting point of this iteration. The diagonal
+            # offsets come from the geometry of the edit grid - if you're going
+            # down, your diagonal is lower, and if you're going right, your
+            # diagonal is higher.
+            if go_down:
+                old_x, history = frontier[k + 1]
+                x = old_x
+            else:
+                old_x, history = frontier[k - 1]
+                x = old_x + 1
+
+            # We want to avoid modifying the old history, since some other step
+            # may decide to use it.
+            history = history[:]
+            y = x - k
+
+            # We start at the invalid point (0, 0) - we should only start building
+            # up history when we move off of it.
+            if 1 <= y <= b_max and go_down:
+                history.append(Insert(*param_list_b[one(y)]))
+            elif 1 <= x <= a_max:
+                history.append(Remove(*param_list_a[one(x)]))
+
+            # Chew up as many diagonal moves as we can - these correspond to common lines,
+            # and they're considered "free" by the algorithm because we want to maximize
+            # the number of these in the output.
+            while x < a_max and y < b_max and param_list_a[one(x + 1)] == param_list_b[one(y + 1)]:
+                x += 1
+                y += 1
+                history.append(Keep(*param_list_a[one(x)]))
+
+            if x >= a_max and y >= b_max:
+                # If we're here, then we've traversed through the bottom-left corner,
+                # and are done.
+                return _finalize(history, state_dict_a, state_dict_b, scale, threshold)
+            else:
+                frontier[k] = _Frontier(x, history)
+
+    assert False, "Could not find edit script"
+
+
+def _get_checkpoint_path(checkpoint: str) -> str:
+    if checkpoint.endswith(".tar.gz"):
+        return cached_path(checkpoint + "!weights.th", extract_archive=True)
+    elif ".tar.gz!" in checkpoint:
+        return cached_path(checkpoint, extract_archive=True)
+    else:
+        return cached_path(checkpoint)
+
+
+def _diff(args: argparse.Namespace):
+    checkpoint_1_path = _get_checkpoint_path(args.checkpoint1)
+    checkpoint_2_path = _get_checkpoint_path(args.checkpoint2)
+    checkpoint_1 = load_state_dict(
+        checkpoint_1_path, strip_prefix=args.strip_prefix_1, strict=False
+    )
+    checkpoint_2 = load_state_dict(
+        checkpoint_2_path, strip_prefix=args.strip_prefix_2, strict=False
+    )
+    for step in checkpoint_diff(checkpoint_1, checkpoint_2, args.scale, args.threshold):
+        step.display()
diff --git a/allennlp/models/model.py b/allennlp/models/model.py
@@ -335,7 +335,7 @@ def _load(
 
         # Load state dict. We pass `strict=False` so PyTorch doesn't raise a RuntimeError
         # if the state dict is missing keys because we handle this case below.
-        model_state = torch.load(weights_file, map_location=util.device_mapping(cuda_device))
+        model_state = util.load_state_dict(weights_file, cuda_device=cuda_device)
         missing_keys, unexpected_keys = model.load_state_dict(model_state, strict=False)
 
         # Modules might define a class variable called `authorized_missing_keys`,

diff --git a/allennlp/nn/util.py b/allennlp/nn/util.py
@@ -3,9 +3,11 @@
 """
 
 import copy
+from collections import defaultdict, OrderedDict
 import json
 import logging
-from collections import defaultdict
+from os import PathLike
+import re
 from typing import Any, Dict, List, Optional, Sequence, Tuple, TypeVar, Union
 
 import math
@@ -924,6 +926,95 @@ def inner_device_mapping(storage: torch.Storage, location) -> torch.Storage:
     return inner_device_mapping
 
 
+def load_state_dict(
+    path: Union[PathLike, str],
+    strip_prefix: Optional[str] = None,
+    ignore: Optional[List[str]] = None,
+    strict: bool = True,
+    cuda_device: int = -1,
+) -> Dict[str, torch.Tensor]:
+    """
+    Load a PyTorch model state dictionary from a checkpoint at the given `path`.
+
+    # Parameters
+
+    path : `Union[PathLike, str]`, required
+
+    strip_prefix : `Optional[str]`, optional (default = `None`)
+        A prefix to remove from all of the state dict keys.
+
+    ignore : `Optional[List[str]]`, optional (default = `None`)
+        Optional list of regular expressions. Keys that match any of these will be removed
+        from the state dict.
+
+        !!! Note
+            If `strip_prefix` is given, the regular expressions in `ignore` are matched
+            before the prefix is stripped.
+
+    strict : `bool`, optional (default = `True`)
+        If `True` (the default) and `strip_prefix` was never used or any of the regular expressions
+        in `ignore` never matched, a `ValueError` will be raised.
+
+    cuda_device : `int`, optional (default = `-1`)
+        The device to load the parameters onto. Use `-1` (the default) for CPU.
+
+    # Returns
+
+    `Dict[str, torch.Tensor]`
+        An ordered dictionary of the state.
+    """
+    state = torch.load(path, map_location=device_mapping(cuda_device))
+    out: Dict[str, torch.Tensor] = OrderedDict()
+
+    if ignore is not None and not isinstance(ignore, list):
+        # If user accidentally passed in something that is not a list - like a string,
+        # which is easy to do - the user would be confused why the resulting state dict
+        # is empty.
+        raise ValueError("'ignore' parameter should be a list")
+
+    # In 'strict' mode, we need to keep track of whether we've used `strip_prefix`
+    # and which regular expressions in `ignore` we've used.
+    strip_prefix_used: Optional[bool] = None
+    ignore_used: Optional[List[bool]] = None
+    if strict and strip_prefix is not None:
+        strip_prefix_used = False
+    if strict and ignore:
+        ignore_used = [False] * len(ignore)
+
+    for key in state.keys():
+        ignore_key = False
+        if ignore:
+            for i, pattern in enumerate(ignore):
+                if re.match(pattern, key):
+                    if ignore_used:
+                        ignore_used[i] = True
+                    logger.warning("ignoring %s from state dict", key)
+                    ignore_key = True
+                    break
+
+        if ignore_key:
+            continue
+
+        new_key = key
+
+        if strip_prefix and key.startswith(strip_prefix):
+            strip_prefix_used = True
+            new_key = key[len(strip_prefix) :]
+            if not new_key:
+                raise ValueError("'strip_prefix' resulted in an empty string for a key")
+
+        out[new_key] = state[key]
+
+    if strip_prefix_used is False:
+        raise ValueError(f"'strip_prefix' of '{strip_prefix}' was never used")
+    if ignore is not None and ignore_used is not None:
+        for pattern, used in zip(ignore, ignore_used):
+            if not used:
+                raise ValueError(f"'ignore' pattern '{pattern}' didn't have any matches")
+
+    return out
+
+
 def combine_tensors(combination: str, tensors: List[torch.Tensor]) -> torch.Tensor:
     """
     Combines a list of tensors using element-wise operations and concatenation, specified by a