What causes "Cannot restore Marker from {state!r}" in pypa/pip?

Do not rely on long-lived Marker pickles; store the marker string and rebuild with Marker(...) on load.

pypa/pip · error · TypeError

Cannot restore Marker from

Error message

Cannot restore Marker from {state!r}

What it means

Raised by Marker.__setstate__ (markers.py:466-468) for the stable 26.2+ pickle format where state is the marker expression string. If that string cannot be re-parsed by _parse_marker (ParserSyntaxError), unpickling raises TypeError('Cannot restore Marker from ...'). The original parse error is chained via 'from exc'.

Solutions

Do not rely on long-lived Marker pickles; store the marker string and rebuild with Marker(...) on load.
Recreate the pickle with the current packaging version.

Example fix

# before (fragile)
import pickle
m = pickle.loads(blob)  # corrupted string
# after (robust)
from packaging.markers import Marker
m = Marker(stored_marker_string)

Defensive patterns

Strategy: validation

Validate before calling

from packaging.markers import Marker
from packaging._tokenizer import ParserSyntaxError

def marker_string_reparses(s: str) -> bool:
    try:
        Marker(s)
    except Exception:
        return False
    return True

Try / catch

import pickle
from packaging.markers import Marker

obj = pickle.loads(blob)
if not isinstance(obj, Marker):
    # recreate from the stored string instead of trusting the pickle
    ...

Prevention

Prefer storing the marker expression string and rebuilding via Marker(...) over persisting Marker pickles.
Validate stored marker strings parse cleanly before pickling them.

When it happens

Trigger: Unpickling a Marker whose stored expression string is malformed — e.g. a hand-crafted pickle, a string corrupted in transit/storage, or a marker string valid under an older packaging grammar that the current parser rejects.

Common situations: Loading pickled requirement/dependency objects across packaging versions; a serialization layer that rewrote or truncated the marker string before pickling.

Related errors

AI-assisted analysis of pypa/pip@f399c37189 (2026-08-08). Data as JSON: /api/errors/5e9b4171bf9484c3. Report an issue: GitHub.

Appendix: source

Thrown at src/pip/_vendor/packaging/markers.py:468

    def __eq__(self, other: object) -> bool:
        if not isinstance(other, Marker):
            return NotImplemented

        return str(self) == str(other)

    def __getstate__(self) -> str:
        # Return the marker expression string for compactness and stability.
        # Internal Node objects are excluded; the string is re-parsed on load.
        return str(self)

    def __setstate__(self, state: object) -> None:
        if isinstance(state, str):
            # New format (26.2+): just the marker expression string.
            try:
                self._markers = _normalize_extra_values(_parse_marker(state))
            except ParserSyntaxError as exc:
                raise TypeError(f"Cannot restore Marker from {state!r}") from exc
            return
        if isinstance(state, dict) and "_markers" in state:
            # Old format (packaging <= 26.1, no __slots__): plain __dict__.
            markers = state["_markers"]
            if isinstance(markers, list):
                self._markers = markers
                return
        if isinstance(state, tuple) and len(state) == 2:
            # Old format (packaging <= 26.1, __slots__): (None, {slot: value}).
            _, slot_dict = state
            if isinstance(slot_dict, dict) and "_markers" in slot_dict:
                markers = slot_dict["_markers"]
                if isinstance(markers, list):
                    self._markers = markers
                    return
        raise TypeError(f"Cannot restore Marker from {state!r}")

    def __and__(self, other: Marker) -> Marker:

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