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Evaluate markers under environment with empty "extra" #550

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4 changes: 3 additions & 1 deletion CHANGELOG.rst
Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,9 @@ Changelog
*unreleased*
~~~~~~~~~~~~

No unreleased changes.
* ``Marker.evaluate`` will now assume evaluation environment with empty ``extra``.
Evaluating markers like ``"extra == 'xyz'"`` without passing any extra in the
``environment`` will no longer raise an exception.

21.3 - 2021-11-17
~~~~~~~~~~~~~~~~~
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11 changes: 0 additions & 11 deletions docs/markers.rst
Original file line number Diff line number Diff line change
Expand Up @@ -34,17 +34,6 @@ Usage
>>> # Markers can be also used with extras, to pull in dependencies if
>>> # a certain extra is being installed
>>> extra = Marker('extra == "bar"')
>>> # Evaluating an extra marker with no environment is an error
>>> try:
... extra.evaluate()
... except UndefinedEnvironmentName:
... pass
>>> extra_environment = {'extra': ''}
>>> extra.evaluate(environment=extra_environment)
False
>>> extra_environment['extra'] = 'bar'
>>> extra.evaluate(environment=extra_environment)
True
>>> # You can do simple comparisons between marker objects:
>>> Marker("python_version > '3.6'") == Marker("python_version > '3.6'")
True
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23 changes: 3 additions & 20 deletions packaging/markers.py
Original file line number Diff line number Diff line change
Expand Up @@ -215,24 +215,6 @@ def _eval_op(lhs: str, op: Op, rhs: str) -> bool:
return oper(lhs, rhs)


class Undefined:
pass


_undefined = Undefined()


def _get_env(environment: Dict[str, str], name: str) -> str:
value: Union[str, Undefined] = environment.get(name, _undefined)

if isinstance(value, Undefined):
raise UndefinedEnvironmentName(
f"{name!r} does not exist in evaluation environment."
)

return value
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def _normalize(*values: str, key: str) -> Tuple[str, ...]:
# PEP 685 – Comparison of extra names for optional distribution dependencies
# https://peps.python.org/pep-0685/
Expand All @@ -258,12 +240,12 @@ def _evaluate_markers(markers: List[Any], environment: Dict[str, str]) -> bool:

if isinstance(lhs, Variable):
environment_key = lhs.value
lhs_value = _get_env(environment, environment_key)
lhs_value = environment[environment_key]
rhs_value = rhs.value
else:
lhs_value = lhs.value
environment_key = rhs.value
rhs_value = _get_env(environment, environment_key)
rhs_value = environment[environment_key]

lhs_value, rhs_value = _normalize(lhs_value, rhs_value, key=environment_key)
groups[-1].append(_eval_op(lhs_value, op, rhs_value))
Expand All @@ -287,6 +269,7 @@ def default_environment() -> Dict[str, str]:
iver = format_full_version(sys.implementation.version)
implementation_name = sys.implementation.name
return {
"extra": "",
"implementation_name": implementation_name,
"implementation_version": iver,
"os_name": os.name,
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9 changes: 3 additions & 6 deletions tests/test_markers.py
Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,6 @@
Marker,
Node,
UndefinedComparison,
UndefinedEnvironmentName,
default_environment,
format_full_version,
)
Expand Down Expand Up @@ -110,6 +109,7 @@ def test_matches_expected(self):
)

assert environment == {
"extra": "",
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Since default_environment is part of the public API (pending documentation #503), I wonder if we should avoid adding extra to it.

"implementation_name": sys.implementation.name,
"implementation_version": iver,
"os_name": os.name,
Expand Down Expand Up @@ -253,11 +253,8 @@ def test_compare_markers_to_other_objects(self):
# Markers should not be comparable to other kinds of objects.
assert Marker("os_name == 'nt'") != "os_name == 'nt'"

def test_extra_with_no_extra_in_environment(self):
# We can't evaluate an extra if no extra is passed into the environment
m = Marker("extra == 'security'")
with pytest.raises(UndefinedEnvironmentName):
m.evaluate()
def test_environment_assumes_empty_extra(self):
assert Marker('extra == "im_valid"').evaluate() is False

@pytest.mark.parametrize(
("marker_string", "environment", "expected"),
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