Add == and != methods between Projection (mne-tools#11147)

* add comparison of proj and test

* add entry to changelog

* simpler

* simpler as it also checks type

* try with different py:obj role

* fix dataset download in test

* fix x-ref

* fix test

doc/changes/latest.inc

@@ -42,7 +42,7 @@ Enhancements
 - Add :func:`mne.minimum_norm.apply_inverse_tfr_epochs` to apply inverse methods to time-frequency resolved epochs (:gh:`11095` by `Alex Rockhill`_)
 - Add :func:`mne.chpi.get_active_chpi` to retrieve the number of active hpi coils for each time point (:gh:`11122` by `Eduard Ort`_)
 - Add example of how to obtain time-frequency decomposition using narrow bandpass Hilbert transforms to :ref:`ex-tfr-comparison` (:gh:`11116` by `Alex Rockhill`_)
-
+- Add ``==`` and ``!=`` comparison between `mne.Projection` objects (:gh:`11147` by `Mathieu Scheltienne`_)
 
 Bugs
 ~~~~

mne/io/proj.py

@@ -18,7 +18,8 @@
                     write_float_matrix, end_block, start_block)
 from ..defaults import (_INTERPOLATION_DEFAULT, _BORDER_DEFAULT,
                         _EXTRAPOLATE_DEFAULT)
-from ..utils import logger, verbose, warn, fill_doc, _validate_type
+from ..utils import (logger, verbose, warn, fill_doc, _validate_type,
+                     object_diff)
 
 
 class Projection(dict):
@@ -70,6 +71,14 @@ def __deepcopy__(self, memodict):
                 result[k] = v  # kind, active, desc, explained_var immutable
         return result
 
+    def __eq__(self, other):
+        """Equality == method."""
+        return True if len(object_diff(self, other)) == 0 else False
+
+    def __ne__(self, other):
+        """Different != method."""
+        return not self.__eq__(other)
+
     @fill_doc
     def plot_topomap(self, info, cmap=None, sensors=True,
                      colorbar=False, res=64, size=1, show=True,

mne/io/tests/test_proj.py

@@ -0,0 +1,24 @@
+from copy import deepcopy
+
+from mne.datasets.testing import data_path, requires_testing_data
+from mne.io import read_raw_fif
+
+directory = data_path(download=False) / "MEG" / "sample"
+fname = directory / "sample_audvis_trunc_raw.fif"
+
+
+@requires_testing_data
+def test_eq_ne():
+    """Test == and != between projectors."""
+    raw = read_raw_fif(fname, preload=False)
+
+    pca1 = deepcopy(raw.info["projs"][0])
+    pca2 = deepcopy(raw.info["projs"][1])
+    car = deepcopy(raw.info["projs"][3])
+
+    assert pca1 != pca2
+    assert pca1 != car
+    assert pca2 != car
+    assert pca1 == raw.info["projs"][0]
+    assert pca2 == raw.info["projs"][1]
+    assert car == raw.info["projs"][3]