[Fix] Fix pathlib.Path not being counted as Niimg-like in new_image_like

CITATION.cff

@@ -295,6 +295,9 @@ authors:
   - given-names: Matthieu
     family-names: Joulot
     website: https://github.com/MatthieuJoulot
+  - given-names: Maximilian Cosmo
+    family-names: Sitter
+    website: https://github.com/mcsitter
   - given-names: Mehdi
     family-names: Rahim
     website: https://github.com/mrahim

doc/changes/latest.rst

@@ -30,6 +30,9 @@ Fixes
 
 - Relax the :func:`~nilearn.interfaces.fmriprep.load_confounds` confounds selection on `cosine` as not all confound files contained the variables (:gh:`3816` by `Hao-Ting Wang`_).
 
+- Fix pathlib.Path not being counted as Niimg-like object in :func:`~image.new_img_like` (:gh:`3723` by `Maximilian Cosmo Sitter`_).
+
+
 Enhancements
 ------------
 

nilearn/image/image.py

@@ -751,13 +751,15 @@ def new_img_like(ref_niimg, data, affine=None, copy_header=False):
     """
     # Hand-written loading code to avoid too much memory consumption
     orig_ref_niimg = ref_niimg
+    ref_niimg = stringify_path(ref_niimg)
     is_str = isinstance(ref_niimg, str)
     has_get_data = hasattr(ref_niimg, "get_data")
     has_get_fdata = hasattr(ref_niimg, "get_fdata")
     has_iter = hasattr(ref_niimg, "__iter__")
     has_affine = hasattr(ref_niimg, "affine")
     if has_iter and not any([is_str, has_get_data, has_get_fdata]):
         ref_niimg = ref_niimg[0]
+        ref_niimg = stringify_path(ref_niimg)
         is_str = isinstance(ref_niimg, str)
         has_get_data = hasattr(ref_niimg, "get_data")
         has_get_fdata = hasattr(ref_niimg, "get_fdata")

nilearn/image/tests/test_image.py

@@ -654,6 +654,24 @@ def test_new_img_like():
     assert_array_equal(get_data(img_nifti2), get_data(img2_nifti2))
 
 
+def test_new_img_like_accepts_paths(tmp_path):
+    """Check that new_img_like can accept instances of pathlib.Path."""
+    nifti_path = tmp_path / "sample.nii"
+    assert isinstance(nifti_path, Path)
+
+    data = np.random.rand(10, 10, 10)
+    img = Nifti1Image(data, np.eye(4))
+    nibabel.save(img, nifti_path)
+
+    new_data = np.random.rand(10, 10, 10)
+    new_img = new_img_like(nifti_path, new_data)
+    assert new_img.shape == (10, 10, 10)
+
+    # Check that list of pathlib.Path also accepted
+    new_img = new_img_like([nifti_path], new_data)
+    assert new_img.shape == (10, 10, 10)
+
+
 def test_new_img_like_non_iterable_header():
     """
     Tests that when an niimg's header is not iterable