Repository: ecmwf/earthkit-data (python)

Issue:
Weird behaviour of indices() function
### What happened?

When I create a first FieldList object and call the fl.indices() function, I get a nice dictionary of metadata like this one:
```
{'class': ['od'], 'stream': ['enfo'], 'levtype': ['sfc'], 'type': ['pf'], 'expver': ['0001'], 'date': [20231128], 'time': [1200], 'domain': ['g'], 'number': [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 'param': ['2t']}
```
but when I operate on the object, by doing `fl_new = fl.sel(param='2t')` or `fl_new = ekds.order_by("number", "stepRange")`, then I get the following error when calling fl_new.indices():
```
TypeError: 'list' object is not callable
```
Do you know what is the issue?

### What are the steps to reproduce the bug?

See above.

### Version

feature/tensor

### Platform (OS and architecture)

macOS

### Relevant log output

_No response_

### Accompanying data

_No response_

### Organisation

_No response_

Pull request description:
Fix indices() on fieldlist filtered with sel()
Fixes #264 

Patch:
diff --git a/.gitignore b/.gitignore
index 8456551..fe6a017 100644
--- a/.gitignore
+++ b/.gitignore
@@ -359,3 +359,5 @@ notebooks/data/*/
 
 # local code
 _dev
+
+test.db
diff --git a/earthkit/data/core/fieldlist.py b/earthkit/data/core/fieldlist.py
index b44c1db..03ed322 100644
--- a/earthkit/data/core/fieldlist.py
+++ b/earthkit/data/core/fieldlist.py
@@ -537,7 +537,7 @@ class Field(Base):
 class FieldList(Index):
     r"""Represents a list of :obj:`Field` \s."""
 
-    _indices = {}
+    _md_indices = {}
 
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
@@ -622,12 +622,12 @@ class FieldList(Index):
         used in :obj:`indices`.
 
         """
-        if not self._indices:
-            self._indices = self._find_all_index_dict()
+        if not self._md_indices:
+            self._md_indices = self._find_all_index_dict()
         if squeeze:
-            return {k: v for k, v in self._indices.items() if len(v) > 1}
+            return {k: v for k, v in self._md_indices.items() if len(v) > 1}
         else:
-            return self._indices
+            return self._md_indices
 
     def index(self, key):
         r"""Return the unique, sorted values of the specified metadata ``key`` from all the fields.
@@ -659,8 +659,8 @@ class FieldList(Index):
         if key in self.indices():
             return self.indices()[key]
 
-        self._indices[key] = self._find_index_values(key)
-        return self._indices[key]
+        self._md_indices[key] = self._find_index_values(key)
+        return self._md_indices[key]
 
     def to_numpy(self, **kwargs):
         r"""Return the field values as an ndarray. It is formed as the array of the
diff --git a/earthkit/data/core/index.py b/earthkit/data/core/index.py
index 455d909..76c8d8e 100644
--- a/earthkit/data/core/index.py
+++ b/earthkit/data/core/index.py
@@ -550,8 +550,8 @@ class Index(Source):
 
 class MaskIndex(Index):
     def __init__(self, index, indices):
-        self.index = index
-        self.indices = list(indices)
+        self._index = index
+        self._indices = list(indices)
         # super().__init__(
         #     *self.index._init_args,
         #     order_by=self.index._init_order_by,
@@ -559,19 +559,19 @@ class MaskIndex(Index):
         # )
 
     def _getitem(self, n):
-        n = self.indices[n]
-        return self.index[n]
+        n = self._indices[n]
+        return self._index[n]
 
     def __len__(self):
-        return len(self.indices)
+        return len(self._indices)
 
     def __repr__(self):
-        return "MaskIndex(%r,%s)" % (self.index, self.indices)
+        return "MaskIndex(%r,%s)" % (self._index, self._indices)
 
 
 class MultiIndex(Index):
     def __init__(self, indexes, *args, **kwargs):
-        self.indexes = list(indexes)
+        self._indexes = list(indexes)
         super().__init__(*args, **kwargs)
         # self.indexes = list(i for i in indexes if len(i))
         # TODO: propagate  index._init_args, index._init_order_by, index._init_kwargs, for each i in indexes?
@@ -579,36 +579,36 @@ class MultiIndex(Index):
     def sel(self, *args, **kwargs):
         if not args and not kwargs:
             return self
-        return self.__class__(i.sel(*args, **kwargs) for i in self.indexes)
+        return self.__class__(i.sel(*args, **kwargs) for i in self._indexes)
 
     def _getitem(self, n):
         k = 0
-        while n >= len(self.indexes[k]):
-            n -= len(self.indexes[k])
+        while n >= len(self._indexes[k]):
+            n -= len(self._indexes[k])
             k += 1
-        return self.indexes[k][n]
+        return self._indexes[k][n]
 
     def __len__(self):
-        return sum(len(i) for i in self.indexes)
+        return sum(len(i) for i in self._indexes)
 
     def graph(self, depth=0):
         print(" " * depth, self.__class__.__name__)
-        for s in self.indexes:
+        for s in self._indexes:
             s.graph(depth + 3)
 
     def __repr__(self):
         return "%s(%s)" % (
             self.__class__.__name__,
-            ",".join(repr(i) for i in self.indexes),
+            ",".join(repr(i) for i in self._indexes),
         )
 
 
 class ForwardingIndex(Index):
     def __init__(self, index):
-        self.index = index
+        self._index = index
 
     def __len__(self):
-        return len(self.index)
+        return len(self._index)
 
 
 class ScaledField:
@@ -635,7 +635,7 @@ class FullIndex(Index):
     def __init__(self, index, *coords):
         import numpy as np
 
-        self.index = index
+        self._index = index
 
         # Pass1, unique values
         unique = index.unique_values(*coords)
@@ -663,4 +663,4 @@ class FullIndex(Index):
 
     def _getitem(self, n):
         assert self.holes[n], f"Attempting to access hole {n}"
-        return self.index[sum(self.holes[:n])]
+        return self._index[sum(self.holes[:n])]
diff --git a/earthkit/data/readers/netcdf.py b/earthkit/data/readers/netcdf.py
index 4cd0062..acd1ba9 100644
--- a/earthkit/data/readers/netcdf.py
+++ b/earthkit/data/readers/netcdf.py
@@ -518,7 +518,7 @@ class XArrayMultiFieldList(XArrayFieldListCore, MultiIndex):
     def to_xarray(self, **kwargs):
         import xarray as xr
 
-        return xr.merge([x.ds for x in self.indexes], **kwargs)
+        return xr.merge([x.ds for x in self._indexes], **kwargs)
 
 
 class NetCDFMetadata(XArrayMetadata):
@@ -635,7 +635,7 @@ class NetCDFMultiFieldList(NetCDFFieldList, MultiIndex):
     def to_xarray(self, **kwargs):
         try:
             return NetCDFFieldList.to_xarray_multi_from_paths(
-                [x.path for x in self.indexes], **kwargs
+                [x.path for x in self._indexes], **kwargs
             )
         except AttributeError:
             # TODO: Implement this, but discussion required


Test patch:
diff --git a/tests/grib/test_grib_inidces.py b/tests/grib/test_grib_inidces.py
new file mode 100644
index 0000000..9d4f52b
--- /dev/null
+++ b/tests/grib/test_grib_inidces.py
@@ -0,0 +1,195 @@
+#!/usr/bin/env python3
+
+# (C) Copyright 2020 ECMWF.
+#
+# This software is licensed under the terms of the Apache Licence Version 2.0
+# which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
+# In applying this licence, ECMWF does not waive the privileges and immunities
+# granted to it by virtue of its status as an intergovernmental organisation
+# nor does it submit to any jurisdiction.
+#
+
+import os
+import sys
+
+import pytest
+
+here = os.path.dirname(__file__)
+sys.path.insert(0, here)
+from grib_fixtures import load_file_or_numpy_fs  # noqa: E402
+
+
+@pytest.mark.parametrize("mode", ["file", "numpy_fs"])
+def test_grib_indices_base(mode):
+    ds = load_file_or_numpy_fs("tuv_pl.grib", mode)
+
+    ref = {
+        "class": ["od"],
+        "stream": ["oper"],
+        "levtype": ["pl"],
+        "type": ["an"],
+        "expver": ["0001"],
+        "date": [20180801],
+        "time": [1200],
+        "domain": ["g"],
+        "number": [0],
+        "levelist": [300, 400, 500, 700, 850, 1000],
+        "param": ["t", "u", "v"],
+    }
+
+    r = ds.indices()
+    assert r == ref
+
+    ref = {
+        "levelist": [300, 400, 500, 700, 850, 1000],
+        "param": ["t", "u", "v"],
+    }
+    r = ds.indices(squeeze=True)
+    assert r == ref
+
+    ref = ["t", "u", "v"]
+    r = ds.index("param")
+    assert r == ref
+
+
+@pytest.mark.parametrize("mode", ["file", "numpy_fs"])
+def test_grib_indices_sel(mode):
+    ds = load_file_or_numpy_fs("tuv_pl.grib", mode)
+
+    ref = {
+        "class": ["od"],
+        "stream": ["oper"],
+        "levtype": ["pl"],
+        "type": ["an"],
+        "expver": ["0001"],
+        "date": [20180801],
+        "time": [1200],
+        "domain": ["g"],
+        "number": [0],
+        "levelist": [300, 400, 500, 700, 850, 1000],
+        "param": ["t"],
+    }
+
+    ds1 = ds.sel(param="t")
+    r = ds1.indices()
+    assert r == ref
+
+    ref = {
+        "levelist": [300, 400, 500, 700, 850, 1000],
+    }
+    r = ds1.indices(squeeze=True)
+    assert r == ref
+
+
+@pytest.mark.parametrize("mode", ["file", "numpy_fs"])
+def test_grib_indices_multi(mode):
+    f1 = load_file_or_numpy_fs("tuv_pl.grib", mode)
+    f2 = load_file_or_numpy_fs("ml_data.grib", mode, folder="data")
+    ds = f1 + f2
+
+    ref = {
+        "class": ["od"],
+        "stream": ["oper"],
+        "levtype": ["ml", "pl"],
+        "type": ["an", "fc"],
+        "expver": ["0001"],
+        "date": [20180111, 20180801],
+        "time": [1200],
+        "domain": ["g"],
+        "number": [0],
+        "levelist": [
+            1,
+            5,
+            9,
+            13,
+            17,
+            21,
+            25,
+            29,
+            33,
+            37,
+            41,
+            45,
+            49,
+            53,
+            57,
+            61,
+            65,
+            69,
+            73,
+            77,
+            81,
+            85,
+            89,
+            93,
+            97,
+            101,
+            105,
+            109,
+            113,
+            117,
+            121,
+            125,
+            129,
+            133,
+            137,
+            300,
+            400,
+            500,
+            700,
+            850,
+            1000,
+        ],
+        "param": ["lnsp", "t", "u", "v"],
+    }
+
+    r = ds.indices()
+    assert r == ref
+
+
+@pytest.mark.parametrize("mode", ["file", "numpy_fs"])
+def test_grib_indices_multi_Del(mode):
+    f1 = load_file_or_numpy_fs("tuv_pl.grib", mode)
+    f2 = load_file_or_numpy_fs("ml_data.grib", mode, folder="data")
+    ds = f1 + f2
+
+    ref = {
+        "class": ["od"],
+        "stream": ["oper"],
+        "levtype": ["ml", "pl"],
+        "type": ["an", "fc"],
+        "expver": ["0001"],
+        "date": [20180111, 20180801],
+        "time": [1200],
+        "domain": ["g"],
+        "number": [0],
+        "levelist": [93, 500],
+        "param": ["t"],
+    }
+
+    ds1 = ds.sel(param="t", level=[93, 500])
+    r = ds1.indices()
+    assert r == ref
+
+
+@pytest.mark.parametrize("mode", ["file", "numpy_fs"])
+def test_grib_indices_order_by(mode):
+    ds = load_file_or_numpy_fs("tuv_pl.grib", mode)
+
+    ref = {
+        "class": ["od"],
+        "stream": ["oper"],
+        "levtype": ["pl"],
+        "type": ["an"],
+        "expver": ["0001"],
+        "date": [20180801],
+        "time": [1200],
+        "domain": ["g"],
+        "number": [0],
+        "levelist": [300, 400, 500, 700, 850, 1000],
+        "param": ["t", "u", "v"],
+    }
+
+    ds1 = ds.order_by(levelist="descending")
+    r = ds1.indices()
+    assert r == ref
diff --git a/tests/indexing/test_indexing_db.py b/tests/indexing/test_indexing_db.py
index 84b3b93..77f3087 100644
--- a/tests/indexing/test_indexing_db.py
+++ b/tests/indexing/test_indexing_db.py
@@ -35,8 +35,8 @@ def test_indexing_db_file_multi():
     ds = from_source("file", path, indexing=True)
 
     counts = [6, 6, 6]
-    assert len(counts) == len(ds.indexes)
-    for i, d in enumerate(ds.indexes):
+    assert len(counts) == len(ds._indexes)
+    for i, d in enumerate(ds._indexes):
         assert hasattr(d, "db"), f"db,{i}"
         assert d.db.count() == counts[i]
 
diff --git a/tests/sources/test_cds.py b/tests/sources/test_cds.py
index a2a359c..bbdd08a 100644
--- a/tests/sources/test_cds.py
+++ b/tests/sources/test_cds.py
@@ -86,7 +86,7 @@ def test_cds_grib_split_on_var():
     assert len(s) == 2
     assert s.metadata("param") == ["2t", "msl"]
     assert not hasattr(s, "path")
-    assert len(s.indexes) == 2
+    assert len(s._indexes) == 2
 
 
 @pytest.mark.parametrize(
@@ -152,10 +152,10 @@ def test_cds_split_on(split_on, expected_file_num, expected_param, expected_time
 
     if expected_file_num == 1:
         assert hasattr(s, "path")
-        assert not hasattr(s, "indexes")
+        assert not hasattr(s, "_indexes")
     else:
         assert not hasattr(s, "path")
-        assert len(s.indexes) == expected_file_num
+        assert len(s._indexes) == expected_file_num
 
     assert len(s) == 4
     assert s.metadata("param") == expected_param
@@ -188,7 +188,7 @@ def test_cds_multiple_requests(
         base_request | {"variable": "2t", "split_on": split_on1},
         base_request | {"variable": "msl", "split_on": split_on2},
     )
-    assert len(s.indexes) == expected_file_num
+    assert len(s._indexes) == expected_file_num
     assert len(s) == 4
     assert s.metadata("param") == expected_param
     assert s.metadata("time") == expected_time