diff --git a/.github/workflows/run_python_tests.yml b/.github/workflows/run_python_tests.yml
index 5f985ee..e8239cc 100644
--- a/.github/workflows/run_python_tests.yml
+++ b/.github/workflows/run_python_tests.yml
@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.7", "3.8", "3.9", "3.10"]
+        python-version: ["3.7", "3.8", "3.9", "3.10", "3.11", "3.12"]
 
     steps:
     - uses: actions/checkout@v2
diff --git a/lazy_dataset/__init__.py b/lazy_dataset/__init__.py
index d7fecab..a0ca21b 100644
--- a/lazy_dataset/__init__.py
+++ b/lazy_dataset/__init__.py
@@ -1,3 +1,4 @@
+from . import core
 from .core import (
     new,
     concatenate,
@@ -7,6 +8,7 @@
     from_dict,
     from_list,
     from_dataset,
+    from_file,
     FilterException,
 )
-from.core import _zip as zip
+from .core import _zip as zip
diff --git a/lazy_dataset/core.py b/lazy_dataset/core.py
index b9ab2d2..549159a 100644
--- a/lazy_dataset/core.py
+++ b/lazy_dataset/core.py
@@ -201,6 +201,20 @@ def from_dataset(
         >>> ds = from_dataset(new({'a': 1, 'b': 2, 'c': 3, 'd': 4}).filter(lambda x: x%2))
         >>> dict(ds)
         {'a': 1, 'c': 3}
+
+        # Works with concatenated datasets and duplicated keys
+        >>> ds = new({'a': 1, 'b': 2})
+        >>> ds = concatenate(ds, ds)
+        >>> ds
+            DictDataset(len=2)
+          MapDataset(_pickle.loads)
+            DictDataset(len=2)
+          MapDataset(_pickle.loads)
+        ConcatenateDataset()
+        >>> from_dataset(ds)
+          ListDataset(len=4)
+        MapDataset(_pickle.loads)
+
     """
     try:
         items = list(examples.items())
@@ -208,8 +222,14 @@ def from_dataset(
         return from_list(list(examples),
                          immutable_warranty=immutable_warranty, name=name)
     else:
-        return from_dict(dict(items),
-                         immutable_warranty=immutable_warranty, name=name)
+        new = dict(items)
+        if len(new) == len(items):
+            return from_dict(new,
+                            immutable_warranty=immutable_warranty, name=name)
+        else:
+            # Duplicates in keys
+            return from_list(list(map(operator.itemgetter(1), items)),
+                             immutable_warranty=immutable_warranty, name=name)
 
 
 def concatenate(*datasets):
@@ -417,7 +437,10 @@ def copy(self, freeze: bool = False) -> 'Dataset':
         Returns:
             A copy of this dataset
         """
-        raise NotImplementedError
+        raise NotImplementedError(
+            f'copy is not implemented for {self.__class__}.\n'
+            f'self: \n{repr(self)}'
+        )
 
     def __iter__(self, with_key=False):
         if with_key:
@@ -2973,6 +2996,7 @@ def __init__(self, *input_datasets):
             ]
             raise AssertionError(
                 f'Expect that all input_datasets have the same keys. '
+                f'Missing: {lengths} of {len(keys)}\n'
                 f'Missing keys: '
                 f'{missing_keys}\n{self.input_datasets}'
             )
@@ -3067,8 +3091,8 @@ class ItemsDataset(Dataset):
     >>> ds_nokeys_rng = ds_plain.shuffle(True, rng=np.random.RandomState(0))  # No keys
     >>> list(ds_nokeys.map(lambda x: x + 10).items())
     [('a', 11), ('b', 12), ('c', 13)]
-    >>> list(ds_nokeys.concatenate(ds_plain).items())
-    [('a', 1), ('b', 2), ('c', 3), ('a', 1), ('b', 2), ('c', 3)]
+    >>> list(ds_nokeys.map(lambda x: x + 10).concatenate(ds_plain).filter(lambda x: x in [1, 12, 13]).items())
+    [('b', 12), ('c', 13), ('a', 1)]
     >>> list(ds_nokeys_rng.intersperse(ds_nokeys_rng).items())
     [('c', 3), ('a', 1), ('c', 3), ('c', 3), ('b', 2), ('b', 2)]
     >>> list(ds_plain.key_zip(ds_plain).items())