diff --git a/docs/reading_files.rst b/docs/reading_files.rst
index 31b9f639..bf549cef 100644
--- a/docs/reading_files.rst
+++ b/docs/reading_files.rst
@@ -268,6 +268,16 @@ methods offer extra capabilities.
 Getting data by train
 ---------------------
 
+Selecting trains in a run, source or key data returns a new object with a subset
+of the data matching the train selection. For example, You can do::
+
+    # run data
+    run = run[:100]  # first 100 trains in the run
+    # source data
+    source = source[by_id[12345678]]  # data for train ID == 1234568
+    # key data
+    key = key[np.s_[10:20]]  # data for the 10th to the 20th trains
+
 Some kinds of data, e.g. from AGIPD, are too big to load a whole run into
 memory at once. In these cases, it's convenient to load one train at a time.
 
diff --git a/extra_data/reader.py b/extra_data/reader.py
index f38fc230..e18b128d 100644
--- a/extra_data/reader.py
+++ b/extra_data/reader.py
@@ -33,17 +33,17 @@
 import numpy as np
 
 from . import locality, voview
+from .aliases import AliasIndexer
 from .exceptions import (MultiRunError, PropertyNameError, SourceNameError,
                          TrainIDError)
 from .file_access import FileAccess
 from .keydata import KeyData
-from .read_machinery import (DETECTOR_SOURCE_RE, FilenameInfo, by_id, by_index,
-                             find_proposal, glob_wildcards_re, same_run,
-                             select_train_ids, split_trains)
+from .read_machinery import (DETECTOR_SOURCE_RE, by_id, by_index,
+                             find_proposal, glob_wildcards_re, is_int_like,
+                             same_run, select_train_ids)
 from .run_files_map import RunFilesMap
 from .sourcedata import SourceData
 from .utils import available_cpu_cores
-from .aliases import AliasIndexer
 
 __all__ = [
     'H5File',
@@ -274,12 +274,21 @@ def _get_source_data(self, source):
         return self._sources_data[source]
 
     def __getitem__(self, item):
-        if isinstance(item, tuple) and len(item) == 2:
+        if (
+            isinstance(item, tuple) and
+            len(item) == 2 and
+            all(isinstance(e, str) for e in item)
+        ):
             return self._get_key_data(*item)
         elif isinstance(item, str):
             return self._get_source_data(item)
+        elif (
+            isinstance(item, (by_id, by_index, list, np.ndarray, slice)) or
+            is_int_like(item)
+        ):
+            return self.select_trains(item)
 
-        raise TypeError("Expected data[source] or data[source, key]")
+        raise TypeError("Expected data[source], data[source, key] or data[train_selection]")
 
     def _ipython_key_completions_(self):
         return list(self.all_sources)
diff --git a/extra_data/sourcedata.py b/extra_data/sourcedata.py
index 5897cdc0..215a2142 100644
--- a/extra_data/sourcedata.py
+++ b/extra_data/sourcedata.py
@@ -2,15 +2,15 @@
 import re
 from typing import Dict, List, Optional
 
-import numpy as np
 import h5py
+import numpy as np
 
-from .exceptions import MultiRunError, PropertyNameError, NoDataError
+from .exceptions import MultiRunError, NoDataError, PropertyNameError
 from .file_access import FileAccess
 from .keydata import KeyData
-from .read_machinery import (
-    glob_wildcards_re, same_run, select_train_ids, split_trains, trains_files_index
-)
+from .read_machinery import (by_id, by_index, glob_wildcards_re, is_int_like,
+                             same_run, select_train_ids, split_trains,
+                             trains_files_index)
 
 
 class SourceData:
@@ -67,6 +67,12 @@ def __contains__(self, key):
         return res
 
     def __getitem__(self, key):
+        if (
+            isinstance(key, (by_id, by_index, list, np.ndarray, slice)) or
+            is_int_like(key)
+        ):
+            return self.select_trains(key)
+
         if key not in self:
             raise PropertyNameError(key, self.source)
         ds0 = self.files[0].file[
diff --git a/extra_data/tests/test_reader_mockdata.py b/extra_data/tests/test_reader_mockdata.py
index b608a6ed..fa536d51 100644
--- a/extra_data/tests/test_reader_mockdata.py
+++ b/extra_data/tests/test_reader_mockdata.py
@@ -607,6 +607,10 @@ def test_select(mock_fxe_raw_run):
     assert sel_by_kd.control_sources == {kd.source}
     assert sel_by_kd.keys_for_source(kd.source) == {kd.key}
 
+    # disallow mixing source and train ID selection
+    with pytest.raises(TypeError):
+        run['SPB_XTD9_XGM/DOOCS/MAIN', 10]
+
 
 @pytest.mark.parametrize(
     'select_str',
@@ -717,6 +721,12 @@ def test_select_trains(mock_fxe_raw_run):
     with pytest.raises(IndexError):
         run.select_trains(by_index[[480]])
 
+    assert run[10].train_ids == [10010]
+    assert run[by_id[10000]].train_ids == [10000]
+    assert run[by_index[479:555]].train_ids == [10479]
+    with pytest.raises(IndexError):
+        run[555]
+
 
 def test_split_trains(mock_fxe_raw_run):
     run = RunDirectory(mock_fxe_raw_run)
diff --git a/extra_data/tests/test_sourcedata.py b/extra_data/tests/test_sourcedata.py
index e1183c6e..a237eedc 100644
--- a/extra_data/tests/test_sourcedata.py
+++ b/extra_data/tests/test_sourcedata.py
@@ -114,6 +114,19 @@ def test_select_trains(mock_spb_raw_run):
     assert sel.train_ids == []
     assert sel.keys() == xgm.keys()
 
+    sel = xgm[by_id[10020:10040]]
+    assert sel.train_ids == list(range(10020, 10040))
+
+    sel = xgm[by_index[:10]]
+    assert sel.train_ids == list(range(10000, 10010))
+
+    sel = xgm[10]
+    assert sel.train_ids == [10010]
+
+    sel = xgm[999:1000]
+    assert sel.train_ids == []
+    assert sel.keys() == xgm.keys()
+
 
 def test_split_trains(mock_spb_raw_run):
     run = RunDirectory(mock_spb_raw_run)