DOC: document support for in-memory HDFStore GH33166 (#34888)

Author: dennisbakhuis

doc/source/user_guide/cookbook.rst

@@ -1166,6 +1166,25 @@ Storing Attributes to a group node
    store.close()
    os.remove('test.h5')
 
+You can create or load a HDFStore in-memory  by passing the ``driver``
+parameter to PyTables. Changes are only written to disk when the HDFStore
+is closed.
+
+.. ipython:: python
+
+   store = pd.HDFStore('test.h5', 'w', diver='H5FD_CORE')
+
+   df = pd.DataFrame(np.random.randn(8, 3))
+   store['test'] = df
+
+   # only after closing the store, data is written to disk:
+   store.close()
+
+.. ipython:: python
+   :suppress:
+
+   os.remove('test.h5')
+
 .. _cookbook.binary:
 
 Binary files

pandas/io/pytables.py

@@ -447,8 +447,8 @@ class HDFStore:
 
     Parameters
     ----------
-    path : string
-        File path to HDF5 file
+    path : str
+        File path to HDF5 file.
     mode : {'a', 'w', 'r', 'r+'}, default 'a'
 
         ``'r'``
@@ -462,18 +462,20 @@ class HDFStore:
         ``'r+'``
             It is similar to ``'a'``, but the file must already exist.
     complevel : int, 0-9, default None
-            Specifies a compression level for data.
-            A value of 0 or None disables compression.
+        Specifies a compression level for data.
+        A value of 0 or None disables compression.
     complib : {'zlib', 'lzo', 'bzip2', 'blosc'}, default 'zlib'
-            Specifies the compression library to be used.
-            As of v0.20.2 these additional compressors for Blosc are supported
-            (default if no compressor specified: 'blosc:blosclz'):
-            {'blosc:blosclz', 'blosc:lz4', 'blosc:lz4hc', 'blosc:snappy',
-             'blosc:zlib', 'blosc:zstd'}.
-            Specifying a compression library which is not available issues
-            a ValueError.
+        Specifies the compression library to be used.
+        As of v0.20.2 these additional compressors for Blosc are supported
+        (default if no compressor specified: 'blosc:blosclz'):
+        {'blosc:blosclz', 'blosc:lz4', 'blosc:lz4hc', 'blosc:snappy',
+         'blosc:zlib', 'blosc:zstd'}.
+        Specifying a compression library which is not available issues
+        a ValueError.
     fletcher32 : bool, default False
-            If applying compression use the fletcher32 checksum
+        If applying compression use the fletcher32 checksum.
+    **kwargs
+        These parameters will be passed to the PyTables open_file method.
 
     Examples
     --------
@@ -482,6 +484,17 @@ class HDFStore:
     >>> store['foo'] = bar   # write to HDF5
     >>> bar = store['foo']   # retrieve
     >>> store.close()
+
+    **Create or load HDF5 file in-memory**
+
+    When passing the `driver` option to the PyTables open_file method through
+    **kwargs, the HDF5 file is loaded or created in-memory and will only be
+    written when closed:
+
+    >>> bar = pd.DataFrame(np.random.randn(10, 4))
+    >>> store = pd.HDFStore('test.h5', driver='H5FD_CORE')
+    >>> store['foo'] = bar
+    >>> store.close()   # only now, data is written to disk
     """
 
     _handle: Optional["File"]
@@ -634,6 +647,8 @@ def open(self, mode: str = "a", **kwargs):
         ----------
         mode : {'a', 'w', 'r', 'r+'}, default 'a'
             See HDFStore docstring or tables.open_file for info about modes
+        **kwargs
+            These parameters will be passed to the PyTables open_file method.
         """
         tables = _tables()