BF: Fix interaction between indexed_gzip presence and keep_file_open flag

nibabel/arrayproxy.py

@@ -42,11 +42,14 @@
 used for the lifetime of the ``ArrayProxy``. It should be set to one of
 ``True``, ``False``, or ``'auto'``.
 
-If ``True``, a single file handle is created and used. If ``False``, a new
-file handle is created every time the image is accessed. For gzip files, if
-``'auto'``, and the optional ``indexed_gzip`` dependency is present, a single
-file handle is created and persisted. If ``indexed_gzip`` is not available,
-behaviour is the same as if ``keep_file_open is False``.
+Management of file handles will be performed either by ``ArrayProxy`` objects,
+or by the ``indexed_gzip`` package if it is used.
+
+If this flag is set to ``True``, a single file handle is created and used. If
+``False``, a new file handle is created every time the image is accessed. For
+gzip files, if ``'auto'``, and the optional ``indexed_gzip`` dependency is
+present, a single file handle is created and persisted. If ``indexed_gzip`` is
+not available, behaviour is the same as if ``keep_file_open is False``.
 
 If this is set to any other value, attempts to create an ``ArrayProxy`` without
 specifying the ``keep_file_open`` flag will result in a ``ValueError`` being
@@ -160,8 +163,10 @@ def __init__(self, file_like, spec, mmap=True, keep_file_open=None):
         # Permit any specifier that can be interpreted as a numpy dtype
         self._dtype = np.dtype(self._dtype)
         self._mmap = mmap
-        self._keep_file_open = self._should_keep_file_open(file_like,
-                                                           keep_file_open)
+        # Flags to keep track of whether a single ImageOpener is created, and
+        # whether a single underlying file handle is created.
+        self._keep_file_open, self._persist_opener = \
+            self._should_keep_file_open(file_like, keep_file_open)
         self._lock = RLock()
 
     def __del__(self):
@@ -184,16 +189,64 @@ def __setstate__(self, state):
         self._lock = RLock()
 
     def _should_keep_file_open(self, file_like, keep_file_open):
-        """Called by ``__init__``, and used to determine the final value of
-        ``keep_file_open``.
+        """Called by ``__init__``.
+
+        This method determines how to manage ``ImageOpener`` instances,
+        and the underlying file handles - the behaviour depends on:
+
+         - whether ``file_like`` is an an open file handle, or a path to a
+           ``'.gz'`` file, or a path to a non-gzip file.
+         - whether ``indexed_gzip`` is present (see
+           :attr:`.openers.HAVE_INDEXED_GZIP`).
+
+        An ``ArrayProxy`` object uses two internal flags to manage
+        ``ImageOpener`` instances and underlying file handles.
+
+          - The ``_persist_opener`` flag controls whether a single
+            ``ImageOpener`` should be created and used for the lifetime of
+            this ``ArrayProxy``, or whether separate ``ImageOpener`` instances
+            should be created on each file access.
+
+          - The ``_keep_file_open`` flag controls qwhether the underlying file
+            handle should be kept open for the lifetime of this
+            ``ArrayProxy``, or whether the file handle should be (re-)opened
+            and closed on each file access.
+
+        The internal ``_keep_file_open`` flag is only relevant if
+        ``file_like`` is a ``'.gz'`` file, and the ``indexed_gzip`` library is
+        present.
 
-        The return value is derived from these rules:
+        This method returns the values to be used for the internal
+        ``_persist_opener`` and ``_keep_file_open`` flags; these values are
+        derived according to the following rules:
 
-          - If ``file_like`` is a file(-like) object, ``False`` is returned.
-            Otherwise, ``file_like`` is assumed to be a file name.
-          - If ``keep_file_open`` is ``auto``, and ``indexed_gzip`` is
-            not available, ``False`` is returned.
-          - Otherwise, the value of ``keep_file_open`` is returned unchanged.
+        1. If ``file_like`` is a file(-like) object, both flags are set to
+        ``False``.
+
+        2. If ``keep_file_open`` (as passed to :meth:``__init__``) is
+           ``True``, both internal flags are set to ``True``.
+
+        3. If ``keep_file_open`` is ``False``, but ``file_like`` is not a path
+           to a ``.gz`` file or ``indexed_gzip`` is not present, both flags
+           are set to ``False``.
+
+        4. If ``keep_file_open`` is ``False``, ``file_like`` is a path to a
+           ``.gz`` file, and ``indexed_gzip`` is present, ``_persist_opener``
+           is set to ``True``, and ``_keep_file_open`` is set to ``False``.
+           In this case, file handle management is delegated to the
+           ``indexed_gzip`` library.
+
+        5. If ``keep_file_open`` is ``'auto'``, ``file_like`` is a path to a
+           ``.gz`` file, and ``indexed_gzip`` is present, both internal flags
+           are set to ``True``.
+
+        6. If ``keep_file_open`` is ``'auto'``, and ``file_like`` is not a
+           path to a ``.gz`` file, or ``indexed_gzip`` is not present, both
+           internal flags are set to ``False``.
+
+        Note that a value of ``'auto'`` for ``keep_file_open`` will become
+        deprecated behaviour in version 2.4.0, and support for ``'auto'`` will
+        be removed in version 3.0.0.
 
         Parameters
         ----------
@@ -206,8 +259,10 @@ def _should_keep_file_open(self, file_like, keep_file_open):
         Returns
         -------
 
-        The value of ``keep_file_open`` that will be used by this
-        ``ArrayProxy``, and passed through to ``ImageOpener`` instances.
+        A tuple containing:
+          - ``keep_file_open`` flag to control persistence of file handles
+          - ``persist_opener`` flag to control persistence of ``ImageOpener``
+            objects.
         """
         if keep_file_open is None:
             keep_file_open = KEEP_FILE_OPEN_DEFAULT
@@ -216,12 +271,15 @@ def _should_keep_file_open(self, file_like, keep_file_open):
                              '\'auto\', True, False}')
         # file_like is a handle - keep_file_open is irrelevant
         if hasattr(file_like, 'read') and hasattr(file_like, 'seek'):
-            return False
-        # don't have indexed_gzip - auto -> False
-        if keep_file_open == 'auto' and not (openers.HAVE_INDEXED_GZIP and
-                                             file_like.endswith('.gz')):
-            return False
-        return keep_file_open
+            return False, False
+        # if the file is a gzip file, and we have_indexed_gzip,
+        have_igzip = openers.HAVE_INDEXED_GZIP and file_like.endswith('.gz')
+        if keep_file_open == 'auto':
+            return have_igzip, have_igzip
+        elif keep_file_open:
+            return True, True
+        else:
+            return False, have_igzip
 
     @property
     @deprecate_with_version('ArrayProxy.header deprecated', '2.2', '3.0')
@@ -265,13 +323,14 @@ def _get_fileobj(self):
             A newly created ``ImageOpener`` instance, or an existing one,
             which provides access to the file.
         """
-        if self._keep_file_open:
+        if self._persist_opener:
             if not hasattr(self, '_opener'):
                 self._opener = openers.ImageOpener(
                     self.file_like, keep_open=self._keep_file_open)
             yield self._opener
         else:
-            with openers.ImageOpener(self.file_like) as opener:
+            with openers.ImageOpener(
+                    self.file_like, keep_open=False) as opener:
                 yield opener
 
     def get_unscaled(self):