new function is_module_pickle()

dill/__init__.py

@@ -25,10 +25,10 @@
 
 from ._dill import (
     dump, dumps, load, loads, dump_module, load_module, load_module_asdict,
-    dump_session, load_session, Pickler, Unpickler, register, copy, pickle,
-    pickles, check, HIGHEST_PROTOCOL, DEFAULT_PROTOCOL, PicklingError,
-    UnpicklingError, HANDLE_FMODE, CONTENTS_FMODE, FILE_FMODE, PickleError,
-    PickleWarning, PicklingWarning, UnpicklingWarning,
+    dump_session, load_session, is_module_pickle, Pickler, Unpickler, register,
+    copy, pickle, pickles, check, HIGHEST_PROTOCOL, DEFAULT_PROTOCOL,
+    PicklingError, UnpicklingError, HANDLE_FMODE, CONTENTS_FMODE, FILE_FMODE,
+    PickleError, PickleWarning, PicklingWarning, UnpicklingWarning,
 )
 from . import source, temp, detect
 

dill/_dill.py

@@ -17,11 +17,11 @@
 """
 __all__ = [
     'dump', 'dumps', 'load', 'loads', 'dump_module', 'load_module',
-    'load_module_asdict', 'dump_session', 'load_session', 'Pickler', 'Unpickler',
-    'register', 'copy', 'pickle', 'pickles', 'check', 'HIGHEST_PROTOCOL',
-    'DEFAULT_PROTOCOL', 'PicklingError', 'UnpicklingError', 'HANDLE_FMODE',
-    'CONTENTS_FMODE', 'FILE_FMODE', 'PickleError', 'PickleWarning',
-    'PicklingWarning', 'UnpicklingWarning'
+    'load_module_asdict', 'dump_session', 'load_session', 'is_module_pickle',
+    'Pickler', 'Unpickler', 'register', 'copy', 'pickle', 'pickles', 'check',
+    'HIGHEST_PROTOCOL', 'DEFAULT_PROTOCOL', 'PicklingError', 'UnpicklingError',
+    'HANDLE_FMODE', 'CONTENTS_FMODE', 'FILE_FMODE', 'PickleError',
+    'PickleWarning', 'PicklingWarning', 'UnpicklingWarning',
 ]
 
 __module__ = 'dill'
@@ -606,6 +606,28 @@ def _identify_module(file, main=None):
             return None
         raise UnpicklingError("unable to identify main module") from error
 
+def is_module_pickle(filename, importable: bool = True) -> bool:
+    """Check if a file is a module state pickle file.
+
+    Parameters:
+        filename: a path-like object or a readable stream.
+        importable: expected kind of the file's saved module. Use `True` for
+            importable modules (the default) or `False` for module-type objects.
+
+    Returns:
+        `True` if the pickle file at ``filename`` was generated with
+        :py:func:`dump_module` **AND** the module whose state is saved in it is
+        of the kind specified by the ``importable`` argument. `False` otherwise.
+    """
+    with _open(filename, 'rb', peekable=True) as file:
+        try:
+            pickle_main = _identify_module(file)
+        except UnpicklingError:
+            return False
+        else:
+            is_runtime_mod = pickle_main.startswith('__runtime__.')
+            return importable ^ is_runtime_mod
+
 def load_module(
     filename = str(TEMPDIR/'session.pkl'),
     module: Union[ModuleType, str] = None,