diff --git a/README.rst b/README.rst
index a05b883..03df49f 100644
--- a/README.rst
+++ b/README.rst
@@ -54,6 +54,8 @@ To do this, filefinder2 includes finder and loader hooks that contain the implic
 
 It is worth noting that we achieve this without pkg_resources or pkgutil, minimizing the dependencies necessary for that feature.
 
+Credits to importlib2 (and CPython) for providing the foundations for this.
+
 Usage:
 ------
 ::
diff --git a/filefinder2/_cache_utils.py b/filefinder2/_cache_utils.py
new file mode 100644
index 0000000..61270db
--- /dev/null
+++ b/filefinder2/_cache_utils.py
@@ -0,0 +1,67 @@
+import os
+import sys
+
+_PYCACHE = '__pycache__'
+
+SOURCE_SUFFIXES = [b'.py']  # _setup() adds .pyw as needed.
+
+DEBUG_BYTECODE_SUFFIXES = [b'.pyc']
+OPTIMIZED_BYTECODE_SUFFIXES = [b'.pyo']
+
+# Alternatives : (from hylang)
+#     elif hasattr(imp, "cache_from_source"):
+#         return imp.cache_from_source(source_path)
+#     else:
+#         # If source_path has a file extension, replace it with ".pyc".
+#         # Otherwise, just append ".pyc".
+#         d, f = os.path.split(source_path)
+#         return os.path.join(d, re.sub(r"(?:\.[^.]+)?\Z", ".pyc", f))
+
+def cache_from_source(path, debug_override=None):
+    """Given the path to a .py file, return the path to its .pyc/.pyo file.
+
+    The .py file does not need to exist; this simply returns the path to the
+    .pyc/.pyo file calculated as if the .py file were imported.  The extension
+    will be .pyc unless sys.flags.optimize is non-zero, then it will be .pyo.
+
+    If debug_override is not None, then it must be a boolean and is used in
+    place of sys.flags.optimize.
+
+    If sys.implementation.cache_tag is None then NotImplementedError is raised.
+
+    """
+    debug = not sys.flags.optimize if debug_override is None else debug_override
+    if debug:
+        suffixes = DEBUG_BYTECODE_SUFFIXES
+    else:
+        suffixes = OPTIMIZED_BYTECODE_SUFFIXES
+    head, tail = os.path.split(path)
+    base_filename, sep, _ = tail.partition('.')
+    tag = sys.implementation.cache_tag
+    if tag is None:
+        raise NotImplementedError('sys.implementation.cache_tag is None')
+    filename = ''.join([base_filename, sep, tag, suffixes[0]])
+    return os.path.join(head, _PYCACHE, filename)
+
+
+def source_from_cache(path):
+    """Given the path to a .pyc./.pyo file, return the path to its .py file.
+
+    The .pyc/.pyo file does not need to exist; this simply returns the path to
+    the .py file calculated to correspond to the .pyc/.pyo file.  If path does
+    not conform to PEP 3147 format, ValueError will be raised. If
+    sys.implementation.cache_tag is None then NotImplementedError is raised.
+
+    """
+    if sys.implementation.cache_tag is None:
+        raise NotImplementedError('sys.implementation.cache_tag is None')
+    head, pycache_filename = os.path.split(path)
+    head, pycache = os.path.split(head)
+    if pycache != _PYCACHE:
+        raise ValueError('{} not bottom-level directory in '
+                         '{!r}'.format(_PYCACHE, path))
+    if pycache_filename.count('.') != 2:
+        raise ValueError('expected only 2 dots in '
+                         '{!r}'.format(pycache_filename))
+    base_filename = pycache_filename.partition('.')[0]
+    return os.path.join(head, base_filename + SOURCE_SUFFIXES[0])
diff --git a/filefinder2/util.py b/filefinder2/util.py
index 9c99d48..6ef9cbb 100644
--- a/filefinder2/util.py
+++ b/filefinder2/util.py
@@ -7,9 +7,8 @@
 from ._spec_utils import spec_from_loader
 from ._spec_utils import _find_spec
 # from ._ import MAGIC_NUMBER, _BACKCOMPAT_MAGIC_NUMBER
-# from ._ import cache_from_source
+from ._cache_utils import cache_from_source, source_from_cache
 from ._encoding_utils import decode_source
-# from ._ import source_from_cache
 from ._spec_utils import spec_from_file_location
 
 import sys