Add attrname parameter

src/fscacher/cache.py

@@ -1,5 +1,5 @@
 from collections import deque, namedtuple
-from functools import wraps
+from functools import partial, wraps
 from inspect import Parameter, signature
 import logging
 import os
@@ -73,7 +73,10 @@ def memoize(self, f):
             return f
         return self._memory.cache(f)
 
-    def memoize_path(self, f):
+    def memoize_path(self, f=None, *, attrname=None):
+        if f is None:
+            return partial(self.memoize_path, attrname=attrname)
+
         # we need to actually decorate a function
         fingerprint_kwarg = "_cache_fingerprint"
 
@@ -99,6 +102,8 @@ def fingerprinted(path, *args, **kwargs):
         def fingerprinter(path, *args, **kwargs):
             # we need to dereference symlinks and use that path in the function
             # call signature
+            if attrname is not None:
+                path = getattr(path, attrname)
             path_orig = path
             path = op.realpath(path)
             if path != path_orig:

src/fscacher/tests/test_cache.py

@@ -388,3 +388,94 @@ def git(*args):
     assert len(calls) == 1
     assert memoread(tmp_path / "subdir" / "text.txt") == content
     assert len(calls) == 1
+
+
+def test_memoize_path_attrname(cache, tmp_path):
+    calls = []
+
+    class Foo:
+        def __init__(self, name, path):
+            self.name = name
+            self.path = path
+            self.extra = 0
+
+        @cache.memoize_path(attrname="path")
+        def memoread(self, arg, kwarg=None):
+            calls.append([self.path, arg, kwarg])
+            with open(self.path) as f:
+                return f.read()
+
+    def check_new_memoread(obj, arg, content, expect_new=False):
+        ncalls = len(calls)
+        assert obj.memoread(arg) == content
+        assert len(calls) == ncalls + 1
+        assert obj.memoread(arg) == content
+        assert len(calls) == ncalls + 1 + int(expect_new)
+
+    path = str(tmp_path / "file.dat")
+    foo = Foo("foo", path)
+
+    with pytest.raises(IOError):
+        foo.memoread(0)
+    # and again
+    with pytest.raises(IOError):
+        foo.memoread(0)
+    assert len(calls) == 2
+
+    with open(path, "w") as f:
+        f.write("content")
+
+    t0 = time.time()
+    try:
+        # unless this computer is too slow -- there should be less than
+        # cache._min_dtime between our creating the file and testing,
+        # so we would force a direct read:
+        check_new_memoread(foo, 0, "content", True)
+    except AssertionError:  # pragma: no cover
+        # if computer is indeed slow (happens on shared CIs) we might fail
+        # because distance is too short
+        if time.time() - t0 < cache._min_dtime:
+            raise  # if we were quick but still failed -- legit
+    assert calls[-1] == [path, 0, None]
+
+    # but if we sleep - should memoize
+    time.sleep(cache._min_dtime * 1.1)
+    check_new_memoread(foo, 1, "content")
+
+    # and if we modify the file -- a new read
+    time.sleep(cache._min_dtime * 1.1)
+    with open(path, "w") as f:
+        f.write("Content")
+    ncalls = len(calls)
+    assert foo.memoread(1) == "Content"
+    assert len(calls) == ncalls + 1
+
+    # If we modify the instance, a new read
+    foo.extra = 1
+    ncalls = len(calls)
+    assert foo.memoread(1) == "Content"
+    assert len(calls) == ncalls + 1
+
+    # Another, unequal instance gets its own read
+    bar = Foo("bar", path)
+    ncalls = len(calls)
+    assert bar.memoread(1) == "Content"
+    assert len(calls) == ncalls + 1
+    assert bar.memoread(1) == "Content"
+    assert len(calls) == ncalls + 1
+
+    # Another instance pointing to a different path gets its own read
+    path2 = str(tmp_path / "path2.txt")
+    with open(path2, "w") as fp:
+        print("Different content", file=fp)
+    baz = Foo("foo", path2)
+    ncalls = len(calls)
+    assert baz.memoread(1) == "Different content\n"
+    assert len(calls) == ncalls + 1
+    assert baz.memoread(1) == "Different content\n"
+    assert len(calls) == ncalls + 1
+
+    assert foo.memoread(1) == "Content"
+    assert len(calls) == ncalls + 1
+    assert bar.memoread(1) == "Content"
+    assert len(calls) == ncalls + 1