Add better error message if parent path exists but isn't a directory

3 files changed, 22 insertions, 7 deletions

diff --git a/HISTORY.md b/HISTORY.md
index 79839a9..f86478f 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -3,6 +3,7 @@
 ## 0.8.2 (Unreleased)
 * Use `Cache-Control` **request** headers by default
 * Support `expire_after` param for `CachedSession.send()`
+* Filesystem and SQLite backends: Add better error message if parent path exists but isn't a directory
 * Make per-request expiration thread-safe for both `CachedSession.request()` and `CachedSession.send()`
 * Handle some additional corner cases when normalizing request data
 * Some micro-optimizations for request matching
diff --git a/requests_cache/backends/sqlite.py b/requests_cache/backends/sqlite.py
index def6c13..aa7f4d4 100644
--- a/requests_cache/backends/sqlite.py
+++ b/requests_cache/backends/sqlite.py
@@ -145,14 +145,13 @@ class SQLiteDict(BaseStorage):
         **kwargs,
     ):
         super().__init__(**kwargs)
+        self._can_commit = True
+        self._local_context = threading.local()
+        self._lock = threading.RLock()
         self.connection_kwargs = get_valid_kwargs(sqlite_template, kwargs)
         self.db_path = _get_sqlite_cache_path(db_path, use_cache_dir, use_temp, use_memory)
         self.fast_save = fast_save
         self.table_name = table_name
-
-        self._lock = threading.RLock()
-        self._can_commit = True
-        self._local_context = threading.local()
         self.init_db()
 
     def init_db(self):
@@ -312,9 +311,15 @@ def get_cache_path(db_path: AnyPath, use_cache_dir: bool = False, use_temp: bool
     elif use_temp and not db_path.is_absolute():
         db_path = Path(gettempdir()) / db_path
 
-    # Expand relative and user paths (~/*), and make sure parent dirs exist
+    # Expand relative and user paths (~), make parent dir(s), and better error if parent is a file
     db_path = db_path.absolute().expanduser()
-    db_path.parent.mkdir(parents=True, exist_ok=True)
+    try:
+        db_path.parent.mkdir(parents=True, exist_ok=True)
+    except FileExistsError:
+        raise FileExistsError(
+            f'Parent path exists and is not a directory: {db_path.parent}.'
+            'Please either delete the file or choose a different path.'
+        )
     return db_path
 
 
diff --git a/tests/integration/test_sqlite.py b/tests/integration/test_sqlite.py
index 67ab7a8..1840a78 100644
--- a/tests/integration/test_sqlite.py
+++ b/tests/integration/test_sqlite.py
@@ -1,8 +1,10 @@
 import os
-from tempfile import gettempdir
+from os.path import join
+from tempfile import NamedTemporaryFile, gettempdir
 from threading import Thread
 from unittest.mock import patch
 
+import pytest
 from appdirs import user_cache_dir
 
 from requests_cache.backends.base import BaseCache
@@ -51,6 +53,13 @@ class SQLiteTestCase(BaseStorageTest):
     def test_use_memory__uri(self):
         self.init_cache(':memory:').db_path == ':memory:'
 
+    def test_non_dir_parent_exists(self):
+        """Expect a custom error message if a parent path already exists but isn't a directory"""
+        with NamedTemporaryFile() as tmp:
+            with pytest.raises(FileExistsError) as exc_info:
+                self.storage_class(join(tmp.name, 'invalid_path'))
+                assert 'not a directory' in str(exc_info.value)
+
     def test_bulk_commit(self):
         cache = self.init_cache()
         with cache.bulk_commit():