address review feedback

tldextract/cache.py

@@ -49,25 +49,27 @@ def get_cache_dir():
     Get a cache dir that we have permission to write to
 
     Try to follow the XDG standard, but if that doesn't work fallback to the package directory
+    http://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html
     """
-    try:
-        # http://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html
-        xdg_cache_home = os.getenv("XDG_CACHE_HOME", None)
-        if xdg_cache_home is None:
-            user_home = os.getenv("HOME", None)
+    cache_dir = os.environ.get("TLDEXTRACT_CACHE", None)
+    if cache_dir is not None:
+        return cache_dir
+
+    xdg_cache_home = os.getenv("XDG_CACHE_HOME", None)
+    if xdg_cache_home is None:
+        user_home = os.getenv("HOME", None)
+        if user_home:
             xdg_cache_home = os.path.join(user_home, ".cache")
-        pkg_id = get_pkg_unique_identifier()
-        cache_dir_default = os.path.join(xdg_cache_home, "python-tldextract", pkg_id)
 
-        return os.path.expanduser(os.environ.get("TLDEXTRACT_CACHE", cache_dir_default))
-    except TypeError:  # noqa
-        # fallback to trying to use package directory itself
-        return os.path.join(os.path.dirname(__file__), ".suffix_cache/")
+    if xdg_cache_home is not None:
+        return os.path.join(xdg_cache_home, "python-tldextract", get_pkg_unique_identifier())
+
+    # fallback to trying to use package directory itself
+    return os.path.join(os.path.dirname(__file__), ".suffix_cache/")
 
 
 class DiskCache:
     """Disk _cache that only works for jsonable values"""
-    NOT_SET = object()
 
     def __init__(self, cache_dir, lock_timeout=20):
         self.enabled = bool(cache_dir)