Raise error during instantiation when FileCache dependency lockfile is missing

This prevents the same error from being printed to stdout when importing
the RedisCache class and not using FileCache at all.

Author: jezdez

cachecontrol/caches/__init__.py

@@ -1,18 +1,2 @@
-from textwrap import dedent
-
-try:
-    from .file_cache import FileCache  # noqa
-except ImportError:
-    notice = dedent('''
-    NOTE: In order to use the FileCache you must have
-    lockfile installed. You can install it via pip:
-      pip install lockfile
-    ''')
-    print(notice)
-
-
-try:
-    import redis  # noqa
-    from .redis_cache import RedisCache  # noqa
-except ImportError:
-    pass
+from .file_cache import FileCache  # noqa
+from .redis_cache import RedisCache  # noqa

cachecontrol/caches/file_cache.py

@@ -1,8 +1,7 @@
 import hashlib
 import os
-
-from lockfile import LockFile
-from lockfile.mkdirlockfile import MkdirLockFile
+import warnings
+from textwrap import dedent
 
 from ..cache import BaseCache
 from ..controller import CacheController
@@ -55,19 +54,29 @@ def __init__(self, directory, forever=False, filemode=0o0600,
         if use_dir_lock is not None and lock_class is not None:
             raise ValueError("Cannot use use_dir_lock and lock_class together")
 
-        if use_dir_lock:
-            lock_class = MkdirLockFile
-
-        if lock_class is None:
-            lock_class = LockFile
+        try:
+            from lockfile import LockFile
+            from lockfile.mkdirlockfile import MkdirLockFile
+        except ImportError:
+            notice = dedent("""
+            NOTE: In order to use the FileCache you must have
+            lockfile installed. You can install it via pip:
+              pip install lockfile
+            """)
+            raise ImportError(notice)
+        else:
+            if use_dir_lock:
+                lock_class = MkdirLockFile
+
+            elif lock_class is None:
+                lock_class = LockFile
 
         self.directory = directory
         self.forever = forever
         self.filemode = filemode
         self.dirmode = dirmode
         self.lock_class = lock_class
 
-
     @staticmethod
     def encode(x):
         return hashlib.sha224(x.encode()).hexdigest()

tests/test_regressions.py

@@ -3,7 +3,7 @@
 
 
 from cachecontrol import CacheControl
-from cachecontrol.caches.file_cache import FileCache
+from cachecontrol.caches import FileCache
 from cachecontrol.filewrapper import CallbackFileWrapper
 from requests import Session