make python-magic optional, rely on builtin mimetypes module first

#116

setup.py

@@ -29,12 +29,15 @@ def main():
 
         python_requires='>=3.6',
         install_requires=[
-            *DEPS_INDEXER,
-            *DEPS_SERVER,
+            'appdirs', # for portable user directories detection
+            'tzlocal',
             'more_itertools',
             'pytz',
             'sqlalchemy', # DB api
             'cachew>=0.8.0', # caching with type hints
+
+            *DEPS_INDEXER,
+            *DEPS_SERVER,
         ],
         extras_require={
             'testing': [
@@ -61,17 +64,12 @@ def main():
         }
     )
 
+# todo might be nice to ensure they are installable in separation?
 DEPS_INDEXER = [
-    'appdirs', # for portable user directories detection
-
     'urlextract',
-
-    # TODO could be optional?
-    'python-magic', # for detecting mime types
 ]
 
 DEPS_SERVER = [
-    'tzlocal',
     'hug',
 ]
 
@@ -80,6 +78,7 @@ def main():
     # althrough server uses it so not sure...
     ('optional', 'dependencies that bring some bells & whistles'): [
         'logzero', # pretty colored logging
+        'python-magic', # better mimetype decetion
     ],
     ('HPI'     , 'dependencies for [[https://github.com/karlicoss/HPI][HPI]]'): [
         'HPI', # pypi version

src/promnesia/common.py

@@ -352,12 +352,37 @@ def python3() -> str:
 # ideally would be nice to fix it properly https://github.com/ahupp/python-magic#windows
 @lru_cache(1)
 def _magic():
-    import magic # type: ignore
-    return magic.Magic(mime=True)
+    logger = get_logger()
+    try:
+        import magic # type: ignore
+    except ModuleNotFoundError as me:
+        logger.exception(me)
+        msg = "python-magic is not detected. It's recommended for better file type detection (pip3 install --user python-magic). See https://github.com/ahupp/python-magic#installation"
+        logger.warning(msg)
+        warnings.warn(msg)
+        return lambda path: None # stub
+    else:
+        mm = magic.Magic(mime=True)
+        return mm.from_file
 
 
-def mime(path: PathIsh) -> str:
-    return _magic().from_file(str(path))
+@lru_cache(1)
+def _mimetypes():
+    import mimetypes
+    mimetypes.init()
+    return mimetypes
+
+
+def mime(path: PathIsh) -> Optional[str]:
+    ps = str(path)
+    mimetypes = _mimetypes()
+    # first try mimetypes, it's only using the filename without opening the file
+    pm, _ = mimetypes.guess_type(ps)
+    if pm is not None:
+        return pm
+    # next, libmagic, it might access the file, so a bit slower
+    magic = _magic()
+    return magic(ps)
 
 
 def find_args(root: Path, follow: bool) -> List[str]:

src/promnesia/sources/auto.py

@@ -252,25 +252,18 @@ def rit() -> Iterable[Path]:
                 yield from r
 
 
-import mimetypes
-mimetypes.init()
-
-
 def by_path(pp: Path):
     suf = pp.suffix.lower()
     # firt check suffixes, it's faster
     s = type2idx(suf)
     if s is not None:
         return s, None
-    # then try mimetypes, it's only using the filename
-    pm, _ = mimetypes.guess_type(str(pp))
-    if pm is not None:
-        s = type2idx(pm)
-        if s is not None:
-            return s, pm
-    # lastly, use libmagic, it's the slowest
+    # then try with mime
     pm = mime(pp)
-    return type2idx(pm), pm
+    if pm is not None:
+        return type2idx(pm), pm
+    else:
+        return None, None
 
 
 def _index_file(pp: Path, opts: Options) -> Results:

src/promnesia/sources/browser.py

@@ -6,7 +6,7 @@
 
 import pytz
 
-from ..common import PathIsh, Results, Visit, Loc, get_logger, Second, _magic
+from ..common import PathIsh, Results, Visit, Loc, get_logger, Second, mime
 from .. import config
 
 # todo mcachew?
@@ -16,12 +16,11 @@
 
 
 def index(p: PathIsh) -> Results:
-    mime = _magic()
     pp = Path(p)
     assert pp.exists() # just in case of broken symlinks
 
     # is_file check because it also returns dirs
-    is_db = lambda x: x.is_file() and mime.from_file(str(x)) in ['application/x-sqlite3']
+    is_db = lambda x: x.is_file() and mime(x) in ['application/x-sqlite3']
 
     # todo warn if filtered out too many?
     # todo wonder how quickly mimes can be computed?