UDPipe (and thus ufal.udpipe) doesn't need to be imported if online=1

Author: michnov

udapi/block/udpipe/base.py

@@ -1,9 +1,15 @@
 """Block udpipe.Base for tagging and parsing using UDPipe."""
 from udapi.core.block import Block
-from udapi.tool.udpipe import UDPipe
 from udapi.tool.udpipeonline import UDPipeOnline
 from udapi.core.bundle import Bundle
 
+# Import UDPipe only if available (requires ufal.udpipe)
+try:
+    from udapi.tool.udpipe import UDPipe
+    UDPIPE_AVAILABLE = True
+except ImportError:
+    UDPIPE_AVAILABLE = False
+
 KNOWN_MODELS = {
     'af': 'models/udpipe/2.4/afrikaans-afribooms-ud-2.4-190531.udpipe',
     'af_afribooms': 'models/udpipe/2.4/afrikaans-afribooms-ud-2.4-190531.udpipe',
@@ -143,6 +149,8 @@ def tool(self):
         if self.online:
             self._tool = UDPipeOnline(model=self.model)
         else:
+            if not UDPIPE_AVAILABLE:
+                raise ImportError("UDPipe is not available. Install ufal.udpipe or use online=1")
             self._tool = UDPipe(model=self.model)
         return self._tool