Make client_info work without gRPC installed. (#5075)

1 files changed, 14 insertions, 6 deletions

diff --git a/google/api_core/gapic_v1/client_info.py b/google/api_core/gapic_v1/client_info.py
index a76754d..7feeaf1 100644
--- a/google/api_core/gapic_v1/client_info.py
+++ b/google/api_core/gapic_v1/client_info.py
@@ -23,8 +23,13 @@ import platform
 import pkg_resources
 
 _PY_VERSION = platform.python_version()
-_GRPC_VERSION = pkg_resources.get_distribution('grpcio').version
 _API_CORE_VERSION = pkg_resources.get_distribution('google-api-core').version
+
+try:
+    _GRPC_VERSION = pkg_resources.get_distribution('grpcio').version
+except pkg_resources.DistributionNotFound:  # pragma: NO COVER
+    _GRPC_VERSION = None
+
 METRICS_METADATA_KEY = 'x-goog-api-client'
 
 
@@ -38,7 +43,7 @@ class ClientInfo(object):
     Args:
         python_version (str): The Python interpreter version, for example,
             ``'2.7.13'``.
-        grpc_version (str): The gRPC library version.
+        grpc_version (Optional[str]): The gRPC library version.
         api_core_version (str): The google-api-core library version.
         gapic_version (Optional[str]): The sversion of gapic-generated client
             library, if the library was generated by gapic.
@@ -66,15 +71,18 @@ class ClientInfo(object):
         # expects these items to be in specific locations.
         ua = 'gl-python/{python_version} '
 
-        if self.client_library_version is not None:
-            ua += 'gccl/{client_library_version} '
+        if self.grpc_version is not None:
+            ua += 'grpc/{grpc_version} '
+
+        ua += 'gax/{api_core_version} '
 
         if self.gapic_version is not None:
             ua += 'gapic/{gapic_version} '
 
-        ua += 'gax/{api_core_version} grpc/{grpc_version}'
+        if self.client_library_version is not None:
+            ua += 'gccl/{client_library_version} '
 
-        return ua.format(**self.__dict__)
+        return ua.format(**self.__dict__).strip()
 
     def to_grpc_metadata(self):
         """Returns the gRPC metadata for this client info."""