Do not import ecmwf-api-client for standalone MARS access (#489)

* Do not import ecmwf-api-client for standalone MARS access

docs/release_notes/version_0.10_updates.rst

@@ -1,6 +1,16 @@
 Version 0.10 Updates
 /////////////////////////
 
+
+Version 0.10.8
+===============
+
+Fixes
+++++++
+
+- Fixed issue when tried to import "ecmwf-api-client" unnecessarily when the standalone MARS client was invoked for retrieving data from MARS.
+
+
 Version 0.10.7
 ===============
 

src/earthkit/data/sources/mars.py

@@ -11,11 +11,6 @@
 import os
 import subprocess
 
-try:
-    import ecmwfapi
-except ImportError:
-    raise ImportError("MARS access requires 'ecmwf-api-client' to be installed")
-
 from earthkit.data.core.settings import SETTINGS
 from earthkit.data.core.temporary import temp_file
 
@@ -49,13 +44,24 @@ def execute(self, request, target):
                 check=True,
             )
 
+    @staticmethod
+    def enabled():
+        if SETTINGS.get("use-standalone-mars-client-when-available"):
+            return os.path.exists(StandaloneMarsClient.EXE)
+        return False
+
 
 class MarsRetriever(ECMWFApi):
     def service(self):
         if SETTINGS.get("use-standalone-mars-client-when-available"):
             if os.path.exists(StandaloneMarsClient.EXE):
                 return StandaloneMarsClient()
 
+        try:
+            import ecmwfapi
+        except ImportError:
+            raise ImportError("MARS access requires 'ecmwf-api-client' to be installed")
+
         if self.prompt:
             prompt = MARSAPIKeyPrompt()
             prompt.check()

src/earthkit/data/testing.py

@@ -18,6 +18,7 @@
 from earthkit.data import from_source
 from earthkit.data.readers.text import TextReader
 from earthkit.data.sources.empty import EmptySource
+from earthkit.data.sources.mars import StandaloneMarsClient
 
 LOG = logging.getLogger(__name__)
 
@@ -90,7 +91,10 @@ def modules_installed(*modules):
     return True
 
 
-NO_MARS = not os.path.exists(os.path.expanduser("~/.ecmwfapirc"))
+NO_MARS_DIRECT = not StandaloneMarsClient.enabled()
+NO_MARS_API = not os.path.exists(os.path.expanduser("~/.ecmwfapirc"))
+NO_MARS = NO_MARS_API and NO_MARS_DIRECT
+
 NO_CDS = not os.path.exists(os.path.expanduser("~/.cdsapirc"))
 NO_HDA = not os.path.exists(os.path.expanduser("~/.hdarc"))
 IN_GITHUB = os.environ.get("GITHUB_WORKFLOW") is not None