Merge pull request #151 from Ouranosinc/esmpy-guess-esmfmk

[ESMpy] Guess esmf.mk locations
Contribution authored by: aulemahal

src/addon/esmpy/doc/install.rst

@@ -62,15 +62,7 @@ Installing ESMPy from Source
 ----------------------------
 
 When installing from source, ESMPy uses `pip <https://pypi.org/project/pip//>`_ 
-to build and install the package. This requires setting an environment variable 
-pointing to a file named esmf.mk that is generated during an ESMF installation.  
-The path of this file is:
-
-.. code::
-
-    <ESMF_INSTALL_DIR>/lib/lib<g<or>O>/<platform>/esmf.mk
-
-An installation of ESMPy in the default location for Python packages can be done
+to build and install the package. An installation of ESMPy in the default location for Python packages can be done
 with the following command issued from the top level ESMPy directory (``src/addon/esmpy``):
 
 .. code::
@@ -93,7 +85,8 @@ To use ESMPy in an external program, import it with:
 
     import esmpy
 
-The environment variable ``ESMFMKFILE`` must be set when using ESMPy.
+The environment variable ``ESMFMKFILE`` should be set when using ESMPy. If it is not found, the package will
+try to guess a few very common locations, but we recommend correctly setting the variable nonetheless.
 
 .. Note::
 

src/addon/esmpy/src/esmpy/interface/loadESMF.py

@@ -24,8 +24,18 @@
 esmfmk = None
 try:
     esmfmk = os.environ["ESMFMKFILE"]
-except:
-    raise ImportError('The ESMFMKFILE environment variable is not available.')
+except KeyError:
+    # Try to guess with very common paths in normal installs (especially conda)
+    guesses = [
+        os.path.join(sys.prefix, 'lib', 'esmf.mk'),  # conda build of esmf
+        os.path.join(sys.prefix, 'Library', 'lib', 'esmf.mk')
+    ]
+    for path in guesses:
+        if os.path.isfile(path):
+            esmfmk = path
+            break
+    else:
+        raise ImportError('The esmf.mk file cannot be found. Pass its path in the ESMFMKFILE environment variable.')
 
 #### INVESTIGATE esmf.mk ######################################################