Raise a warning when importing py2opsin if Java is not installed (#11)

README.md

@@ -14,7 +14,7 @@
 </p> 
 
 ## Installation
-`py2opsin` can be installed with `pip install py2opsin`. It has _zero_ dependencies (`OPSIN v2.7.0` is included in the PyPI package) and should work inside any environment running modern Python.
+`py2opsin` can be installed with `pip install py2opsin`. It has _zero_ Python dependencies (`OPSIN v2.7.0` is included in the PyPI package) and should work inside any environment running modern Python. Java 8+ is required to run OPSIN.
 
 Try a demo of `py2opsin` live on your browser (no installation required!): [![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/JacksonBurns/py2opsin/HEAD?labpath=examples%2Fpy2opsin_example.ipynb)
 

py2opsin/__init__.py

@@ -1,3 +1,3 @@
 from .py2opsin import py2opsin
 
-__version__ = "1.0.3"
+__version__ = "1.0.4"

py2opsin/py2opsin.py

@@ -4,6 +4,7 @@
 import warnings
 from difflib import get_close_matches
 from typing import Union
+from subprocess import CalledProcessError
 
 try:
     from importlib.resources import files
@@ -14,6 +15,21 @@
 
     pkg_fopen = lambda fname: resource_filename(__name__, fname)
 
+# check if java is installed
+try:
+    result = subprocess.run(
+        ["java", "-version"],
+        stdout=subprocess.DEVNULL,
+        stderr=subprocess.DEVNULL,
+        check=True,
+    )
+except Exception as e:
+    warnings.warn(
+        "Java may not be installed/accessible (java -version raised exception). "
+        "Java 8 or newer is required to use py2opsin. Original Error:\n" + repr(e),
+        category=RuntimeWarning,
+    )
+
 
 def py2opsin(
     chemical_name: Union[str, list],
@@ -37,8 +53,9 @@ def py2opsin(
         jar_fpath (str, optional): Filepath to OPSIN jar file. Defaults to "default", which causes py2opsin to use its included jar.
 
     Returns:
-        str: Species in requested format, or False if not found or an error occoured. List of strings if input is list.
+        str: Species in requested format, or False if not found or an error ocurred. List of strings if input is list.
     """
+    # path to OPSIN jar
     if jar_fpath == "default":
         jar_fpath = pkg_fopen("opsin-cli-2.7.0-jar-with-dependencies.jar")
 
@@ -134,7 +151,7 @@ def py2opsin(
             )
 
     except Exception as e:
-        warnings.warn("Unexpected error occured! " + e)
+        warnings.warn("Unexpected error ocurred! " + e)
         return False
     finally:
         os.remove(temp_f)