Get auto-version setting right

Fixes #30

Author: gordonwatts

.vscode/settings.json

@@ -16,18 +16,23 @@
         "elts",
         "firstlineno",
         "funcs",
+        "getenv",
         "inuse",
         "jetpt",
         "mult",
         "nogood",
         "numpy",
         "obj's",
+        "prereleased",
         "ptgev",
+        "pypa",
+        "pypi",
         "pytest",
         "reco",
         "rmul",
         "rsub",
         "rtruediv",
+        "sdist",
         "setuptools",
         "subexpr",
         "ufunc",

setup.py

@@ -1,11 +1,19 @@
 # Need setuptools even though it isn't used - loads some plugins.
 from setuptools import find_packages  # noqa: F401
 from distutils.core import setup
+import os
 
 # Use the readme as the long description.
 with open("README.md", "r") as fh:
     long_description = fh.read()
 
+
+version = os.getenv('dataframe_expressions_version')
+if version is None:
+    version = '0.1a1'
+else:
+    version = version.split('/')[-1]
+
 extras_require = {'test': ['pytest', 'pytest-asyncio', 'pytest-cov',
                            'flake8', 'coverage', 'twine', 'wheel', 'numpy']}
 extras_require['complete'] = sorted(set(sum(extras_require.values(), [])))