Fix requirement being used before installing

setup.py

@@ -1,6 +1,5 @@
 from setuptools import setup, find_packages
-
-from ufpy import __version__
+import re
 
 with open('README.md', 'r', encoding='utf-8') as mdf:
     long_description = mdf.read()
@@ -15,6 +14,33 @@
 project_name = 'ufpy'
 github_url = f'https://github.com/{organization_name}/{project_name}'
 
+def derive_version() -> str: # this function is stolen from discord.py
+    version = ''
+    with open('ufpy/__init__.py') as f:
+        version = re.search(r'^__version__\s*=\s*[\'"]([^\'"]*)[\'"]', f.read(), re.MULTILINE).group(1)
+
+    if not version:
+        raise RuntimeError('version is not set')
+
+    if version.endswith(('a', 'b', 'rc')):
+        # append version identifier based on commit count
+        try:
+            import subprocess
+
+            p = subprocess.Popen(['git', 'rev-list', '--count', 'HEAD'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+            out, err = p.communicate()
+            if out:
+                version += out.decode('utf-8').strip()
+            p = subprocess.Popen(['git', 'rev-parse', '--short', 'HEAD'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+            out, err = p.communicate()
+            if out:
+                version += '+g' + out.decode('utf-8').strip()
+        except Exception:
+            pass
+
+    return version
+
+__version__ = derive_version()
 
 setup(
     name=project_name,