MAINT: do not import linkahead during build

setup.py

@@ -4,6 +4,7 @@
 #
 """linkahead"""
 import os
+import re
 import subprocess
 import sys
 
@@ -103,12 +104,13 @@ def get_version_info():
             GIT_REVISION = f.read().strip()
     elif os.path.exists('src/linkahead/version.py'):
         # must be a source distribution, use existing version file
-        try:
-            from linkahead.version import git_revision as GIT_REVISION
-        except ImportError:
-            raise ImportError("Unable to import git_revision. Try removing "
-                              "src/linkahead/version.py and the build directory "
-                              "before building.")
+        with open('src/linkahead/version.py') as fi:
+            for line in fi.readlines():
+                match = re.match(r"^git_revision = (?P<rev>.*)$", line)
+
+                if match is not None:
+                    GIT_REVISION = match.group('rev')
+
     else:
         GIT_REVISION = "Unknown"