Only import compiler when necessary, it's not available in 3.x.

mitogen/master.py

-try:
-    import ast
-except ImportError:
-    # ast module is not available in Python 2.4.x, instead we shall use the
-    # the compiler module as a fallback
-    ast = None
 import commands
-import compiler
 import errno
 import getpass
 import imp
@@ -27,6 +20,14 @@ import time
 import types
 import zlib
 
+try:
+    import ast
+except ImportError:
+    # ast module is not available in Python 2.4.x, instead we shall use the the
+    # compiler module as a fallback
+    ast = None
+    import compiler
+
 if not hasattr(pkgutil, 'find_loader'):
     # find_loader() was new in >=2.5, but the modern pkgutil.py syntax has
     # been kept intentionally 2.3 compatible so we can reuse it.