# subst_vars ()
+def grok_environment_error (exc, prefix="error: "):
+ """Generate a useful error message from an EnvironmentError (IOError or
+ OSError) exception object. Handles Python 1.5.1 and 1.5.2 styles, and
+ does what it can to deal with exception objects that don't have a
+ filename (which happens when the error is due to a two-file operation,
+ such as 'rename()' or 'link()'. Returns the error message as a string
+ prefixed with 'prefix'.
+ """
+ # check for Python 1.5.2-style {IO,OS}Error exception objects
+ if hasattr (exc, 'filename') and hasattr (exc, 'strerror'):
+ if exc.filename:
+ error = prefix + "%s: %s" % (exc.filename, exc.strerror)
+ else:
+ # two-argument functions in posix module don't
+ # include the filename in the exception object!
+ error = prefix + "%s" % exc.strerror
+ else:
+ error = prefix + str(exc[-1])
+
+ return error