[svn r57565] also introduce config.maketrace(name, flush=False) which

returns either a nulltracer or opens a log in the tracedir
and returns an object that you can call with args to print
into the file.

--HG--
branch : trunk

py/test/config.py

@@ -226,6 +226,33 @@ class Config(object):
         if self.option.tracedir is not None:
             return py.path.local(self.option.tracedir)
 
+    def maketrace(self, name, flush=False):
+        """ return a tracedirectory or None, depending on --tracedir. """
+        tracedir = self.gettracedir()
+        if tracedir is None:
+            return NullTracer()
+        return Tracer(tracedir.join(name), flush=flush)
+
+class Tracer(object):
+    file = None
+    def __init__(self, path, flush=False):
+        self.file = path.open(mode='w')
+        self.flush = flush
+       
+    def __call__(self, *args):
+        print >>self.file, " ".join(map(str, args))
+        if self.flush:
+            self.file.flush()
+
+    def close(self):
+        self.file.close()
+
+class NullTracer:
+    def __call__(self, *args):
+        pass
+    def close(self):
+        pass
+    
 # this is the one per-process instance of py.test configuration 
 config_per_process = Config()