fix isatty parameter behaviour xolox#84

coloredlogs/__init__.py

@@ -424,13 +424,13 @@ def install(level=None, **kw):
                 # represent a logging level for system logging.
                 enable_system_logging(level=syslog_enabled)
         # Figure out whether we can use ANSI escape sequences.
-        use_colors = kw.get('isatty', None)
-        if use_colors or use_colors is None:
+        use_colors = orig_use_colors = kw.get('isatty', None)
+        if use_colors or orig_use_colors is None:
             # Try to enable Windows native ANSI support or Colorama.
             if on_windows():
                 use_colors = enable_ansi_support()
             # Disable ANSI escape sequences if 'stream' isn't connected to a terminal.
-            if use_colors or use_colors is None:
+            if orig_use_colors is None:
                 use_colors = terminal_supports_colors(stream)
         # Create a stream handler.
         handler = logging.StreamHandler(stream) if stream else StandardErrorHandler()