patman: Use ANSI colours only when outputting to a terminal

It is easy to detect whether or not the process is connected to a terminal,
or piped to a file. Disable ANSI colours automatically when output is
not to a terminal.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/patman/terminal.py

@@ -24,6 +24,12 @@
 This module handles terminal interaction including ANSI color codes.
 """
 
+import os
+import sys
+
+# Selection of when we want our output to be colored
+COLOR_IF_TERMINAL, COLOR_ALWAYS, COLOR_NEVER = range(3)
+
 class Color(object):
   """Conditionally wraps text in ANSI color escape sequences."""
   BLACK, RED, GREEN, YELLOW, BLUE, MAGENTA, CYAN, WHITE = range(8)
@@ -32,14 +38,15 @@ class Color(object):
   BOLD_START = '\033[1m'
   RESET = '\033[0m'
 
-  def __init__(self, enabled=True):
+  def __init__(self, colored=COLOR_IF_TERMINAL):
     """Create a new Color object, optionally disabling color output.
 
     Args:
       enabled: True if color output should be enabled. If False then this
         class will not add color codes at all.
     """
-    self._enabled = enabled
+    self._enabled = (colored == COLOR_ALWAYS or
+        (colored == COLOR_IF_TERMINAL and os.isatty(sys.stdout.fileno())))
 
   def Start(self, color):
     """Returns a start color code.