Add color utility.

pre_commit/color.py

@@ -0,0 +1,32 @@
+
+import sys
+
+RED = '\033[41m'
+GREEN = '\033[42m'
+NORMAL = '\033[0m'
+
+
+def format_color(text, color, use_color):
+    """Format text with color.
+
+    Args:
+        text - Text to be formatted with color if `use_color`
+        color - The color start string
+        use_color - Whether or not to color
+    """
+    if not use_color:
+        return text
+    else:
+        return u'{0}{1}{2}'.format(color, text, NORMAL)
+
+
+def use_color(setting):
+    """Choose whether to use color based on the command argument.
+
+    Args:
+        setting - Either `auto`, `always`, or `never`
+    """
+    return (
+        setting == 'always' or
+        (setting == 'auto' and sys.stdout.isatty())
+    )