backend: Add random option

pywal/__main__.py

@@ -38,12 +38,13 @@ def get_args(args):
                      help="Custom background color to use.")
 
     arg.add_argument("--backend", metavar="backend",
-                     help="Which color backend to use.",
+                     help="Which color backend to use. \
+                           Use 'wal --backend' to list backends.",
                      const="list_backends", type=str, nargs="?", default="wal")
 
     arg.add_argument("--theme", metavar="/path/to/file or theme_name",
                      help="Which colorscheme file to use. \
-                           Use 'wal -f' to list available builtin themes.",
+                           Use 'wal --theme' to list builtin themes.",
                      const="list_themes", nargs="?")
 
     arg.add_argument("-c", action="store_true",

pywal/colors.py

@@ -2,6 +2,7 @@
 Generate a palette using various backends.
 """
 import os
+import random
 import re
 import sys
 
@@ -94,6 +95,13 @@ def get(img, light=False, backend="wal", cache_dir=CACHE_DIR):
     else:
         print("wal: Generating a colorscheme...")
 
+        if backend == "random":
+            backends = list_backends()
+            random.shuffle(backends)
+            backend = backends[0]
+
+        print("wal: Using", backend, "backend.")
+
         # Dynamically import the backend we want to use.
         # This keeps the dependencies "optional".
         try: