Fix ./hooks/pre_gen_project.py asking user to select an option once only

+ prettify output

hooks/pre_gen_project.py

@@ -1,27 +1,50 @@
 project_slug = '{{ cookiecutter.project_slug }}'
-
 if hasattr(project_slug, 'isidentifier'):
-    assert project_slug.isidentifier(), 'Project slug should be valid Python identifier!'
+    assert project_slug.isidentifier(), "'{}' project slug is not a valid Python identifier.".format(project_slug)
 
-heroku = '{{ cookiecutter.use_heroku }}'.lower()
-docker = '{{ cookiecutter.use_docker }}'.lower()
+using_docker = '{{ cookiecutter.use_docker }}'.lower()
+if using_docker == 'n':
+    TERMINATOR = "\x1b[0m"
+    WARNING = "\x1b[1;33m [WARNING]: "
+    INFO = "\x1b[1;33m [INFO]: "
+    HINT = "\x1b[3;33m"
+    SUCCESS = "\x1b[1;32m [SUCCESS]: "
 
-if docker == 'n':
-	import sys
+    import sys
 
-	python_major_version = sys.version_info[0]
+    python_major_version = sys.version_info[0]
+    if python_major_version == 2:
+        sys.stdout.write(
+            WARNING +
+            "Cookiecutter Django does not support Python 2. "
+            "Stability is guaranteed with Python 3.6+ only, "
+            "are you sure you want to proceed (y/n)? " +
+            TERMINATOR
+        )
+        yes_options, no_options = frozenset(['y']), frozenset(['n'])
+        while True:
+            choice = raw_input().lower()
+            if choice in yes_options:
+                break
+            elif choice in no_options:
+                sys.stdout.write(
+                    INFO +
+                    "Generation process stopped as requested." +
+                    TERMINATOR
+                )
+                sys.exit(0)
+            else:
+                sys.stdout.write(
+                    HINT +
+                    "Please respond with {} or {}: ".format(
+                        ', '.join(["'{}'".format(o) for o in yes_options if not o == '']),
+                        ', '.join(["'{}'".format(o) for o in no_options if not o == ''])
+                    ) +
+                    TERMINATOR
+                )
 
-	if python_major_version == 2:
-		sys.stdout.write("WARNING: Cookiecutter Django does not support Python 2! Stability is guaranteed with Python 3.4+ only. Are you sure you want to proceed? (y/n)")
-
-		yes_options = set(['y'])
-		no_options = set(['n', ''])
-		choice = raw_input().lower()
-		if choice in no_options:
-			sys.exit(1)
-		elif choice in yes_options:
-			pass
-		else:
-			sys.stdout.write("Please respond with %s or %s"
-				% (', '.join([o for o in yes_options if not o == ''])
-					, ', '.join([o for o in no_options if not o == ''])))
+    sys.stdout.write(
+        SUCCESS +
+        "Project initialized, keep up the good work!" +
+        TERMINATOR
+    )