From 69c1a8e2acf388154dec68d4087ff48802036da5 Mon Sep 17 00:00:00 2001
From: Zhiwei Liang <zhiwei@sinatra.ai>
Date: Tue, 13 Jul 2021 12:48:28 -0700
Subject: [PATCH] Improve copy method in blueprint, adding possibiliy to keep
 original attribute values.

---
 sanic/blueprints.py | 33 +++++++++++++++++++++++++--------
 sanic/helpers.py    | 14 ++++++++++++++
 2 files changed, 39 insertions(+), 8 deletions(-)

diff --git a/sanic/blueprints.py b/sanic/blueprints.py
index 5238f1ba..fea4c84e 100644
--- a/sanic/blueprints.py
+++ b/sanic/blueprints.py
@@ -13,6 +13,7 @@ from sanic_routing.route import Route  # type: ignore
 from sanic.base import BaseSanic
 from sanic.blueprint_group import BlueprintGroup
 from sanic.exceptions import SanicException
+from sanic.helpers import _default
 from sanic.models.futures import FutureRoute, FutureStatic
 from sanic.models.handler_types import (
     ListenerType,
@@ -148,17 +149,33 @@ class Blueprint(BaseSanic):
     def copy(
         self,
         name: str,
-        url_prefix: str = "",
-        version: Optional[Union[int, str, float]] = None,
-        strict_slashes: Optional[bool] = None,
-        version_prefix: str = "/v",
+        url_prefix: str = _default,
+        version: Optional[Union[int, str, float]] = _default,
+        version_prefix: str = _default,
+        strict_slashes: Optional[bool] = _default,
     ):
+        """
+        Copy a blueprint instance with some optional parameters to 
+        override the values of attributes in the old instance.
+
+        :param name: unique name of the blueprint
+        :param url_prefix: URL to be prefixed before all route URLs
+        :param host: IP Address of FQDN for the sanic server to use.
+        :param version: Blueprint Version
+        :param version_prefix: the prefix of the version number shown in the URL.
+        :param strict_slashes: Enforce the API urls are requested with a
+            training */*
+        """
         new_bp = deepcopy(self)
         new_bp.name = name
-        new_bp.url_prefix = url_prefix
-        new_bp.version = version
-        new_bp.strict_slashes = strict_slashes
-        new_bp.version_prefix = version_prefix
+        if url_prefix != _default:
+            new_bp.url_prefix = url_prefix
+        if version != _default:
+            new_bp.version = version
+        if strict_slashes != _default:
+            new_bp.strict_slashes = strict_slashes
+        if version_prefix != _default:
+            new_bp.version_prefix = version_prefix
 
         return new_bp
 
diff --git a/sanic/helpers.py b/sanic/helpers.py
index 15ae7bf2..87d51b53 100644
--- a/sanic/helpers.py
+++ b/sanic/helpers.py
@@ -155,3 +155,17 @@ def import_string(module_name, package=None):
     if ismodule(obj):
         return obj
     return obj()
+
+
+class Default:
+    """
+    It is used to replace `None` or `object()` as a sentinel
+    that represents a default value. Sometimes we want to set
+    a value to `None` so we cannot use `None` to represent the
+    default value, and `object()` is hard to be typed.
+    """
+
+    pass
+
+
+_default = Default()