diff --git a/scrapy/robotstxt.py b/scrapy/robotstxt.py
index ad06137e2..a33f73306 100644
--- a/scrapy/robotstxt.py
+++ b/scrapy/robotstxt.py
@@ -3,9 +3,10 @@ from __future__ import annotations
 import logging
 import sys
 from abc import ABCMeta, abstractmethod
-from typing import TYPE_CHECKING, Union
+from typing import TYPE_CHECKING, Optional, Union
 from warnings import warn
 
+from scrapy import Spider
 from scrapy.exceptions import ScrapyDeprecationWarning
 from scrapy.utils.python import to_unicode
 
@@ -18,12 +19,14 @@ if TYPE_CHECKING:
 logger = logging.getLogger(__name__)
 
 
-def decode_robotstxt(robotstxt_body, spider, to_native_str_type=False):
+def decode_robotstxt(
+    robotstxt_body: bytes, spider: Optional[Spider], to_native_str_type: bool = False
+) -> str:
     try:
         if to_native_str_type:
-            robotstxt_body = to_unicode(robotstxt_body)
+            body_decoded = to_unicode(robotstxt_body)
         else:
-            robotstxt_body = robotstxt_body.decode("utf-8", errors="ignore")
+            body_decoded = robotstxt_body.decode("utf-8", errors="ignore")
     except UnicodeDecodeError:
         # If we found garbage or robots.txt in an encoding other than UTF-8, disregard it.
         # Switch to 'allow all' state.
@@ -33,8 +36,8 @@ def decode_robotstxt(robotstxt_body, spider, to_native_str_type=False):
             exc_info=sys.exc_info(),
             extra={"spider": spider},
         )
-        robotstxt_body = ""
-    return robotstxt_body
+        body_decoded = ""
+    return body_decoded
 
 
 class RobotParser(metaclass=ABCMeta):
@@ -66,82 +69,80 @@ class RobotParser(metaclass=ABCMeta):
 
 
 class PythonRobotParser(RobotParser):
-    def __init__(self, robotstxt_body, spider):
+    def __init__(self, robotstxt_body: bytes, spider: Optional[Spider]):
         from urllib.robotparser import RobotFileParser
 
-        self.spider = spider
-        robotstxt_body = decode_robotstxt(
-            robotstxt_body, spider, to_native_str_type=True
-        )
-        self.rp = RobotFileParser()
-        self.rp.parse(robotstxt_body.splitlines())
+        self.spider: Optional[Spider] = spider
+        body_decoded = decode_robotstxt(robotstxt_body, spider, to_native_str_type=True)
+        self.rp: RobotFileParser = RobotFileParser()
+        self.rp.parse(body_decoded.splitlines())
 
     @classmethod
-    def from_crawler(cls, crawler, robotstxt_body):
+    def from_crawler(cls, crawler: Crawler, robotstxt_body: bytes) -> Self:
         spider = None if not crawler else crawler.spider
         o = cls(robotstxt_body, spider)
         return o
 
-    def allowed(self, url, user_agent):
+    def allowed(self, url: Union[str, bytes], user_agent: Union[str, bytes]) -> bool:
         user_agent = to_unicode(user_agent)
         url = to_unicode(url)
         return self.rp.can_fetch(user_agent, url)
 
 
 class ReppyRobotParser(RobotParser):
-    def __init__(self, robotstxt_body, spider):
+    def __init__(self, robotstxt_body: bytes, spider: Optional[Spider]):
         warn("ReppyRobotParser is deprecated.", ScrapyDeprecationWarning, stacklevel=2)
         from reppy.robots import Robots
 
-        self.spider = spider
+        self.spider: Optional[Spider] = spider
         self.rp = Robots.parse("", robotstxt_body)
 
     @classmethod
-    def from_crawler(cls, crawler, robotstxt_body):
+    def from_crawler(cls, crawler: Crawler, robotstxt_body: bytes) -> Self:
         spider = None if not crawler else crawler.spider
         o = cls(robotstxt_body, spider)
         return o
 
-    def allowed(self, url, user_agent):
+    def allowed(self, url: Union[str, bytes], user_agent: Union[str, bytes]) -> bool:
         return self.rp.allowed(url, user_agent)
 
 
 class RerpRobotParser(RobotParser):
-    def __init__(self, robotstxt_body, spider):
+    def __init__(self, robotstxt_body: bytes, spider: Optional[Spider]):
         from robotexclusionrulesparser import RobotExclusionRulesParser
 
-        self.spider = spider
-        self.rp = RobotExclusionRulesParser()
-        robotstxt_body = decode_robotstxt(robotstxt_body, spider)
-        self.rp.parse(robotstxt_body)
+        self.spider: Optional[Spider] = spider
+        self.rp: RobotExclusionRulesParser = RobotExclusionRulesParser()
+        body_decoded = decode_robotstxt(robotstxt_body, spider)
+        self.rp.parse(body_decoded)
 
     @classmethod
-    def from_crawler(cls, crawler, robotstxt_body):
+    def from_crawler(cls, crawler: Crawler, robotstxt_body: bytes) -> Self:
         spider = None if not crawler else crawler.spider
         o = cls(robotstxt_body, spider)
         return o
 
-    def allowed(self, url, user_agent):
+    def allowed(self, url: Union[str, bytes], user_agent: Union[str, bytes]) -> bool:
         user_agent = to_unicode(user_agent)
         url = to_unicode(url)
         return self.rp.is_allowed(user_agent, url)
 
 
 class ProtegoRobotParser(RobotParser):
-    def __init__(self, robotstxt_body, spider):
+    def __init__(self, robotstxt_body: bytes, spider: Optional[Spider]):
         from protego import Protego
 
-        self.spider = spider
-        robotstxt_body = decode_robotstxt(robotstxt_body, spider)
-        self.rp = Protego.parse(robotstxt_body)
+        self.spider: Optional[Spider] = spider
+        body_decoded = decode_robotstxt(robotstxt_body, spider)
+        self.rp = Protego.parse(body_decoded)
 
     @classmethod
-    def from_crawler(cls, crawler, robotstxt_body):
+    def from_crawler(cls, crawler: Crawler, robotstxt_body: bytes) -> Self:
         spider = None if not crawler else crawler.spider
         o = cls(robotstxt_body, spider)
         return o
 
-    def allowed(self, url, user_agent):
+    def allowed(self, url: Union[str, bytes], user_agent: Union[str, bytes]) -> bool:
         user_agent = to_unicode(user_agent)
         url = to_unicode(url)
         return self.rp.can_fetch(url, user_agent)