Adds _marker attribute to HostKeyEntry

* Adds some type annotations
* Includes _marker in the output of `to_line`
* Sets _marker when constructing `HostKeyEntry` in `from_line`

paramiko/hostkeys.py

@@ -19,6 +19,7 @@
 
 from base64 import encodebytes, decodebytes
 from enum import Enum
+from typing import Iterable, Optional
 import binascii
 import os
 import re
@@ -177,9 +178,7 @@ def __setitem__(self, key, val):
 
             def keys(self):
                 return [
-                    e.key.get_name()
-                    for e in self._entries
-                    if e.key is not None
+                    e.key.get_name() for e in self._entries if e.key is not None
                 ]
 
         entries = []
@@ -322,13 +321,19 @@ class HostKeyEntry:
     Representation of a line in an OpenSSH-style "known hosts" file.
     """
 
-    def __init__(self, hostnames=None, key=None):
+    def __init__(
+        self,
+        hostnames: Optional[Iterable[str]] = None,
+        key: Optional[PKey] = None,
+        marker: Optional[HostKeyMarkers] = None,
+    ):
         self.valid = (hostnames is not None) and (key is not None)
         self.hostnames = hostnames
         self.key = key
+        self._marker = marker
 
     @classmethod
-    def from_line(cls, line, lineno=None):
+    def from_line(cls, line: str, lineno: Optional[int] = None):
         """
         Parses the given line of text to find the names for the host,
         the type of key, and the key data. The line is expected to be in the
@@ -340,6 +345,7 @@ def from_line(cls, line, lineno=None):
         that should be taken care of before sending the line to us.
 
         :param str line: a line from an OpenSSH known_hosts file
+        :param int|None lineno: the line number on which the entry appears
         """
         log = get_logger("paramiko.hostkeys")
         fields = re.split(" |\t", line)
@@ -375,7 +381,9 @@ def from_line(cls, line, lineno=None):
             raise InvalidHostKey(line, e)
 
         try:
-            return cls(names, PKey.from_type_string(key_type, key_bytes))
+            return cls(
+                names, PKey.from_type_string(key_type, key_bytes), marker=marker
+            )
         except UnknownKeyType:
             # TODO 4.0: consider changing HostKeys API so this just raises
             # naturally and the exception is muted higher up in the stack?
@@ -389,6 +397,13 @@ def to_line(self):
         included.
         """
         if self.valid:
+            if self._marker:
+                return "{} {} {} {}\n".format(
+                    self._marker.value,
+                    ",".join(self.hostnames),
+                    self.key.get_name(),
+                    self.key.get_base64(),
+                )
             return "{} {} {}\n".format(
                 ",".join(self.hostnames),
                 self.key.get_name(),