diff --git a/mitmproxy/addons/core.py b/mitmproxy/addons/core.py
index b0d8ee275..33d672790 100644
--- a/mitmproxy/addons/core.py
+++ b/mitmproxy/addons/core.py
@@ -112,7 +112,7 @@ class Core:
         val = sval  # type: typing.Union[int, str]
         if spec == "status_code":
             try:
-                val = int(val)
+                val = int(val)  # type: ignore
             except ValueError as v:
                 raise exceptions.CommandError(
                     "Status code is not an integer: %s" % val
@@ -145,7 +145,7 @@ class Core:
                 if spec == "status_code":
                     resp.status_code = val
                     if val in status_codes.RESPONSES:
-                        resp.reason = status_codes.RESPONSES[int(val)]
+                        resp.reason = status_codes.RESPONSES[val]  # type: ignore
                 elif spec == "reason":
                     resp.reason = val
                 else:
diff --git a/mitmproxy/eventsequence.py b/mitmproxy/eventsequence.py
index 4e1999726..d263727b7 100644
--- a/mitmproxy/eventsequence.py
+++ b/mitmproxy/eventsequence.py
@@ -1,4 +1,7 @@
+import typing
+
 from mitmproxy import controller
+from mitmproxy import flow
 from mitmproxy import http
 from mitmproxy import tcp
 from mitmproxy import websocket
@@ -8,27 +11,26 @@ Events = frozenset([
     "clientdisconnect",
     "serverconnect",
     "serverdisconnect",
-
+    # TCP
     "tcp_start",
     "tcp_message",
     "tcp_error",
     "tcp_end",
-
+    # HTTP
     "http_connect",
     "request",
     "requestheaders",
     "response",
     "responseheaders",
     "error",
-
+    # WebSocket
     "websocket_handshake",
     "websocket_start",
     "websocket_message",
     "websocket_error",
     "websocket_end",
-
+    # misc
     "next_layer",
-
     "configure",
     "done",
     "log",
@@ -38,38 +40,57 @@ Events = frozenset([
     "update",
 ])
 
+TEventGenerator = typing.Iterator[typing.Tuple[str, typing.Any]]
 
-def iterate(f):
-    if isinstance(f, http.HTTPFlow):
-        if f.request:
-            yield "requestheaders", f
-            yield "request", f
-        if f.response:
-            yield "responseheaders", f
-            yield "response", f
-        if f.error:
-            yield "error", f
-    elif isinstance(f, websocket.WebSocketFlow):
-        messages = f.messages
-        f.messages = []
-        f.reply = controller.DummyReply()
-        yield "websocket_start", f
-        while messages:
-            f.messages.append(messages.pop(0))
-            yield "websocket_message", f
-        if f.error:
-            yield "websocket_error", f
-        yield "websocket_end", f
-    elif isinstance(f, tcp.TCPFlow):
-        messages = f.messages
-        f.messages = []
-        f.reply = controller.DummyReply()
-        yield "tcp_start", f
-        while messages:
-            f.messages.append(messages.pop(0))
-            yield "tcp_message", f
-        if f.error:
-            yield "tcp_error", f
-        yield "tcp_end", f
+
+def _iterate_http(f: http.HTTPFlow) -> TEventGenerator:
+    if f.request:
+        yield "requestheaders", f
+        yield "request", f
+    if f.response:
+        yield "responseheaders", f
+        yield "response", f
+    if f.error:
+        yield "error", f
+
+
+def _iterate_websocket(f: websocket.WebSocketFlow) -> TEventGenerator:
+    messages = f.messages
+    f.messages = []
+    f.reply = controller.DummyReply()
+    yield "websocket_start", f
+    while messages:
+        f.messages.append(messages.pop(0))
+        yield "websocket_message", f
+    if f.error:
+        yield "websocket_error", f
+    yield "websocket_end", f
+
+
+def _iterate_tcp(f: tcp.TCPFlow) -> TEventGenerator:
+    messages = f.messages
+    f.messages = []
+    f.reply = controller.DummyReply()
+    yield "tcp_start", f
+    while messages:
+        f.messages.append(messages.pop(0))
+        yield "tcp_message", f
+    if f.error:
+        yield "tcp_error", f
+    yield "tcp_end", f
+
+
+_iterate_map = {
+    http.HTTPFlow: _iterate_http,
+    websocket.WebSocketFlow: _iterate_websocket,
+    tcp.TCPFlow: _iterate_tcp,
+}  # type: typing.Dict[typing.Type[flow.Flow], typing.Callable[[typing.Any], TEventGenerator]]
+
+
+def iterate(f: flow.Flow) -> TEventGenerator:
+    try:
+        e = _iterate_map[type(f)]
+    except KeyError as err:
+        raise TypeError("Unknown flow type: {}".format(f)) from err
     else:
-        raise TypeError()
+        yield from e(f)
diff --git a/mitmproxy/options.py b/mitmproxy/options.py
index e6c2fed67..954db7e8c 100644
--- a/mitmproxy/options.py
+++ b/mitmproxy/options.py
@@ -209,15 +209,11 @@ class Options(optmanager.OptManager):
         self.add_option(
             "proxyauth", Optional[str], None,
             """
-            Require proxy authentication. Value may be "any" to require
-            authenticaiton but accept any credentials, start with "@" to specify
-            a path to an Apache htpasswd file, be of the form
-            "username:password", or be of the form
-            "ldap[s]:url_server_ldap:dn_auth:password:dn_subtree",
-            the dn_auth & password is the dn/pass used to authenticate
-            the dn subtree is the subtree that we will search to find the username
-            an example would be
-            "ldap:localhost:cn=default,dc=example,dc=com:password:ou=application,dc=example,dc=com".
+            Require proxy authentication. Format:
+            "username:pass",
+            "any" to accept any user/pass combination,
+            "@path" to use an Apache htpasswd file,
+            or "ldap[s]:url_server_ldap:dn_auth:password:dn_subtree" for LDAP authentication.
             """
         )
         self.add_option(
@@ -288,7 +284,7 @@ class Options(optmanager.OptManager):
             """
             Mode can be "regular", "transparent", "socks5", "reverse:SPEC",
             or "upstream:SPEC". For reverse and upstream proxy modes, SPEC
-            is proxy specification in the form of "http[s]://host[:port]".
+            is host specification in the form of "http[s]://host[:port]".
             """
         )
         self.add_option(
@@ -311,9 +307,8 @@ class Options(optmanager.OptManager):
         self.add_option(
             "http2_priority", bool, False,
             """
-            PRIORITY forwarding for HTTP/2 connections. PRIORITY forwarding is
-            disabled by default, because some webservers fail to implement the
-            RFC properly.
+            PRIORITY forwarding for HTTP/2 connections. Disabled by default to ensure compatibility
+            with misbehaving servers.
             """
         )
         self.add_option(
@@ -337,7 +332,7 @@ class Options(optmanager.OptManager):
         self.add_option(
             "upstream_auth", Optional[str], None,
             """
-            Add HTTP Basic authentcation to upstream proxy and reverse proxy
+            Add HTTP Basic authentication to upstream proxy and reverse proxy
             requests. Format: username:password.
             """
         )
diff --git a/mitmproxy/tools/cmdline.py b/mitmproxy/tools/cmdline.py
index 97b04e743..68ddc2c8e 100644
--- a/mitmproxy/tools/cmdline.py
+++ b/mitmproxy/tools/cmdline.py
@@ -2,7 +2,6 @@ import argparse
 import os
 
 from mitmproxy import options
-from mitmproxy import version
 
 
 CONFIG_PATH = os.path.join(options.CA_DIR, "config.yaml")
@@ -12,14 +11,9 @@ def common_options(parser, opts):
     parser.add_argument(
         '--version',
         action='store_true',
+        help="show version number and exit",
         dest='version',
     )
-    parser.add_argument(
-        '--shortversion',
-        action='version',
-        help="show program's short version number and exit",
-        version=version.VERSION
-    )
     parser.add_argument(
         '--options',
         action='store_true',
diff --git a/mitmproxy/utils/human.py b/mitmproxy/utils/human.py
index b3934846c..d67fb3104 100644
--- a/mitmproxy/utils/human.py
+++ b/mitmproxy/utils/human.py
@@ -71,7 +71,7 @@ def format_address(address: tuple) -> str:
     """
     try:
         host = ipaddress.ip_address(address[0])
-        if host.version == 4:
+        if isinstance(host, ipaddress.IPv4Address):
             return "{}:{}".format(str(host), address[1])
         # If IPv6 is mapped to IPv4
         elif host.ipv4_mapped:
diff --git a/setup.py b/setup.py
index 212ad95ea..441a1d8f9 100644
--- a/setup.py
+++ b/setup.py
@@ -90,7 +90,7 @@ setup(
         'dev': [
             "flake8>=3.2.1, <3.4",
             "Flask>=0.10.1, <0.13",
-            "mypy>=0.501, <0.512",
+            "mypy>=0.501, <0.521",
             "pytest-cov>=2.2.1, <3",
             "pytest-faulthandler>=1.3.0, <2",
             "pytest-timeout>=1.0.0, <2",