diff --git a/pymysqlreplication/gtid.py b/pymysqlreplication/gtid.py
index c2a30145..e0f7c1dc 100644
--- a/pymysqlreplication/gtid.py
+++ b/pymysqlreplication/gtid.py
@@ -1,14 +1,16 @@
 # -*- coding: utf-8 -*-
+from __future__ import annotations
+from typing import List, Tuple, Union, Set, Optional
 
 import re
 import struct
 import binascii
 from io import BytesIO
 
-def overlap(i1, i2):
+def overlap(i1: Tuple[int, int], i2: Tuple[int, int]) -> bool:
     return i1[0] < i2[1] and i1[1] > i2[0]
 
-def contains(i1, i2):
+def contains(i1: Tuple[int, int], i2: Tuple[int, int]) -> bool:
     return i2[0] >= i1[0] and i2[1] <= i1[1]
 
 class Gtid(object):
@@ -47,8 +49,19 @@ class Gtid(object):
         Exception: Adding an already present transaction number (one that overlaps).
         Exception: Adding a Gtid with a different SID.
     """
+    def __init__(self, gtid: str, sid=None, intervals: List[Tuple[int, int]]=[]):
+        if sid:
+            intervals = intervals
+        else:
+            sid, intervals = Gtid.parse(gtid)
+
+        self.sid: str = sid
+        self.intervals: List[Tuple[int, int]] = []
+        for itvl in intervals:
+            self.__add_interval(itvl)
+
     @staticmethod
-    def parse_interval(interval):
+    def parse_interval(interval: str) -> Tuple[int, int]:
         """
         We parse a human-generated string here. So our end value b
         is incremented to conform to the internal representation format.
@@ -64,7 +77,7 @@ def parse_interval(interval):
         return (a, b+1)
 
     @staticmethod
-    def parse(gtid):
+    def parse(gtid: str) -> Tuple[str, List[Tuple[int, int]]]:
         """Parse a GTID from mysql textual format.
 
         Raises:
@@ -83,7 +96,7 @@ def parse(gtid):
 
         return (sid, intervals_parsed)
 
-    def __add_interval(self, itvl):
+    def __add_interval(self, itvl: Tuple[int, int]):
         """
         Use the internal representation format and add it
         to our intervals, merging if required.
@@ -113,7 +126,7 @@ def __add_interval(self, itvl):
 
         self.intervals = sorted(new + [itvl])
 
-    def __sub_interval(self, itvl):
+    def __sub_interval(self, itvl: Tuple[int, int]):
         """Using the internal representation, remove an interval
 
         Raises: Exception if itvl malformated"""
@@ -138,25 +151,16 @@ def __sub_interval(self, itvl):
 
         self.intervals = new
 
-    def __contains__(self, other):
+    def __contains__(self, other: Gtid) -> bool:
         if other.sid != self.sid:
             return False
 
         return all(any(contains(me, them) for me in self.intervals)
                    for them in other.intervals)
 
-    def __init__(self, gtid, sid=None, intervals=[]):
-        if sid:
-            intervals = intervals
-        else:
-            sid, intervals = Gtid.parse(gtid)
 
-        self.sid = sid
-        self.intervals = []
-        for itvl in intervals:
-            self.__add_interval(itvl)
 
-    def __add__(self, other):
+    def __add__(self, other: Gtid) -> Gtid:
         """Include the transactions of this gtid.
 
         Raises:
@@ -172,7 +176,7 @@ def __add__(self, other):
 
         return result
 
-    def __sub__(self, other):
+    def __sub__(self, other: Gtid) -> Gtid:
         """Remove intervals. Do not raise, if different SID simply
         ignore"""
         result = Gtid(str(self))
@@ -184,7 +188,7 @@ def __sub__(self, other):
 
         return result
 
-    def __str__(self):
+    def __str__(self) -> str:
         """We represent the human value here - a single number
         for one transaction, or a closed interval (decrementing b)"""
         return '%s:%s' % (self.sid,
@@ -192,18 +196,18 @@ def __str__(self):
                                    else str(x[0])
                                    for x in self.intervals))
 
-    def __repr__(self):
+    def __repr__(self) -> str:
         return '<Gtid "%s">' % self
 
     @property
-    def encoded_length(self):
+    def encoded_length(self) -> int:
         return (16 +  # sid
                 8 +  # n_intervals
                 2 *  # stop/start
                 8 *  # stop/start mark encoded as int64
                 len(self.intervals))
 
-    def encode(self):
+    def encode(self) -> bytes:
         buffer = b''
         # sid
         buffer += binascii.unhexlify(self.sid.replace('-', ''))
@@ -219,7 +223,7 @@ def encode(self):
         return buffer
 
     @classmethod
-    def decode(cls, payload):
+    def decode(cls, payload: BytesIO) -> Gtid:
         assert isinstance(payload, BytesIO), \
             'payload is expected to be a BytesIO'
         sid = b''
@@ -236,13 +240,11 @@ def decode(cls, payload):
         (n_intervals,) = struct.unpack('<Q', payload.read(8))
         intervals = []
         for i in range(0, n_intervals):
-            start, end = struct.unpack('<QQ', payload.read(16))
+            (start, end) = struct.unpack('<QQ', payload.read(16))
             intervals.append((start, end-1))
 
         return cls('%s:%s' % (sid.decode('ascii'), ':'.join([
             '%d-%d' % x
-            if isinstance(x, tuple)
-            else '%d' % x
             for x in intervals])))
 
     def __cmp__(self, other):
@@ -250,27 +252,38 @@ def __cmp__(self, other):
             return cmp(self.sid, other.sid)
         return cmp(self.intervals, other.intervals)
 
-    def __eq__(self, other):
+    def __eq__(self, other: object) -> bool:
+        """Equality between a Gtid and an other Gtid.
+
+        Raise: NotImplemented if compared with anything else.
+        """
+        if not isinstance(other, Gtid):
+            raise NotImplemented
+
         if other.sid != self.sid:
             return False
         return self.intervals == other.intervals
 
-    def __lt__(self, other):
+    def __lt__(self, other: Gtid) -> bool:
+        """Check if a Gtid is lesser an other Gtid.
+        """
         if other.sid != self.sid:
             return self.sid < other.sid
         return self.intervals < other.intervals
 
-    def __le__(self, other):
+    def __le__(self, other: Gtid) -> bool:
+        """Check if a Gtid is lesser or equal an other Gtid.
+        """
         if other.sid != self.sid:
             return self.sid <= other.sid
         return self.intervals <= other.intervals
 
-    def __gt__(self, other):
+    def __gt__(self, other: Gtid) -> bool:
         if other.sid != self.sid:
             return self.sid > other.sid
         return self.intervals > other.intervals
 
-    def __ge__(self, other):
+    def __ge__(self, other: Gtid) -> bool:
         if other.sid != self.sid:
             return self.sid >= other.sid
         return self.intervals >= other.intervals
@@ -278,7 +291,7 @@ def __ge__(self, other):
 
 class GtidSet(object):
     """Represents a set of Gtid"""
-    def __init__(self, gtid_set):
+    def __init__(self, gtid_set: Optional[Union[str, Union[Set[Gtid], Set[str], List[Gtid], List[str]]]]):
         """
         Construct a GtidSet initial state depends of the nature of `gtid_set` param.
 
@@ -300,7 +313,7 @@ def _to_gtid(element):
             return Gtid(element.strip(' \n'))
 
         if not gtid_set:
-            self.gtids = []
+            self.gtids: List[Gtid] = []
         elif isinstance(gtid_set, (list, set)):
             self.gtids = [_to_gtid(x) for x in gtid_set]
         else:
@@ -317,7 +330,7 @@ def merge_gtid(self, gtid):
             new_gtids.append(gtid)
         self.gtids = new_gtids
 
-    def __contains__(self, other):
+    def __contains__(self, other: Union[GtidSet, Gtid]) -> bool:
         """
         Raises:
            - NotImplementedError other is not a GtidSet neither a Gtid,
@@ -329,7 +342,7 @@ def __contains__(self, other):
             return any(other in x for x in self.gtids)
         raise NotImplementedError
 
-    def __add__(self, other):
+    def __add__(self, other: Union[GtidSet, Gtid]) -> GtidSet:
         """
         Merge current instance with an other GtidSet or with a Gtid alone.
 
@@ -350,33 +363,39 @@ def __add__(self, other):
 
         raise NotImplementedError
 
-    def __str__(self):
+    def __str__(self) -> str:
         """
         Returns a comma separated string of gtids.
         """
         return ','.join(str(x) for x in self.gtids)
 
-    def __repr__(self):
+    def __repr__(self) -> str:
         return '<GtidSet %r>' % self.gtids
 
     @property
-    def encoded_length(self):
+    def encoded_length(self) -> int:
         return (8 +  # n_sids
                 sum(x.encoded_length for x in self.gtids))
 
-    def encoded(self):
+    def encoded(self) -> bytes:
         return b'' + (struct.pack('<Q', len(self.gtids)) +
                       b''.join(x.encode() for x in self.gtids))
 
     encode = encoded
 
     @classmethod
-    def decode(cls, payload):
+    def decode(cls, payload: BytesIO) -> GtidSet:
         assert isinstance(payload, BytesIO), \
             'payload is expected to be a BytesIO'
         (n_sid,) = struct.unpack('<Q', payload.read(8))
 
         return cls([Gtid.decode(payload) for _ in range(0, n_sid)])
 
-    def __eq__(self, other):
+    def __eq__(self, other: object) -> bool:
+        """Equality between a GtidSet and an other GtidSet.
+
+        Raise: NotImplemented if compared with anything else.
+        """
+        if not isinstance(other, GtidSet):
+            raise NotImplemented
         return self.gtids == other.gtids