diff --git a/src/contracts/__init__.py b/src/contracts/__init__.py
index eea09362..813e7a76 100644
--- a/src/contracts/__init__.py
+++ b/src/contracts/__init__.py
@@ -1,4 +1,4 @@
-__version__ = '1.8.12'
+__version__ = '1.8.13'
 
 import logging
 
diff --git a/src/contracts/interface.py b/src/contracts/interface.py
index 2d28f787..276651e4 100644
--- a/src/contracts/interface.py
+++ b/src/contracts/interface.py
@@ -12,10 +12,10 @@ class Where(object):
 
         All parsed elements contain a reference to a :py:class:`Where` object
         so that we can output pretty error messages.
-        
-        
+
+
         Character should be >= len(string) (possibly outside the string).
-        Character_end should be >= character (so that you can splice with 
+        Character_end should be >= character (so that you can splice with
         string[character:character_end])
     """
 
@@ -38,7 +38,7 @@ def __init__(self, string, character, character_end=None):
             #                                             or (character <= character_end - 1)):
             #             character += 1
             #         else:
-            #             break  
+            #             break
         self.line, self.col = line_and_col(character, string)
 
         if character_end is not None:
@@ -93,7 +93,7 @@ def __str__(self):
 # mark = 'here or nearby'
 def format_where(w, context_before=3, mark=None, arrow=True,
                  use_unicode=True, no_mark_arrow_if_longer_than=3):
-    s = u''
+    s = ''
     if w.filename:
         s += 'In file %r:\n' % w.filename
     lines = w.string.split('\n')
@@ -108,7 +108,7 @@ def format_where(w, context_before=3, mark=None, arrow=True,
     for i in range(start, w.line + 1):
         # suppress empty lines
         if one_written or lines[i].strip():
-            s += (u"%s%s\n" % (pattern % (i + 1), lines[i]))
+            s += ("%s%s\n".format(pattern % (i + 1), lines[i],))
             one_written = True
 
     fill = len(pattern % maxi)
@@ -119,29 +119,29 @@ def format_where(w, context_before=3, mark=None, arrow=True,
     space_before = Where(w.string, char0, char0_end)
 
     nindent = printable_length_where(space_before)
-    space = u' ' * fill + u' ' * nindent
+    space = ' ' * fill + ' ' * nindent
     if w.col_end is not None:
         if w.line == w.line_end:
             num_highlight = printable_length_where(w)
-            s += space + u'~' * num_highlight + '\n'
-            space += u' ' * (num_highlight / 2)
+            s += space + '~' * num_highlight + '\n'
+            space += ' ' * (num_highlight / 2)
         else:
             # cannot highlight if on different lines
             num_highlight = None
             pass
     else:
         num_highlight = None
-    # Do not add the arrow and the mark if we have a long underline string 
+    # Do not add the arrow and the mark if we have a long underline string
 
     disable_mark_arrow = (num_highlight is not None) and (no_mark_arrow_if_longer_than < num_highlight)
 
     if not disable_mark_arrow:
         if arrow:
             if use_unicode:
-                s += space + u'↑\n'
+                s += space + '↑\n'
             else:
-                s += space + u'^\n'
-                s += space + u'|\n'
+                s += space + '^\n'
+                s += space + '|\n'
 
         if mark is not None:
             s += space + mark
@@ -173,7 +173,7 @@ def line_and_col(loc, strg):
     from .utils import check_isinstance
     check_isinstance(loc, int)
     check_isinstance(strg, six.string_types)
-    # first find the line 
+    # first find the line
     lines = strg.split('\n')
 
     if loc == len(strg):
@@ -433,8 +433,8 @@ def check_contract(self, context, value, silent):  # @UnusedVariable
             context. This is the function that subclasses must implement.
 
             If silent = False, do not bother with creating detailed error messages yet.
-            This is for performance optimization. 
-            
+            This is for performance optimization.
+
             :param context: The context in which expressions are evaluated.
             :type context:
         """
@@ -548,7 +548,6 @@ def clipped_repr(x, clip):
         s = "%s%s" % (s[:cut], clip_tag)
     return s
 
-
 # TODO: add checks for these functions
 
 
@@ -620,7 +619,7 @@ def describe_value_multiline(x):
             try:
                 # This fails for classes
                 final = "{}\n{}".format(desc, x.__repr__())
-            except: # XXX
+            except:  # XXX
                 final = "%s\n%s" % (desc, x)
 
             return final
diff --git a/src/contracts/library/map.py b/src/contracts/library/map.py
index bae047dc..d045dda7 100644
--- a/src/contracts/library/map.py
+++ b/src/contracts/library/map.py
@@ -1,7 +1,11 @@
 from ..interface import Contract, ContractNotRespected
 from ..syntax import (W, contract_expression, O, S, add_contract, add_keyword,
     Keyword)
-import collections
+
+try:
+    import collections.abc as collectionsAbc  # python 3.6+
+except ImportError:
+    import collections as collectionsAbc
 
 
 class Map(Contract):
@@ -13,7 +17,7 @@ def __init__(self, length=None, key_c=None, value_c=None, where=None):
         self.value_c = value_c
 
     def check_contract(self, context, value, silent):
-        if not isinstance(value, collections.Mapping):
+        if not isinstance(value, collectionsAbc.Mapping):
             error = 'Expected a Mapping, got %r.' % value.__class__.__name__
             raise ContractNotRespected(contract=self, error=error,
                                        value=value, context=context)
@@ -57,7 +61,7 @@ def parse_action(s, loc, tokens):
 
 length_spec = S('[') - contract_expression('length') - S(']')
 kv_spec = ('(' - O(contract_expression('key')) + ':'
-           + O(contract_expression('value')) - ')')
+           +O(contract_expression('value')) - ')')
 dict_contract = Keyword('map') + O(length_spec) + O(kv_spec)
 
 dict_contract.setParseAction(Map.parse_action)
diff --git a/src/contracts/library/miscellaneous_aliases.py b/src/contracts/library/miscellaneous_aliases.py
index 8d9844da..1717c5c2 100644
--- a/src/contracts/library/miscellaneous_aliases.py
+++ b/src/contracts/library/miscellaneous_aliases.py
@@ -1,12 +1,16 @@
-import collections
-
+try:
+    import collections.abc as collectionsAbc  # python 3.6+
+except ImportError:
+    import collections as collectionsAbc
 
 
 def ist(C):
+
     def f(x):
         f.__name__ = 'isinstance_of_%s' % C.__name__
         if not isinstance(x, C):
             raise ValueError('Value is not an instance of %s.' % C.__name__)
+
     return f
 
 
@@ -14,33 +18,32 @@ def m_new_contract(name, f):
     from contracts.library.extensions import CheckCallable
     from contracts.library.extensions import Extension
     Extension.registrar[name] = CheckCallable(f)
-    
 
-m_new_contract('Container', ist(collections.Container))
-# todo: Iterable(x)
-m_new_contract('Iterable', ist(collections.Iterable))
-
-m_new_contract('Hashable', ist(collections.Hashable))
 
+m_new_contract('Container', ist(collectionsAbc.Container))
+# todo: Iterable(x)
+m_new_contract('Iterable', ist(collectionsAbc.Iterable))
 
+m_new_contract('Hashable', ist(collectionsAbc.Hashable))
 
-m_new_contract('Iterator', ist(collections.Iterator))
-m_new_contract('Sized', ist(collections.Sized))
-m_new_contract('Callable', ist(collections.Callable))
-m_new_contract('Sequence', ist(collections.Sequence))
-m_new_contract('Set', ist(collections.Set))
-m_new_contract('MutableSequence', ist(collections.MutableSequence))
-m_new_contract('MutableSet', ist(collections.MutableSet))
-m_new_contract('Mapping', ist(collections.Mapping))
-m_new_contract('MutableMapping', ist(collections.MutableMapping))
-#new_contract('MappingView', ist(collections.MappingView))
-#new_contract('ItemsView', ist(collections.ItemsView))
-#new_contract('ValuesView', ist(collections.ValuesView))
+m_new_contract('Iterator', ist(collectionsAbc.Iterator))
+m_new_contract('Sized', ist(collectionsAbc.Sized))
+m_new_contract('Callable', ist(collectionsAbc.Callable))
+m_new_contract('Sequence', ist(collectionsAbc.Sequence))
+m_new_contract('Set', ist(collectionsAbc.Set))
+m_new_contract('MutableSequence', ist(collectionsAbc.MutableSequence))
+m_new_contract('MutableSet', ist(collectionsAbc.MutableSet))
+m_new_contract('Mapping', ist(collectionsAbc.Mapping))
+m_new_contract('MutableMapping', ist(collectionsAbc.MutableMapping))
+# new_contract('MappingView', ist(collections.MappingView))
+# new_contract('ItemsView', ist(collections.ItemsView))
+# new_contract('ValuesView', ist(collections.ValuesView))
 
 
 # Not a lambda to have better messages
-def is_None(x): 
+def is_None(x):
     return x is None
 
+
 m_new_contract('None', is_None)
 m_new_contract('NoneType', is_None)
diff --git a/src/contracts/library/seq.py b/src/contracts/library/seq.py
index 9d8586e7..5e46cdc6 100644
--- a/src/contracts/library/seq.py
+++ b/src/contracts/library/seq.py
@@ -1,7 +1,12 @@
 from ..interface import Contract, ContractNotRespected
 from ..syntax import (add_contract, W, contract_expression, O, S, add_keyword,
     Keyword)
-import collections
+
+try:
+    import collections.abc as collectionsAbc  # python 3.6+
+except ImportError:
+    import collections as collectionsAbc
+
 from past.builtins import xrange
 
 try:
@@ -38,7 +43,7 @@ def check_contract(self, context, value, silent):
 
             return
 
-        if not isinstance(value, collections.Sequence):
+        if not isinstance(value, collectionsAbc.Sequence):
             error = 'Expected a Sequence, got %r.' % value.__class__.__name__
             raise ContractNotRespected(self, error, value, context)
 
diff --git a/src/contracts/library/sets.py b/src/contracts/library/sets.py
index dc37279c..26d9d0f4 100644
--- a/src/contracts/library/sets.py
+++ b/src/contracts/library/sets.py
@@ -1,7 +1,10 @@
 from ..interface import Contract, ContractNotRespected, describe_type
 from ..syntax import (Keyword, O, S, W, add_contract, add_keyword,
     contract_expression)
-import collections
+try:
+    import collections.abc as collectionsAbc  # python 3.6+
+except ImportError:
+    import collections as collectionsAbc
 
 
 class ASet(Contract):
@@ -13,7 +16,7 @@ def __init__(self, length_contract=None,
         self.elements_contract = elements_contract
 
     def check_contract(self, context, value, silent):
-        if not isinstance(value, collections.Set):
+        if not isinstance(value, collectionsAbc.Set):
             error = 'Expected a set, got %r.' % describe_type(value)
             raise ContractNotRespected(self, error, value, context)
 
diff --git a/src/contracts/main.py b/src/contracts/main.py
index 7722cb3e..70d07023 100644
--- a/src/contracts/main.py
+++ b/src/contracts/main.py
@@ -146,10 +146,10 @@ def tmp_wrap(f):  # do not change name (see above)
                 try:
                     return contracts_decorate(f, **kwargs)
                 except ContractSyntaxError as e:
-                    msg = u"Cannot decorate function %s:" % f.__name__
+                    msg = "Cannot decorate function %s:".format(f.__name__)
                     from .utils import indent
                     import traceback
-                    msg += u'\n\n' + indent(traceback.format_exc(), u'  ')
+                    msg += '\n\n' + indent(traceback.format_exc(), '  ')
                     raise ContractSyntaxError(msg, e.where)
                     # erase the stack
                 except ContractDefinitionError as e:
@@ -596,7 +596,7 @@ def new_contract_impl(identifier, condition):
         loc = e.loc
         if loc >= len(identifier):
             loc -= 1
-        where = Where(identifier, character=loc)  #line=e.lineno, column=e.col)
+        where = Where(identifier, character=loc)  # line=e.lineno, column=e.col)
         # msg = 'Error in parsing string: %s' % e
         msg = ('The given identifier %r does not correspond to my idea '
                'of what an identifier should look like;\n%s\n%s'
@@ -659,7 +659,7 @@ def new_contract_impl(identifier, condition):
             assert c == expected, \
                 'Expected %r, got %r.' % (c, expected)  # pragma: no cover
         except ContractSyntaxError:  # pragma: no cover
-            #assert False, 'Cannot parse %r: %s' % (identifier, e)
+            # assert False, 'Cannot parse %r: %s' % (identifier, e)
             raise
 
     return contract
diff --git a/src/contracts/testing/test_unicode_literals.py b/src/contracts/testing/test_unicode_literals.py
index 30b21862..a0896e43 100644
--- a/src/contracts/testing/test_unicode_literals.py
+++ b/src/contracts/testing/test_unicode_literals.py
@@ -7,10 +7,11 @@
 
 import unittest
 
+
 class TestParsingNumbers(unittest.TestCase):
 
     def test_unicode_literal(self):
-        r = parse_contract_string(u'int')
+        r = parse_contract_string('int')
         print(r)
 
     def test_unicode_literal2(self):
@@ -19,5 +20,4 @@ def test_unicode_literal2(self):
         def f(x):
             pass
 
-
         f('')
diff --git a/src/contracts/utils.py b/src/contracts/utils.py
index df1ffa1f..22b7157b 100644
--- a/src/contracts/utils.py
+++ b/src/contracts/utils.py
@@ -19,17 +19,17 @@
 
 def indent(s, prefix, first=None):
     if not isinstance(s, six.string_types):
-        s = u'{}'.format(s)
+        s = '{}'.format(s)
 
     assert isinstance(prefix, six.string_types)
     try:
         lines = s.split('\n')
     except UnicodeDecodeError:
-        print(type(s)) # XXX
-        print(s) # XXX
+        print(type(s))  # XXX
+        print(s)  # XXX
         lines = [s]
     if not lines:
-        return u''
+        return ''
 
     if first is None:
         first = prefix
@@ -40,8 +40,8 @@ def indent(s, prefix, first=None):
     first = ' ' * (m - len(first)) + first
 
     # differnet first prefix
-    res = [u'%s%s' % (prefix, line.rstrip()) for line in lines]
-    res[0] = u'%s%s' % (first, lines[0].rstrip())
+    res = ['%s%s'.format(prefix, line.rstrip()) for line in lines]
+    res[0] = '%s%s'.format(first, lines[0].rstrip())
     return '\n'.join(res)
 
 
@@ -117,7 +117,7 @@ def _get_str(x, informal):
 
 def format_list_long(l, informal=False):
     """
-        - My 
+        - My
           first
         - Second
     """
@@ -163,9 +163,9 @@ def raise_wrapped(etype, e, msg, compact=False, **kwargs):
     """ Raises an exception of type etype by wrapping
         another exception "e" with its backtrace and adding
         the objects in kwargs as formatted by format_obs.
-        
+
         if compact = False, write the whole traceback, otherwise just str(e).
-    
+
         exc = output of sys.exc_info()
     """
 
@@ -202,6 +202,7 @@ def raise_wrapped_make(etype, e, msg, compact=False, **kwargs):
 
     return etype(s)
 
+
 def _format_exc(msg, **kwargs):
     check_isinstance(msg, six.text_type)
     s = msg
@@ -212,7 +213,7 @@ def _format_exc(msg, **kwargs):
 
 def raise_desc(etype, msg, args_first=False, **kwargs):
     """
-    
+
         Example:
             raise_desc(ValueError, "I don't know", a=a, b=b)
     """
@@ -230,7 +231,6 @@ def raise_desc(etype, msg, args_first=False, **kwargs):
 
     raise etype(s)
 
-
 #
 #
 #
@@ -269,9 +269,9 @@ def raise_desc(etype, msg, args_first=False, **kwargs):
 #         n = n+1
 #     return list
 
-
 # from decorator import decorator  # @UnresolvedImport
 
+
 def ignore_typeerror(f):
     """ Recasts TypeError as Exception; otherwise pyparsing gets confused. """