diff --git a/docs/conf.py b/docs/conf.py
index 5bf4a1d..3a96e45 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -31,7 +31,7 @@ def get_version(version_file):
     requirements list of this package (otherwise it cannot be executed in
     a fresh Python environment).
     """
-    with open(version_file, 'r') as fp:
+    with open(version_file) as fp:
         version_source = fp.read()
     globals = {}
     exec(version_source, globals)
@@ -97,12 +97,12 @@ def get_version(version_file):
 os.environ['BUILDING_DOCS'] = '1'
 
 # General information about the project.
-project = u'nocasedict'
+project = 'nocasedict'
 #copyright = u''
-author = u"Andreas Maier"
+author = "Andreas Maier"
 
 # The short description of the package.
-_short_description = u"A case-insensitive ordered dictionary for Python"
+_short_description = "A case-insensitive ordered dictionary for Python"
 
 # The version info for the project you're documenting, acts as replacement for
 # |version| and |release|, also used in various other places throughout the
@@ -582,7 +582,7 @@ def __init__(self, *args, **kwargs):
         self._logger = logging.getLogger(__name__)  # requires Sphinx 1.6.1
         self._log_prefix = "conf.py/AutoAutoSummary"
         self._excluded_classes = ['BaseException']
-        super(AutoAutoSummary, self).__init__(*args, **kwargs)
+        super().__init__(*args, **kwargs)
 
     def _get_members(self, class_obj, member_type, include_in_public=None):
         """
@@ -690,7 +690,7 @@ def run(self):
                 self._log_prefix, exc.__class__.__name__, exc)
 
         finally:
-            return super(AutoAutoSummary, self).run()
+            return super().run()
 
 
 def setup(app):
diff --git a/nocasedict/__init__.py b/nocasedict/__init__.py
index 0d9f436..c0ff654 100644
--- a/nocasedict/__init__.py
+++ b/nocasedict/__init__.py
@@ -2,7 +2,6 @@
 nocasedict - A case-insensitive ordered dictionary for Python
 """
 
-from __future__ import absolute_import
 
 from ._version import __version__  # noqa: F401
 from ._nocasedict import *  # noqa: F403,F401
diff --git a/nocasedict/_hashable.py b/nocasedict/_hashable.py
index 98bcf4a..b2677b0 100644
--- a/nocasedict/_hashable.py
+++ b/nocasedict/_hashable.py
@@ -2,7 +2,6 @@
 This module provides class HashableMixin.
 """
 
-from __future__ import print_function, absolute_import
 
 from typing import Any
 from ._nocasedict import NocaseDict
diff --git a/nocasedict/_keyableby.py b/nocasedict/_keyableby.py
index 14567a0..6d5c65a 100644
--- a/nocasedict/_keyableby.py
+++ b/nocasedict/_keyableby.py
@@ -3,7 +3,6 @@
 class NocaseDict.
 """
 
-from __future__ import print_function, absolute_import
 
 from typing import Type
 
diff --git a/nocasedict/_nocasedict.py b/nocasedict/_nocasedict.py
index f2c7a55..7663cc3 100644
--- a/nocasedict/_nocasedict.py
+++ b/nocasedict/_nocasedict.py
@@ -30,27 +30,16 @@
 The only class exposed by this package is :class:`nocasedict.NocaseDict`.
 """
 
-from __future__ import print_function, absolute_import
 
-import sys
 import os
-import warnings
-from collections import OrderedDict
 from collections.abc import MutableMapping, KeysView, ValuesView, ItemsView
 from typing import Any, AnyStr, NoReturn, Optional, Iterator, Tuple, Dict
 
-from ._utils import _stacklevel_above_nocasedict
-
 __all__ = ['NocaseDict']
 
-# Starting with Python 3.7, the standard dict is guaranteed to be ordered.
-# Note: In CPython, that already happened in 3.6, but it was not guaranteed
-# for all implementations.
-# pylint: disable=invalid-name
-if sys.version_info[0:2] >= (3, 7):
-    _ODICT_TYPE = dict
-else:
-    _ODICT_TYPE = OrderedDict
+# Note: Since the minimum version for nocasedict is Python 3.8, the standard
+# dict is guaranteed to be ordered and the implementation uses dict when an
+# ordered dict is needed.
 
 Key = Optional[AnyStr]
 
@@ -77,6 +66,7 @@ def __len__(self):
         return len(self._dict)
 
     def __contains__(self, x):
+        # pylint: disable=invalid-name
         return x in iter(self)
 
     def __reversed__(self):
@@ -87,7 +77,7 @@ def __repr__(self):
 
 
 class dict_keys(_DictView, KeysView):
-    # pylint: disable=too-few-public-methods
+    # pylint: disable=too-few-public-methods,invalid-name
     """
     Dictionary values view.
     """
@@ -100,7 +90,7 @@ def __iter__(self):
 
 
 class dict_values(_DictView, ValuesView):
-    # pylint: disable=too-few-public-methods
+    # pylint: disable=too-few-public-methods,invalid-name
     """
     Dictionary values view.
     """
@@ -113,7 +103,7 @@ def __iter__(self):
 
 
 class dict_items(_DictView, ItemsView):
-    # pylint: disable=too-few-public-methods
+    # pylint: disable=too-few-public-methods,invalid-name
     """
     Dictionary items view.
     """
@@ -263,7 +253,7 @@ def __init__(self, *args, **kwargs) -> None:
 
         # The internal dictionary, with casefolded keys. An item in this dict
         # is the tuple (original key, value).
-        self._data: Dict[Key, Any] = _ODICT_TYPE()
+        self._data: Dict[Key, Any] = {}
 
         self.update(*args, **kwargs)
 
@@ -597,23 +587,12 @@ def update(self, *args, **kwargs) -> None:
         if args:
             if len(args) > 1:
                 raise TypeError(
-                    "Expected at most 1 positional argument, got {n}".
-                    format(n=len(args)))
+                    f"Expected at most 1 positional argument, got {len(args)}")
             other = args[0]
             try:
                 # Try mapping / dictionary
                 for key in other.keys():
                     self[key] = other[key]
-                # pylint: disable=unidiomatic-typecheck
-                if type(other) is dict and _ODICT_TYPE is not dict and \
-                        len(other.keys()) > 1:
-                    warnings.warn(
-                        "Before Python 3.7, initializing or updating a "
-                        "NocaseDict object from a dict object with more than "
-                        "one item is not guaranteed to preserve the order of "
-                        "its items",
-                        UserWarning,
-                        stacklevel=_stacklevel_above_nocasedict())
             except AttributeError:
                 # Expecting an iterable
 
@@ -632,9 +611,8 @@ def update(self, *args, **kwargs) -> None:
                             key, value = item
                         except ValueError as exc:
                             value_error = ValueError(
-                                "Cannot unpack positional argument item #{i} "
-                                "of type {t} into key, value: {exc}".
-                                format(i=i, t=type(item), exc=exc))
+                                f"Cannot unpack positional argument item #{i} "
+                                f"of type {type(item)} into key, value: {exc}")
                             value_error.__cause__ = None  # Suppress 'During..'
                             # pylint: disable=raise-missing-from
                             raise value_error
@@ -642,13 +620,6 @@ def update(self, *args, **kwargs) -> None:
 
         for key, val in kwargs.items():
             self[key] = val
-        if len(kwargs) > 1 and _ODICT_TYPE is not dict:
-            warnings.warn(
-                "Before Python 3.7, initializing or updating a NocaseDict "
-                "object from more than one keyword argument is not guaranteed "
-                "to preserve their order",
-                UserWarning,
-                stacklevel=_stacklevel_above_nocasedict())
 
     def clear(self) -> None:
         """
@@ -723,8 +694,8 @@ def _raise_ordering_not_supported(self, other: Any, op: str) -> NoReturn:
         is not supported.
         """
         raise TypeError(
-            "'{}' not supported between instances of '{}' and '{}'".
-            format(op, type(self), type(other)))
+            f"'{op}' not supported between instances of '{type(self)}' and "
+            f"'{type(other)}'")
 
     def __lt__(self, other: Any) -> NoReturn:
         self._raise_ordering_not_supported(other, '<')
diff --git a/nocasedict/_utils.py b/nocasedict/_utils.py
deleted file mode 100644
index eaaec51..0000000
--- a/nocasedict/_utils.py
+++ /dev/null
@@ -1,33 +0,0 @@
-"""
-Utility functions of the nocasedict package.
-"""
-
-import inspect
-
-
-def _stacklevel_above_nocasedict() -> int:
-    """
-    Return the stack level (with 1 = caller of this function) of the first
-    caller that is not defined in the _nocasedict module and that is not
-    a method of a class named 'NocaseDict' (case insensitively). The second
-    check skips user classes derived from nocasedict.NocaseDict.
-
-    The returned stack level can be used directly by the caller of this
-    function as an argument for the stacklevel parameter of warnings.warn().
-    """
-    stacklevel = 2  # start with caller of our caller
-    frame = inspect.stack()[stacklevel][0]  # stack() level is 0-based
-    while True:
-        if frame.f_globals.get('__name__', None) != '_nocasedict':
-            try:
-                class_name = frame.f_locals['self'].__class__.__name__.lower()
-            except KeyError:
-                class_name = None
-            if class_name != 'nocasedict':
-                break
-        stacklevel += 1
-        if frame.f_back is None:
-            break
-        frame = frame.f_back
-    del frame
-    return stacklevel
diff --git a/setup.py b/setup.py
index 609fbe6..7a577d9 100755
--- a/setup.py
+++ b/setup.py
@@ -5,7 +5,6 @@
 
 import sys
 import os
-import io
 import re
 from typing import Optional
 
@@ -21,7 +20,7 @@ def get_version(version_file):
     requirements list of this package (otherwise it cannot be executed in
     a fresh Python environment).
     """
-    with io.open(version_file, 'r', encoding='utf-8') as fp:
+    with open(version_file, encoding='utf-8') as fp:
         version_source = fp.read()
     _globals = {}
     exec(version_source, _globals)  # pylint: disable=exec-used
@@ -34,7 +33,7 @@ def get_requirements(requirements_file):
     non-comment lines. The returned lines are without any trailing newline
     characters.
     """
-    with io.open(requirements_file, 'r', encoding='utf-8') as fp:
+    with open(requirements_file, encoding='utf-8') as fp:
         lines = fp.readlines()
     reqs = []
     for line in lines:
@@ -48,7 +47,7 @@ def read_file(a_file):
     """
     Read the specified file and return its content as one string.
     """
-    with io.open(a_file, 'r', encoding='utf-8') as fp:
+    with open(a_file, encoding='utf-8') as fp:
         content = fp.read()
     return content
 
diff --git a/tests/unittest/test_hashable.py b/tests/unittest/test_hashable.py
index 7b82b51..9e11399 100644
--- a/tests/unittest/test_hashable.py
+++ b/tests/unittest/test_hashable.py
@@ -2,7 +2,6 @@
 Test the HashableMixin mixin class.
 """
 
-from __future__ import absolute_import
 
 import os
 import pytest
@@ -155,7 +154,7 @@ def __hash__(self):
         "Comparing unicode value with bytes value",
         dict(
             obj1=MyNocaseDict([('k1', b'v1')]),
-            obj2=MyNocaseDict([('k2', u'v2')]),
+            obj2=MyNocaseDict([('k2', 'v2')]),
             exp_obj_equal=False,
         ),
         None, None, True
@@ -164,7 +163,7 @@ def __hash__(self):
         "Matching unicode key with string key",
         dict(
             obj1=MyNocaseDict([('k1', 'v1')]),
-            obj2=MyNocaseDict([(u'k2', 'v2')]),
+            obj2=MyNocaseDict([('k2', 'v2')]),
             exp_obj_equal=False,
         ),
         None, None, True
diff --git a/tests/unittest/test_keyableby.py b/tests/unittest/test_keyableby.py
index feae3ba..58746af 100644
--- a/tests/unittest/test_keyableby.py
+++ b/tests/unittest/test_keyableby.py
@@ -2,7 +2,6 @@
 Test the KeyableByMixin() mixin function.
 """
 
-from __future__ import absolute_import
 
 import os
 import pytest
diff --git a/tests/unittest/test_nocasedict.py b/tests/unittest/test_nocasedict.py
index 16ad7d3..11907e2 100755
--- a/tests/unittest/test_nocasedict.py
+++ b/tests/unittest/test_nocasedict.py
@@ -2,7 +2,6 @@
 Test the NocaseDict class.
 """
 
-from __future__ import absolute_import
 
 import sys
 import os
@@ -2679,7 +2678,7 @@ def test_NocaseDict_copy(testcase,
         "Comparing unicode value with bytes value",
         dict(
             obj1=NocaseDict([('k1', b'v1')]),
-            obj2=NocaseDict([('k2', u'v2')]),
+            obj2=NocaseDict([('k2', 'v2')]),
             exp_obj_equal=False,
         ),
         None, None, True
@@ -2688,7 +2687,7 @@ def test_NocaseDict_copy(testcase,
         "Matching unicode key with string key",
         dict(
             obj1=NocaseDict([('k1', 'v1')]),
-            obj2=NocaseDict([(u'k2', 'v2')]),
+            obj2=NocaseDict([('k2', 'v2')]),
             exp_obj_equal=False,
         ),
         None, None, True
diff --git a/tests/utils/import_installed.py b/tests/utils/import_installed.py
index b71f21f..e742edc 100644
--- a/tests/utils/import_installed.py
+++ b/tests/utils/import_installed.py
@@ -3,7 +3,6 @@
 package.
 """
 
-from __future__ import absolute_import, print_function
 
 import sys
 import os
@@ -79,11 +78,11 @@ def import_installed(module_name):
     if module_name not in sys.modules:
         module = __import__(module_name, level=0)  # only absolute imports
         if test_installed == 'DEBUG':
-            print("Debug: {0} module newly loaded from: {1}".
-                  format(module_name, module.__file__))
+            print(f"Debug: {module_name} module newly loaded from: "
+                  f"{module.__file__}")
     else:
         module = sys.modules[module_name]
         if test_installed == 'DEBUG':
-            print("Debug: {0} module was already loaded from: {1}".
-                  format(module_name, module.__file__))
+            print(f"Debug: {module_name} module was already loaded from: "
+                  f"{module.__file__}")
     return module
diff --git a/tests/utils/simplified_test_function.py b/tests/utils/simplified_test_function.py
index b31ef80..340eb8d 100644
--- a/tests/utils/simplified_test_function.py
+++ b/tests/utils/simplified_test_function.py
@@ -2,7 +2,6 @@
 simplified_test_function - Pytest extension for simplifying test functions.
 """
 
-from __future__ import absolute_import
 
 import functools
 import warnings
@@ -174,7 +173,7 @@ def wrapper_func(desc, kwargs, exp_exc_types, exp_warn_types, condition):
                         for w in rec_warnings:
                             tup = (w.filename, w.lineno, w.category.__name__,
                                    str(w.message))
-                            line = "{t[0]}:{t[1]}: {t[2]}: {t[3]}".format(t=tup)
+                            line = f"{tup[0]}:{tup[1]}: {tup[2]}: {tup[3]}"
                             if line not in lines:
                                 lines.append(line)
                         msg = "Unexpected warnings:\n{}".format(