diff --git a/.flake8 b/.flake8
index 3997777..ffb0b3b 100644
--- a/.flake8
+++ b/.flake8
@@ -1,4 +1,4 @@
 [flake8]
-ignore = C813
+ignore = C814
 import-order-style = google
 application-import-names = flask_annex
diff --git a/.gitignore b/.gitignore
index f2a536c..ba74660 100644
--- a/.gitignore
+++ b/.gitignore
@@ -55,6 +55,3 @@ docs/_build/
 
 # PyBuilder
 target/
-
-# Converted README for PyPI
-README.rst
diff --git a/.travis.yml b/.travis.yml
index f4a21f5..d5425b4 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,26 +1,20 @@
-sudo: false
+dist: xenial
 
 language: python
 python:
+  - "3.7"
   - "3.6"
-  - "pypy"
 
 env:
   - TOXENV=py-s3
 
 matrix:
   include:
-    - python: "3.6"
-      env: TOXENV=py-base
-    - # TODO: Remove this workaround once travis-ci/travis-ci#9815 is fixed.
-      sudo: true
-      dist: xenial
-      python: "3.7"
-      env: TOXENV=py-s3
-
-cache:
-  directories:
-    - $HOME/.cache/pip
+    - env: TOXENV=lint
+    - env: TOXENV=py-base
+    - python: pypy3
+
+cache: pip
 
 before_install:
   - pip install -U pip
diff --git a/flask_annex/__init__.py b/flask_annex/__init__.py
index 63dbd5e..2d6b698 100644
--- a/flask_annex/__init__.py
+++ b/flask_annex/__init__.py
@@ -11,7 +11,7 @@ def get_annex_class(storage):
         from .s3 import S3Annex
         return S3Annex
     else:
-        raise ValueError("unsupported storage {}".format(storage))
+        raise ValueError(f"unsupported storage {storage}")
 
 
 # -----------------------------------------------------------------------------
@@ -19,7 +19,7 @@ def get_annex_class(storage):
 
 # We don't use the base class here, as this is just a convenience thing rather
 # than an actual annex class.
-class Annex(object):
+class Annex:
     def __new__(cls, storage, *args, **kwargs):
         annex_class = get_annex_class(storage)
         return annex_class(*args, **kwargs)
@@ -30,7 +30,7 @@ def from_env(namespace):
 
         # Use storage-specific env namespace when configuring a generic annex,
         # to avoid having unrecognized extra keys when changing storage.
-        storage_namespace = '{}_{}'.format(namespace, storage.upper())
+        storage_namespace = f'{namespace}_{storage.upper()}'
 
         annex_class = get_annex_class(storage)
         return annex_class.from_env(storage_namespace)
diff --git a/flask_annex/base.py b/flask_annex/base.py
index 85c96cc..1ec6fd7 100644
--- a/flask_annex/base.py
+++ b/flask_annex/base.py
@@ -3,7 +3,7 @@
 # -----------------------------------------------------------------------------
 
 
-class AnnexBase(object):
+class AnnexBase:
     @classmethod
     def from_env(cls, namespace):
         return cls(**utils.get_config_from_env(namespace))
diff --git a/flask_annex/compat.py b/flask_annex/compat.py
deleted file mode 100644
index ef8d3c2..0000000
--- a/flask_annex/compat.py
+++ /dev/null
@@ -1,28 +0,0 @@
-import fnmatch
-import os
-import sys
-
-# -----------------------------------------------------------------------------
-
-PY2 = sys.version_info[0] == 2
-
-# -----------------------------------------------------------------------------
-
-if PY2:
-    string_types = (str, unicode)  # noqa: F821
-else:
-    string_types = (str,)
-
-# -----------------------------------------------------------------------------
-
-
-def recursive_glob(root_dir, pattern='*'):
-    """Search recursively for files matching a specified pattern.
-
-    Adapted from http://stackoverflow.com/questions/2186525/use-a-glob-to-find-files-recursively-in-python  # noqa: E501
-    """
-    return tuple(
-        os.path.join(root, filename)
-        for root, _dirnames, filenames in os.walk(root_dir)
-        for filename in fnmatch.filter(filenames, pattern)
-    )
diff --git a/flask_annex/file.py b/flask_annex/file.py
index 046fd88..514415e 100644
--- a/flask_annex/file.py
+++ b/flask_annex/file.py
@@ -5,7 +5,6 @@
 import flask
 
 from .base import AnnexBase
-from .compat import recursive_glob, string_types
 
 # -----------------------------------------------------------------------------
 
@@ -20,10 +19,8 @@ def _get_filename(self, key):
     def delete(self, key):
         try:
             os.unlink(self._get_filename(key))
-        except OSError as e:
-            if e.errno != errno.ENOENT:
-                # It's fine if the file doesn't exist.
-                raise  # pragma: no cover
+        except FileNotFoundError:
+            pass
 
         self._clean_empty_dirs(key)
 
@@ -34,11 +31,13 @@ def _clean_empty_dirs(self, key):
             dir_name = self._get_filename(key_dir_name)
             try:
                 os.rmdir(dir_name)
+            except FileNotFoundError:
+                pass
             except OSError as e:
                 if e.errno == errno.ENOTEMPTY:
                     break
-                if e.errno != errno.ENOENT:
-                    raise  # pragma: no cover
+
+                raise  # pragma: no cover
 
             key_dir_name = os.path.dirname(key_dir_name)
 
@@ -49,7 +48,7 @@ def delete_many(self, keys):
     def get_file(self, key, out_file):
         in_filename = self._get_filename(key)
 
-        if isinstance(out_file, string_types):
+        if isinstance(out_file, str):
             shutil.copyfile(in_filename, out_file)
         else:
             with open(in_filename, 'rb') as in_fp:
@@ -57,7 +56,15 @@ def get_file(self, key, out_file):
 
     def list_keys(self, prefix):
         root = self._get_filename(prefix)
-        filenames = (root,) if os.path.isfile(root) else recursive_glob(root)
+        filenames = (
+            (root,)
+            if os.path.isfile(root)
+            else tuple(
+                os.path.join(root, filename)
+                for root, _dirnames, filenames in os.walk(root)
+                for filename in filenames
+            )
+        )
 
         return tuple(
             os.path.relpath(filename, self._root_path)
@@ -68,7 +75,7 @@ def save_file(self, key, in_file):
         out_filename = self._get_filename(key)
         self._ensure_key_dir(key)
 
-        if isinstance(in_file, string_types):
+        if isinstance(in_file, str):
             shutil.copyfile(in_file, out_filename)
         else:
             with open(out_filename, 'wb') as out_fp:
@@ -81,15 +88,11 @@ def _ensure_key_dir(self, key):
 
         # Verify that we aren't trying to create the root path.
         if not os.path.exists(self._root_path):
-            raise IOError(
-                "root path {} does not exist".format(self._root_path),
+            raise FileNotFoundError(
+                f"root path {self._root_path} does not exist",
             )
 
-        try:
-            os.makedirs(dir_name)
-        except OSError as e:  # pragma: no cover
-            if e.errno != errno.EEXIST:
-                raise
+        os.makedirs(dir_name, exist_ok=True)
 
     def send_file(self, key):
         return flask.send_from_directory(
diff --git a/flask_annex/s3.py b/flask_annex/s3.py
index 9934c2a..fdc28fe 100644
--- a/flask_annex/s3.py
+++ b/flask_annex/s3.py
@@ -4,7 +4,6 @@
 import flask
 
 from .base import AnnexBase
-from .compat import string_types
 
 # -----------------------------------------------------------------------------
 
@@ -19,6 +18,7 @@ class S3Annex(AnnexBase):
     def __init__(
         self,
         bucket_name,
+        *,
         region=None,
         access_key_id=None,
         secret_access_key=None,
@@ -43,8 +43,7 @@ def delete_many(self, keys):
         # casting to tuple because keys might be iterable
         objects = tuple({'Key': key} for key in keys)
         if not objects:
-            # this is not just an optimization, boto fails if the array
-            # is empty
+            # boto fails if the array is empty.
             return
 
         self._client.delete_objects(
@@ -53,7 +52,7 @@ def delete_many(self, keys):
         )
 
     def get_file(self, key, out_file):
-        if isinstance(out_file, string_types):
+        if isinstance(out_file, str):
             self._client.download_file(self._bucket_name, key, out_file)
         else:
             self._client.download_fileobj(self._bucket_name, key, out_file)
@@ -77,7 +76,7 @@ def save_file(self, key, in_file):
         else:
             extra_args = None
 
-        if isinstance(in_file, string_types):
+        if isinstance(in_file, str):
             self._client.upload_file(
                 in_file, self._bucket_name, key, extra_args,
             )
diff --git a/flask_annex/utils.py b/flask_annex/utils.py
index 25631a3..356ce6b 100644
--- a/flask_annex/utils.py
+++ b/flask_annex/utils.py
@@ -4,7 +4,7 @@
 
 
 def get_config_from_env(namespace):
-    prefix = '{}_'.format(namespace)
+    prefix = f'{namespace}_'
 
     return {
         key[len(prefix):].lower(): value
diff --git a/setup.cfg b/setup.cfg
index d8673a6..bd6a4ac 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -2,4 +2,5 @@
 universal = 1
 
 [metadata]
-long_description = file: README.rst
+long_description = file: README.md
+long_description_content_type = text/markdown
diff --git a/setup.py b/setup.py
index 41d351f..ae46108 100644
--- a/setup.py
+++ b/setup.py
@@ -31,7 +31,8 @@ def run(self):
     author="Jimmy Jia",
     author_email='tesrin@gmail.com',
     license='MIT',
-    classifiers=(
+    python_requires=">=3.6",
+    classifiers=[
         'Development Status :: 2 - Pre-Alpha',
         'Framework :: Flask',
         'Environment :: Web Environment',
@@ -40,9 +41,12 @@ def run(self):
         'Operating System :: OS Independent',
         'Programming Language :: Python',
         'Programming Language :: Python :: 3',
+        'Programming Language :: Python :: 3.6',
+        'Programming Language :: Python :: 3.7',
+        'Programming Language :: Python :: 3 :: Only',
         'Topic :: Internet :: WWW/HTTP :: Dynamic Content',
         'Topic :: Software Development :: Libraries :: Python Modules',
-    ),
+    ],
     keywords='storage s3 flask',
     packages=('flask_annex',),
     install_requires=(
@@ -50,17 +54,13 @@ def run(self):
     ),
     extras_require={
         's3': ('boto3 >= 1.4.0',),
-        'tests': (
-            'mock',
-            'moto',
-            'pytest',
-            'requests',
-        ),
+        'lint': ('flake8', 'flake8-config-4catalyzer'),
+        'tests': ('pytest', 'pytest-cov'),
+        'tests-s3': ('moto', 'requests'),
     },
     cmdclass={
         'clean': system('rm -rf build dist *.egg-info'),
-        'package': system('python setup.py pandoc sdist bdist_wheel'),
-        'pandoc': system('pandoc README.md -o README.rst'),
+        'package': system('python setup.py sdist bdist_wheel'),
         'publish': system('twine upload dist/*'),
         'release': system('python setup.py clean package publish'),
         'test': system('tox'),
diff --git a/tests/helpers.py b/tests/helpers.py
index 2bf743c..8a5fd3e 100644
--- a/tests/helpers.py
+++ b/tests/helpers.py
@@ -16,14 +16,14 @@ def assert_key_value(annex, key, value):
 
 
 def get_upload_info(client, key, **kwargs):
-    response = client.get('/upload_info/{}'.format(key), **kwargs)
+    response = client.get(f'/upload_info/{key}', **kwargs)
     return json.loads(response.get_data(as_text=True))
 
 
 # -----------------------------------------------------------------------------
 
 
-class AbstractTestAnnex(object):
+class AbstractTestAnnex:
     @pytest.fixture
     def annex(self, annex_base):
         annex_base.save_file('foo/bar.txt', BytesIO(b'1\n'))
diff --git a/tests/test_s3.py b/tests/test_s3.py
index c985fd0..07b1139 100644
--- a/tests/test_s3.py
+++ b/tests/test_s3.py
@@ -1,8 +1,8 @@
 import base64
 from io import BytesIO
 import json
+from unittest.mock import Mock
 
-from mock import Mock
 import pytest
 
 from flask_annex import Annex
diff --git a/tox.ini b/tox.ini
index cc54f9a..5beb3ed 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,22 +1,18 @@
 [tox]
-envlist = py{36,37}-{base,s3}
+envlist =
+    lint
+    py{36,37}-{base,s3}
 
 [testenv]
 usedevelop = True
-
 deps =
-    flake8
-    flake8-config-4catalyzer
-    mock
-    pytest
-    pytest-cov
-
     s3: moto
     s3: requests
-
 extras =
-    s3: s3
+    tests
+    s3: s3, tests-s3
+commands = pytest --cov {posargs}
 
-commands =
-    flake8 .
-    pytest --cov
+[testenv:lint]
+extras = lint
+commands = flake8 .