diff --git a/CONTRIBUTING.rst b/CONTRIBUTING.rst
index 2be5977..ddda924 100644
--- a/CONTRIBUTING.rst
+++ b/CONTRIBUTING.rst
@@ -55,9 +55,9 @@ If you are proposing a feature:
 Get Started!
 ------------
 
-Ready to contribute? Here's how to set up `conda-devenv` for local development.
+Ready to contribute? Here's how to set up ``conda-devenv`` for local development.
 
-1. Fork the `conda-devenv` repo on GitHub.
+1. Fork the ``conda-devenv`` repo on GitHub.
 2. Clone your fork locally::
 
     $ git clone git@github.com:your_name_here/conda-devenv.git
@@ -65,7 +65,8 @@ Ready to contribute? Here's how to set up `conda-devenv` for local development.
 3. Create a new conda environment for developing::
 
     $ conda create -n devenv --file requirements_dev.txt
-    $ conda develop conda_devenv
+    $ source activate devenv
+    $ pip install -e .
 
 4. Create a branch for local development::
 
diff --git a/conda_devenv/devenv.py b/conda_devenv/devenv.py
index 8591c61..4e43d3a 100644
--- a/conda_devenv/devenv.py
+++ b/conda_devenv/devenv.py
@@ -48,7 +48,7 @@ def handle_includes(root_filename, root_yaml):
                     ))
             with open(included_filename, "r") as f:
                 jinja_contents = render_jinja(f.read(), included_filename)
-            included_yaml_dict = yaml.load(jinja_contents)
+            included_yaml_dict = yaml.safe_load(jinja_contents)
             if included_yaml_dict is None:
                 raise ValueError("The file '{included_filename}' which was"
                                  " included by '{filename}' is empty."
@@ -329,7 +329,6 @@ def write_activate_deactivate_scripts(args, conda_yaml_dict, environment):
     info = json.loads(info)
     envs = info["envs"]
 
-    env_directory = None
     for env in envs:
         if os.path.basename(env) == env_name:
             env_directory = env
@@ -376,12 +375,21 @@ def main(args=None):
                                              "includes the 'environment' section.", action="store_true")
     parser.add_argument("--no-prune", help="Don't pass --prune flag to conda-env.", action="store_true")
     parser.add_argument("--output-file", nargs="?", help="Output filename.")
-    parser.add_argument("--quiet", action="store_true", default=False)
+    parser.add_argument("--quiet", action="store_true", default=False, help="Do not show progress")
+    parser.add_argument("--version", action="store_true", default=False, help="Show version and exit")
 
     args = parser.parse_args(args)
 
+    if args.version:
+        from ._version import version
+        print('conda-devenv version {0}'.format(version))
+        return 0
+
     filename = args.file
     filename = os.path.abspath(filename)
+    if not os.path.isfile(filename):
+        print('File "{0}" does not exist.'.format(filename), file=sys.stderr)
+        return 1
 
     is_devenv_input_file = filename.endswith('.devenv.yml')
     if is_devenv_input_file:
diff --git a/requirements_dev.txt b/requirements_dev.txt
index a41d034..c2c73e0 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -8,6 +8,6 @@ coverage
 Sphinx
 cryptography
 PyYAML
-pytest
+pytest >= 3
 pytest-datadir >= 1.0
 pytest-mock
diff --git a/setup.py b/setup.py
index c8e4a86..158e834 100644
--- a/setup.py
+++ b/setup.py
@@ -52,6 +52,7 @@ setup(
         'Programming Language :: Python :: 3',
         'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
+        'Programming Language :: Python :: 3.6',
     ],
     test_suite='tests',
     tests_require=test_requirements

Add --version flag
diff --git a/tests/test_main.py b/tests/test_main.py
index feb2425..f1e1a27 100644
--- a/tests/test_main.py
+++ b/tests/test_main.py
@@ -90,3 +90,27 @@ def test_print_full(tmpdir, capsys):
     assert 'environment:' in out
     assert 'PYTHONPATH:' in out
 
+
+def test_version(capsys):
+    """
+    Test --version flag.
+    """
+    from conda_devenv._version import version
+    assert devenv.main(['--version']) == 0
+    out, err = capsys.readouterr()
+    assert err == ''
+    assert version in out
+
+    import conda_devenv
+    assert conda_devenv.__version__ == version
+
+
+@pytest.mark.parametrize('explicit_file', [True, False])
+def test_error_message_environment_file_not_found(capsys, tmpdir, explicit_file, monkeypatch):
+    monkeypatch.chdir(str(tmpdir))
+    args = ['--file', 'invalid.devenv.yml'] if explicit_file else []
+    expected_name = 'invalid.devenv.yml' if explicit_file else 'environment.devenv.yml'
+    assert devenv.main(args) == 1
+    out, err = capsys.readouterr()
+    assert out == ''
+    assert err == 'File "{0}" does not exist.\n'.format(str(tmpdir / expected_name))

pip install -e .[dev]
parse_log_pytest
requirements.txt
pytest pytest-datadir
3.6
requirements_dev.txt
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
alabaster==0.7.13
attrs==22.2.0
Babel==2.11.0
bump2version==1.0.1
bumpversion==0.6.0
certifi==2021.5.30
cffi==1.15.1
charset-normalizer==2.0.12
-e git+https://github.com/ESSS/conda-devenv.git@7867067acadb89f7da61af330d85caa31b284dd8#egg=conda_devenv
coverage==6.2
cryptography==40.0.2
distlib==0.3.9
docutils==0.17.1
filelock==3.4.1
flake8==5.0.4
idna==3.10
imagesize==1.4.1
importlib-metadata==4.2.0
importlib-resources==5.4.0
iniconfig==1.1.1
Jinja2==3.0.3
MarkupSafe==2.0.1
mccabe==0.7.0
packaging==21.3
platformdirs==2.4.0
pluggy==1.0.0
py==1.11.0
pycodestyle==2.9.1
pycparser==2.21
pyflakes==2.5.0
Pygments==2.14.0
pyparsing==3.1.4
pytest==7.0.1
pytest-datadir==1.4.1
pytest-mock==3.6.1
pytz==2025.2
PyYAML==6.0.1
requests==2.27.1
six==1.17.0
snowballstemmer==2.2.0
Sphinx==4.3.2
sphinxcontrib-applehelp==1.0.2
sphinxcontrib-devhelp==1.0.2
sphinxcontrib-htmlhelp==2.0.0
sphinxcontrib-jsmath==1.0.1
sphinxcontrib-qthelp==1.0.3
sphinxcontrib-serializinghtml==1.1.5
toml==0.10.2
tomli==1.2.3
tox==3.28.0
typing_extensions==4.1.1
urllib3==1.26.20
virtualenv==20.16.2
watchdog==2.3.1
zipp==3.6.0

name: conda-devenv
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - certifi=2021.5.30=py36h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.3=he6710b0_2
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=1.1.1w=h7f8727e_0
  - pip=21.2.2=py36h06a4308_0
  - python=3.6.13=h12debd9_1
  - readline=8.2=h5eee18b_0
  - setuptools=58.0.4=py36h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - wheel=0.37.1=pyhd3eb1b0_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - alabaster==0.7.13
      - attrs==22.2.0
      - babel==2.11.0
      - bump2version==1.0.1
      - bumpversion==0.6.0
      - cffi==1.15.1
      - charset-normalizer==2.0.12
      - coverage==6.2
      - cryptography==40.0.2
      - distlib==0.3.9
      - docutils==0.17.1
      - filelock==3.4.1
      - flake8==5.0.4
      - idna==3.10
      - imagesize==1.4.1
      - importlib-metadata==4.2.0
      - importlib-resources==5.4.0
      - iniconfig==1.1.1
      - jinja2==3.0.3
      - markupsafe==2.0.1
      - mccabe==0.7.0
      - packaging==21.3
      - platformdirs==2.4.0
      - pluggy==1.0.0
      - py==1.11.0
      - pycodestyle==2.9.1
      - pycparser==2.21
      - pyflakes==2.5.0
      - pygments==2.14.0
      - pyparsing==3.1.4
      - pytest==7.0.1
      - pytest-datadir==1.4.1
      - pytest-mock==3.6.1
      - pytz==2025.2
      - pyyaml==6.0.1
      - requests==2.27.1
      - six==1.17.0
      - snowballstemmer==2.2.0
      - sphinx==4.3.2
      - sphinxcontrib-applehelp==1.0.2
      - sphinxcontrib-devhelp==1.0.2
      - sphinxcontrib-htmlhelp==2.0.0
      - sphinxcontrib-jsmath==1.0.1
      - sphinxcontrib-qthelp==1.0.3
      - sphinxcontrib-serializinghtml==1.1.5
      - toml==0.10.2
      - tomli==1.2.3
      - tox==3.28.0
      - typing-extensions==4.1.1
      - urllib3==1.26.20
      - virtualenv==20.16.2
      - watchdog==2.3.1
      - zipp==3.6.0
prefix: /opt/conda/envs/conda-devenv

tests/test_main.py::test_version tests/test_main.py::test_error_message_environment_file_not_found[True] tests/test_main.py::test_error_message_environment_file_not_found[False]
tests/test_main.py::test_handle_input_file[True-environment.devenv.yml-1] tests/test_main.py::test_handle_input_file[False-environment.devenv.yml-1] tests/test_main.py::test_print[environment.devenv.yml] tests/test_main.py::test_print_full
tests/test_main.py::test_handle_input_file[True-environment.yml-0] tests/test_main.py::test_handle_input_file[False-environment.yml-0] tests/test_main.py::test_print[environment.yml]
setup.py requirements_dev.txt conda_devenv/devenv.py CONTRIBUTING.rst
setup.py requirements_dev.txt conda_devenv/devenv.py CONTRIBUTING.rst