Deprecation warning for Python 2; pytest<5 (#877)

* Deprecation warning for Python 2
* Update test instructions to pytest<5 for Python 2

doc/getting_started.rst

@@ -77,7 +77,7 @@ Prerequisites
    * gdcm
    * jpeg_ls
    * jpeg2000
-   * pytest (if running pydicom's test suite)
+   * pytest (if running pydicom's test suite). pytest<5 if in Python 2.
 
 
 Installing pydicom
@@ -139,6 +139,8 @@ pydicom's setup.py file and::
 
 This will install `pytest <https://pytest.org>`_ if it is not 
 already installed.
+
+In v1.3 run under Python 2, if pytest is not found, please `python2 -m pip install "pytest<5"`
 
 Or, in linux you can also use::
 

pydicom/__init__.py

@@ -47,3 +47,9 @@
            'write_file',
            '__version__',
            '__version_info__']
+
+from pydicom.compat import in_py2
+if in_py2:
+    import warnings
+    msg = 'Python 2 will no longer be supported after the pydicom v1.4 release'
+    warnings.warn(msg, DeprecationWarning)

setup.py

@@ -22,6 +22,9 @@
 
 needs_pytest = {'pytest', 'test', 'ptr'}.intersection(sys.argv)
 pytest_runner = ['pytest-runner'] if needs_pytest else []
+
+# in_py2 check in next line - pytest>=5 requires Python 3
+TESTS_REQUIRE = ['pytest<5'] if sys.version_info[0] == 2 else ['pytest']
 _py_modules = []
 if not have_dicom:
     _py_modules = ['dicom']
@@ -56,7 +59,6 @@
 VERSION = __version__
 REQUIRES = []
 SETUP_REQUIRES = pytest_runner
-TESTS_REQUIRE = ['pytest']
 
 # get long description from README.md
 BASE_PATH = os.path.abspath(os.path.dirname(__file__))