Handle pipenv like version restrictions

We need to handle python_version filters in requirement files in order
to install cleanly using pip

setup.py

@@ -15,6 +15,8 @@ import os
 import sys
 import glob
 import time
+import operator
+import platform
 try:
     from urllib2 import urlopen
 except ImportError:
@@ -136,6 +138,74 @@ exec(compile(open(SALT_VERSION).read(), SALT_VERSION, 'exec'))
 
 
 # ----- Helper Functions -------------------------------------------------------------------------------------------->
+
+def _parse_op(op):
+    '''
+    >>> _parse_op('>')
+    'gt'
+    >>> _parse_op('>=')
+    'ge'
+    >>> _parse_op('=>')
+    'ge'
+    >>> _parse_op('=> ')
+    'ge'
+    >>> _parse_op('<')
+    'lt'
+    >>> _parse_op('<=')
+    'le'
+    >>> _parse_op('==')
+    'eq'
+    >>> _parse_op(' <= ')
+    'le'
+    '''
+    op = op.strip()
+    if '>' in op:
+        if '=' in op:
+            return 'ge'
+        else:
+            return 'gt'
+    elif '<' in op:
+        if '=' in op:
+            return 'le'
+        else:
+            return 'lt'
+    elif '!' in op:
+        return 'ne'
+    else:
+        return 'eq'
+
+
+def _parse_ver(ver):
+    '''
+    >>> _parse_ver("'3.4'  # pyzmq 17.1.0 stopped building wheels for python3.4")
+    '3.4'
+    >>> _parse_ver('"3.4"')
+    '3.4'
+    >>> _parse_ver('"2.6.17"')
+    '2.6.17'
+    '''
+    if '#' in ver:
+        ver, _ = ver.split('#', 1)
+        ver = ver.strip()
+    return ver.strip('\'').strip('"')
+
+
+def _check_ver(pyver, op, wanted):
+    '''
+    >>> _check_ver('2.7.15', 'gt', '2.7')
+    True
+    >>> _check_ver('2.7.15', 'gt', '2.7.15')
+    False
+    >>> _check_ver('2.7.15', 'ge', '2.7.15')
+    True
+    >>> _check_ver('2.7.15', 'eq', '2.7.15')
+    True
+    '''
+    pyver = distutils.version.LooseVersion(pyver)
+    wanted = distutils.version.LooseVersion(wanted)
+    return getattr(operator, '__{}__'.format(op))(pyver, wanted)
+
+
 def _parse_requirements_file(requirements_file):
     parsed_requirements = []
     with open(requirements_file) as rfh:
@@ -150,7 +220,16 @@ def _parse_requirements_file(requirements_file):
                 # Python 3 already has futures, installing it will only break
                 # the current python installation whenever futures is imported
                 continue
-            parsed_requirements.append(line)
+            try:
+                pkg, pyverspec = line.rsplit(';', 1)
+            except ValueError:
+                pkg, pyverspec = line, ''
+            pyverspec = pyverspec.strip()
+            if pyverspec:
+                _, op, ver = pyverspec.split(' ', 2)
+                if not _check_ver(platform.python_version(), _parse_op(op), _parse_ver(ver)):
+                    continue
+            parsed_requirements.append(pkg)
     return parsed_requirements
 # <---- Helper Functions ---------------------------------------------------------------------------------------------
 
@@ -362,7 +441,6 @@ class DownloadWindowsDlls(Command):
         if getattr(self.distribution, 'salt_download_windows_dlls', None) is None:
             print('This command is not meant to be called on it\'s own')
             exit(1)
-        import platform
         import pip
         # pip has moved many things to `_internal` starting with pip 10
         if LooseVersion(pip.__version__) < LooseVersion('10.0'):
@@ -932,7 +1010,6 @@ class SaltDistribution(distutils.dist.Distribution):
 
         if IS_WINDOWS_PLATFORM:
             install_requires = _parse_requirements_file(SALT_WINDOWS_REQS)
-
         return install_requires
 
     @property