Workaround the changes to pip internals

Author: createdbysk

setup.py

@@ -7,7 +7,14 @@
 except ImportError:
     # It is quick hack to support pip 10 that has changed its internal
     # structure of the modules.
-    from pip._internal.download import PipSession
+    # Further hack - seems like pip 20 and later does not support
+    # pip._internal.download anymore. It appears as though 
+    # parse_requirements (used below) does not need a valid PipSession. 
+    # Any value seems to work. So hack this even more.
+    try: 
+        from pip._internal.download import PipSession
+    except ImportError:
+        PipSession = object
     from pip._internal.req.req_file import parse_requirements
 
 
@@ -22,9 +29,12 @@ def get_requirements(source):
     """
 
     install_reqs = parse_requirements(filename=source, session=PipSession())
-
-    return [str(ir.req) for ir in install_reqs]
-
+    # pip 20 changed ParsedRequirement.req to ParsedRequirement.requirement.
+    try:
+        requirements = [str(ir.req) for ir in install_reqs]
+    except AttributeError:
+        requirements = [str(ir.requirement) for ir in install_reqs]
+    return requirements
 
 setup(
     packages=find_packages(),