PythonPackage: add pypi attribute to infer homepage/url/list_url (#17587)

var/spack/repos/builtin/packages/py-matplotlib/package.py

@@ -11,7 +11,7 @@ class PyMatplotlib(PythonPackage):
     and interactive visualizations in Python."""
 
     homepage = "https://matplotlib.org/"
-    url      = "https://pypi.io/packages/source/m/matplotlib/matplotlib-3.3.2.tar.gz"
+    pypi     = "matplotlib/matplotlib-3.3.2.tar.gz"
 
     maintainers = ['adamjstewart']
     import_modules = [

var/spack/repos/builtin/packages/py-numpy/package.py

@@ -16,7 +16,7 @@ class PyNumpy(PythonPackage):
     number capabilities"""
 
     homepage = "https://numpy.org/"
-    url      = "https://pypi.io/packages/source/n/numpy/numpy-1.19.4.zip"
+    pypi     = "numpy/numpy-1.19.4.zip"
     git      = "https://github.com/numpy/numpy.git"
 
     maintainers = ['adamjstewart']

var/spack/repos/builtin/packages/py-scipy/package.py

@@ -12,7 +12,7 @@ class PyScipy(PythonPackage):
     as routines for numerical integration and optimization."""
 
     homepage = "https://www.scipy.org/"
-    url      = "https://pypi.io/packages/source/s/scipy/scipy-1.5.4.tar.gz"
+    pypi     = "scipy/scipy-1.5.4.tar.gz"
     git      = "https://github.com/scipy/scipy.git"
 
     maintainers = ['adamjstewart']