The make install step fails with this error:

Traceback (most recent call last):
  File "/home/dandan/Downloads/cpython-3.7.0a1/Lib/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/home/dandan/Downloads/cpython-3.7.0a1/Lib/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/dandan/Downloads/cpython-3.7.0a1/Lib/ensurepip/__main__.py", line 4, in <module>
    ensurepip._main()
  File "/home/dandan/Downloads/cpython-3.7.0a1/Lib/ensurepip/__init__.py", line 189, in _main
    default_pip=args.default_pip,
  File "/home/dandan/Downloads/cpython-3.7.0a1/Lib/ensurepip/__init__.py", line 102, in bootstrap
    _run_pip(args + [p[0] for p in _PROJECTS], additional_paths)
  File "/home/dandan/Downloads/cpython-3.7.0a1/Lib/ensurepip/__init__.py", line 27, in _run_pip
    import pip
  File "/tmp/tmpcg658x_c/pip-9.0.1-py2.py3-none-any.whl/pip/__init__.py", line 28, in <module>
  File "/tmp/tmpcg658x_c/pip-9.0.1-py2.py3-none-any.whl/pip/vcs/mercurial.py", line 9, in <module>
  File "/tmp/tmpcg658x_c/pip-9.0.1-py2.py3-none-any.whl/pip/download.py", line 36, in <module>
  File "/tmp/tmpcg658x_c/pip-9.0.1-py2.py3-none-any.whl/pip/utils/glibc.py", line 4, in <module>
  File "/home/dandan/Downloads/cpython-3.7.0a1/Lib/ctypes/__init__.py", line 7, in <module>
    from _ctypes import Union, Structure, Array
ModuleNotFoundError: No module named '_ctypes'
Makefile:1080: recipe for target 'install' failed
make: *** [install] Error 1

Am I missing something?