No dependencies listed in setup.py

According to the setup.py file, this package has no dependencies, which is unfortunately not the case:

$ python3 -m venv venv
$ ./venv/bin/python -m pip install .
Processing /home/duncan/git/dttxml
Using legacy 'setup.py install' for dttxml, since package 'wheel' is not installed.
Installing collected packages: dttxml
    Running setup.py install for dttxml ... done
Successfully installed dttxml-1.1.0
$ ./venv/bin/dtt2hdf --help
Traceback (most recent call last):
  File "./venv/bin/dtt2hdf", line 33, in <module>
    sys.exit(load_entry_point('dttxml==1.1.0', 'console_scripts', 'dtt2hdf')())
  File "./venv/bin/dtt2hdf", line 25, in importlib_load_entry_point
    return next(matches).load()
  File "/home/duncan/opt/miniconda3/lib/python3.8/importlib/metadata.py", line 77, in load
    module = import_module(match.group('module'))
  File "/home/duncan/opt/miniconda3/lib/python3.8/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1014, in _gcd_import
  File "<frozen importlib._bootstrap>", line 991, in _find_and_load
  File "<frozen importlib._bootstrap>", line 961, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "<frozen importlib._bootstrap>", line 1014, in _gcd_import
  File "<frozen importlib._bootstrap>", line 991, in _find_and_load
  File "<frozen importlib._bootstrap>", line 975, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 671, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 783, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/home/duncan/git/dttxml/venv/lib/python3.8/site-packages/dttxml/__init__.py", line 5, in <module>
    from .parse import dtt_read
  File "/home/duncan/git/dttxml/venv/lib/python3.8/site-packages/dttxml/parse.py", line 4, in <module>
    import numpy as np
ModuleNotFoundError: No module named 'numpy'

The install_requires keyword to the setuptools.setup command needs to be populated with all of the non-optional requirements.