TypeError: 'Tensor' object is not callable

可能是 keras 的用法？

Traceback (most recent call last):
  File "c:\Users\MisakiSakura\.vscode-oss\extensions\ms-python.python-2020.2.64397\pythonFiles\ptvsd_launcher.py", line 48, in <module>
    main(ptvsdArgs)
  File "c:\Users\MisakiSakura\.vscode-oss\extensions\ms-python.python-2020.2.64397\pythonFiles\lib\python\old_ptvsd\ptvsd\__main__.py", line 432, in main
    run()
  File "c:\Users\MisakiSakura\.vscode-oss\extensions\ms-python.python-2020.2.64397\pythonFiles\lib\python\old_ptvsd\ptvsd\__main__.py", line 316, in run_file
    runpy.run_path(target, run_name='__main__')
  File "C:\Users\MisakiSakura\AppData\Local\Programs\Python\Python37\lib\runpy.py", line 263, in run_path
    pkg_name=pkg_name, script_name=fname)
  File "C:\Users\MisakiSakura\AppData\Local\Programs\Python\Python37\lib\runpy.py", line 96, in _run_module_code
    mod_name, mod_spec, pkg_name, script_name)
  File "C:\Users\MisakiSakura\AppData\Local\Programs\Python\Python37\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "d:\Code\tensorflow-homework\02. linear-regression-with-one-variable\main.py", line 46, in <module>
    optimizer = tf.optimizers.SGD(learning_rate).minimize(loss_function, var_list=[w, b])
  File "D:\Code\tensorflow-homework\venv\lib\site-packages\tensorflow_core\python\keras\optimizer_v2\optimizer_v2.py", line 316, in minimize
    loss, var_list=var_list, grad_loss=grad_loss)
  File "D:\Code\tensorflow-homework\venv\lib\site-packages\tensorflow_core\python\keras\optimizer_v2\optimizer_v2.py", line 350, in _compute_gradients
    loss_value = loss()
TypeError: 'Tensor' object is not callable