If you actually need a deep learning model, PyTorch and TensorFlow are both good choices. Topics ... by subclassing keras.Model, but prefers the functional API when possible.

While eager execution mode is a fairly new option in TensorFlow, it’s the only way PyTorch runs: API calls execute when invoked, rather than being added to a graph to be run later.

Put another way, you write Keras code using Python. The Keras code calls into the TensorFlow library, which does all the work. In Keras terminology, TensorFlow is the called backend engine.