When using Python Tensorflow input shape (53,))... what's going on with this comma?

Question

I'm confused by the following line of code:

input_img = Input(shape=(53,))

I have a batch of 52 images but how can a tuple have nothing after the comma? What does this mean?

Answer 1

The function Input excepts a tuple for the argument shape

Using the comma allows you to define a tuple with a single item. If you simply used (53) or 53, it would be interpreted as an integer:

type( 53 )
<class 'int'>
type( (53) )
<class 'int'>
type( (53,) )
<class 'tuple'>

This is because the simple brackets are used in computations hence cannot be parsed a tuples:

(53) + 2 # would raise an error if (53) was a tuple
(53 + 1)*2 # would also raise an error if (53+1) was a tuple

So in order to define a tuple with a single item, you have to add the comma: (53,)