I have a NumPy array that is of size (3, 3). When I print shape of the array within __main__ module I get (3, 3). However I am passing this array to a function and when I print its size in the function I get (3, ).
Why does this happen?
Also, what does it mean for a tuple to have its last element unspecified? That is, shouldn't (3, ) be an invalid tuple in the first place?
To answer your second question:
Tuples in Python are n-dimensional. That is you can have a 1-2-3-...-n tuple. Due to syntax, the way you represent a 1-dimensional tuple is ('element',) where the trailing comma is mandatory. If you have ('element') then this is just simply the expression inside the parenthesis. So (3) + 4 == 7, but (3,) + 4 == TypeError. Likewise ('element') == 'element'.
To answer your first question:
You're more than likely doing something wrong with passing the array around. There is no reason for the NumPy array to misrepresent itself without some type of mutation to the array.
A tuple like this: (3, ) means that it's a tuple with a single element (a single dimension, in this case). That's the correct syntax - with a trailing , because if it looked like this: (3) then Python would interpret it as a number surrounded by parenthesis, not a tuple.
It'd be useful to see the actual code, but I'm guessing that you're not passing the entire array, only a row (or a column) of it.
It is hard to tell why a function call would reshape a numpy array without seeing the code.
On the second question, that is the standard notation for a single-element tuple - the comma, rather than the brackets, is what makes it a tuple. Consider (3+3) * 2 - if the brackets made a tuple, then that whole expression would be invalid since you can't multiply a tuple by an int. More generally, Python allows trailing commas all over the place:
>>> (3,3,) == (3,3)
True
This also works for lists, dictionaries and function calls - basically, everywhere where Python expects comma-separated elements, a trailing comma is valid.
x = (3, )gives you a tuple,x=(3)will not give you a tuple