> It might help if the error message also stated how many arguments were actually received, like the TypeError message already does for bad function / method calls.  E.g., 
> 
> "struct.error: pack expected 2 items for packing (got 1)"

Yes, this would be useful. But seldom implemented.

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: not enough arguments for format string
>>> '%s %s'%(123,456,789)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: not all arguments converted during string formatting

struct.pack also inconsistent in other error messages.

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
struct.error: argument for 's' must be a bytes object
>>> struct.pack('i', '123')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
struct.error: required argument is not an integer

For "s" is mentioned format, and for "i" no. It would be helpful to
mention also the number of the item.