The following mentioned code will work fine for converting list to a tuple in Python. You should keep one thing in mind that at the time of writing the code do not use tuple, list or other special names as a variable name.
l = [4,5,6]
Now discussing why you are getting that error the reason is, you've redefined tuple to be a tuple rather than the type tuple like as follows:
tuple = tuple(l)
Now you get a TypeError since the tuple itself is not callable:
TypeError: 'tuple' object is not callable
To overcome this error, You will have to recover the original definition for tuple by quitting and restarting your interpreter:-
Output:- <type 'tuple'>