I find it useful for _ to contain the value fo the last result. However, I sometimes want to use _ to suppress the printing of the return argument of a function call. Unfortunately, once _ has been assigned to, it stops taking on the value of the last result:
2+3 # Console output: 5
_ # Console output: 5
_=3+4 # Explicitly assign to "_"
_ # Console output: 7
4+5 # Console output: 9
_ # Console output: 7
In the last line, the default behaviour is for _ to contain the last result 9. However, it retains the 2nd last result instead because it was explicitly assigned to. Let's refer to this as a non-default behaviour, i.e. retaining the value explicitly assigned to _ rather than _ storing the result of the last evaluated expression that was not assigned to a variable.
(1) How else can one selectively suppress console output besides assigning it to a throw-away variable like _? I can assign to another variable (say) dum, but I don't want to constantly issue del dum to keep the Variable Explorer clean and memory free.
(2) Also, once I've explicitly assigned to _, is there any way to get back the default behaviour of having it take on the last result? Issuing del _ doesn't do so.
Note: My previous Q&A simply recognizes the non-default behaviour as the explanation for an error. It doesn't provide a solution.
(1) To suppress console output in IPython, you can add a semicolon
In [1]: 3+1;
In [2]:
(2) In Python shell, setting _ would stop python from setting it to the last result, del _ would revert this as expected.
But in IPython shell, if any of the variables _, __, ___ are "out-of-sync", they won't be set to the last 3 results. So to revert any change of _, need to del _,__,___.