function argument dependent on another function argument?

[Paul Rubin]

Steven D'Aprano <steve at REMOVE-THIS-cybersource.com.au> writes:
> Having said that, there are times where you need to pass None as a 
> legitimate argument and not as a sentinel. 

I don't think it's worth trying to figure out which those times are.
The conclusion can be wrong, or can become wrong later because of
some faraway change in the code.  I prefer using the bulletproof
method from the beginning, whether it is needed or not.