how to avoid checking the same condition repeatedly ?

[Peter Cacioppi]

Chris said :
"Want some examples of what costs no clarity to reimplement in another language? Check out the Python standard library. Some of that is implemented in C (in CPython) and some in Python, and you can't tell and needn't care which."

To ME (a consumer of the CPython library) there is zero cost to clarity.

To the angels that maintain/develop this library and need to go inside the black box regularly .... there is a non-zero cost to clarity.

Right? 

(I'd rather run the risk of stating the obvious than missing something clever, that's why I keep hitting this sessile equine).