10.4 Applying partial arguments with partial()

The partial() function leads to something called a partial application. A partially applied function is a new function built from an old function and a subset of the required argument values. It is closely related to the concept of currying. Much of the theoretical background is not relevant here, since currying doesn’t apply directly to the way Python functions are implemented. The concept, however, can lead us to some handy simplifications.

We can look at trivial examples as follows:

>>> exp2 = partial(pow, 2)
>>> exp2(12)
4096
>>> exp2(17)-1
131071

We’ve created the function exp2(y), which is the pow(2, y) function. The partial() function binds the first positional parameter to the pow() function. When we evaluate the newly created exp2() function, we get values computed from the argument bound by the partial() function, plus the additional argument provided to the exp2() function.

The bindings...