Partial Functions

functools.partial pre-fills arguments to make a more specific callable.

Without partial, callers repeat the same fixed argument every time they want the specialized behavior.

Source

def apply_tax(rate, amount):
    return round(amount * (1 + rate), 2)

print(apply_tax(0.2, 50))

Output

60.0

f(a, b, c)partial(f, 1)g(b, c)functools.partial(f, 1) pre-fills a=1, returning a thinner callable g(b, c) that only needs the rest.

partial stores that fixed argument and returns a callable shaped for the remaining arguments.

Source

from functools import partial

vat = partial(apply_tax, 0.2)
service_tax = partial(apply_tax, rate=0.1)

print(vat(50))
print(service_tax(amount=80))

Output

60.0
88.0

Partial objects expose the function and stored arguments, which is helpful when debugging callback wiring.

Source

print(vat.func.__name__)
print(vat.args)

Output

apply_tax
(0.2,)

Notes

partial adapts a callable by pre-filling arguments.
The resulting object can be passed anywhere a callable with the remaining parameters is expected.
Use a regular function when the adapter needs more logic than argument binding.

Run the complete example

60.0
60.0
88.0
apply_tax
(0.2,)

Execution time appears here after you run the example.

Web Proxy Viewer | New URL | Original Page