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How do you use functools.partial to create a new function with some arguments pre-filled?

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Answer

functools.partial(func, *args, **kwargs) returns a NEW callable that, when invoked, calls the ORIGINAL function with the pre-filled arguments PLUS whatever additional arguments are passed at call time — a clean, explicit alternative to writing a small wrapper lambda for the same purpose.
from functools import partial

def power(base, exponent):
    return base ** exponent

square = partial(power, exponent=2)  # 'exponent' pre-filled
print(square(5))  # 25, equivalent to power(5, exponent=2)
Real-world example Creating a specialized, pre-configured version of a generic function, like a square() function derived from a general power() function.

Common follow-ups: How does functools.partial differ from simply writing an equivalent lambda that calls the original function?

functools & Functional Programming Tools
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