[FIXED] Python Argument Binders

Issue

How can I bind arguments to a Python function so that I can call it later without arguments (or with fewer additional arguments)?

For example:

def add(x, y):
    return x + y

add_5 = magic_function(add, 5)
assert add_5(3) == 8

What is the magic_function I need here?

---

_{It often happens with frameworks and libraries that people accidentally call a function immediately when trying to give arguments to a callback: for example on_event(action(foo)). The solution is to bind foo as an argument to action, using one of the techniques described here.}

_{Some specific examples: Why is my Button's command executed immediately when I create the Button, and not when I click it?, thread starts running before calling Thread.start.}

Solution

functools.partial returns a callable wrapping a function with some or all of the arguments frozen.

import sys
import functools

print_hello = functools.partial(sys.stdout.write, "Hello world\n")

print_hello()

Hello world

The above usage is equivalent to the following lambda.

print_hello = lambda *a, **kw: sys.stdout.write("Hello world\n", *a, **kw)

Answered By - Jeremy