Partial Function Application -- Advantages over normal function?

[Kurian Thayil]

Hi,

I am a newbie in python and would like to learn GUI programming. I would like
to know what exactly is Partial Function Applicaton (functool.partial())? Or
how is it advantageous compared to normal functions? Or is there any
advantange? Thanks in advance.

Regards,
Kurian Thayil.

 

[Steven D'Aprano]

Hi,

I am a newbie in python and would like to learn GUI programming. I would
like to know what exactly is Partial Function Applicaton
(functool.partial())? Or how is it advantageous compared to normal
functions? Or is there any advantange? Thanks in advance.

It is mostly for functional programming style.

But one lucky side-effect of the implementation is that partial functions
*may* sometimes be faster than the alternative written in pure Python,
provided the original function is written in C:


from functools import partial
from operator import add

def add_one(x):
return add(1, x) # Like 1+x

add_two = partial(add, 2)

from timeit import Timer
setup = "from __main__ import add_one, add_two"
t1 = Timer("add_one(42)", setup)
t2 = Timer("add_two(42)", setup)



And in action:
0.3557558059692383

So in this example, the partial function is about twice as fast as the one
written in Python.

This does not necessarily apply for all functions, but it sometimes is
useful.

 

[woooee]

Partial can be used in a GUI program, like Tkinter, to send arguments
to functions. There are other ways to do that as well as using
partial. The following program uses partial to send the color to the
change_buttons function.
from Tkinter import *
from functools import partial

class App:
def __init__(self, parent):
self.my_parent = parent
self.my_parent.geometry("200x100+10+10")

self.R = list()
for ctr, color in enumerate(("Red", "Blue", "Green")):
btn = Radiobutton(self.my_parent, text=color, value=ctr+1,
command=partial(self.change_buttons, color))
btn.grid(row = 2, column = ctr+1)
btn.deselect()
self.R.append(btn)
self.R[0].select()
self.change_buttons("Red")


def change_buttons(self, color):
self.my_parent.configure(bg=color)
for btn in self.R:
btn.configure(bg=color)

if __name__ == "__main__":
root = Tk()
root.title ("Color Option")
app = App(root)
root.mainloop()

 

[Terry Reedy]

Partial can be used in a GUI program, like Tkinter, to send arguments
to functions. There are other ways to do that as well as using
partial. The following program uses partial to send the color to the
change_buttons function.
from Tkinter import *
from functools import partial

class App:
def __init__(self, parent):
self.my_parent = parent
self.my_parent.geometry("200x100+10+10")

self.R = list()
for ctr, color in enumerate(("Red", "Blue", "Green")):
btn = Radiobutton(self.my_parent, text=color, value=ctr+1,
command=partial(self.change_buttons, color))
btn.grid(row = 2, column = ctr+1)

This is a nice illustration. For future reference: enumerate now takes a
start value as second parameter. Given as 1, you do not need to remember
to add 1 for each usage.

for ctr, color in enumerate(("Red", "Blue", "Green"),1):
btn = Radiobutton(self.my_parent, text=color, value=ctr,
command=partial(self.change_buttons, color))
btn.grid(row = 2, column = ctr)

btn.deselect()
self.R.append(btn)
self.R[0].select()
self.change_buttons("Red")

def change_buttons(self, color):
self.my_parent.configure(bg=color)
for btn in self.R:
btn.configure(bg=color)

if __name__ == "__main__":
root = Tk()
root.title ("Color Option")
app = App(root)
root.mainloop()