Python : addition of lambda defined functions

Question

I am wondering if there is any way of adding to lambda functions at the function level.

import numpy as np

f = lambda x: np.sin(5*x)+3
g = lambda x: np.cos(3*x)**2+1

x = np.linspace(-3.14,3.14,1000)
h = f+g  % is there any way to create this ?
h_of_x = h(x)

This would be very helpful.

Sure would be cute if function addition could be defined by providing them with an __add__ attribute: a.__add__ = lambda self, b: return lambda *x: self(*x) + b(*x). But python doesn't seem to care if functions have an __add__ method :-) — alexis
– alexis, Commented May 5, 2015 at 18:49
Ok, it doesn't work OOTB, but as @shx2's answer shows, there's a library for it! Neat. — alexis
– alexis, Commented May 5, 2015 at 18:52
@alexis, Yes but I like to refrain from mixing sympy with numpy as it gives weird error messages when you manipulate functions (32 dimensions limit) — Mathusalem
– Mathusalem, Commented May 5, 2015 at 18:53

shx2 · Accepted Answer · 2015-05-05 18:48:39Z

4

If you're looking for symbolic mathematics, use sympy.

from sympy import *
x = symbols("x")
f = sin(5*x)+3
g = cos(3*x)**2+1
h = f + g

answered May 5, 2015 at 18:48

shx2

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Hackaholic · Accepted Answer · 2015-05-05 18:40:23Z

3

May be this

h = lambda x: f(x)+g(x)

answered May 5, 2015 at 18:40

Hackaholic

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Comments

JuniorCompressor · Accepted Answer · 2015-05-05 18:59:23Z

2

You can create a function plus that takes two functions as input and return their sum:

def plus(f, g):
    def h(x):
        return f(x) + g(x)
    return h

h = plus(lambda x: x * x, lambda x: x ** 3)

Example:

>>> h(2)
12

Defining plus can have advantages, like:

>>> f = lambda x: x * 2
>>> h = reduce(plus, [f, f, f, f]) # or h = reduce(plus, [f] * 4)
>>> h(2)
16

edited May 5, 2015 at 18:59

answered May 5, 2015 at 18:49

JuniorCompressor

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