创建一个能够根据给定参数生成函数对象（在这种情况下为分段函数）的脚本

Question

I was wondering what is the best way to do the following. Consider a piecewise function which takes on constant values for different ranges. For example: from t = 0 to t = 2 , x = 3 and from t = 2 to t = 4, x = 1. I define a piecewise function by the following parameters:

• list of x, eg [3,3,1,1,1]

or

• two lists which generate a list of x. The example above is generated by [3,1] (values of x) and [2,3] (how often they are repeated).

From this, I want the script to create the following function, using the example above:

def function(x):
    if 0 <= x < 2:
        return 3
    if 2 <= x <= 4:
        return 1

Thus I need some method that will take in either the list of x values or the list of x and how often they are repeated to create a function of x:

def function(x)
    if bound1 <= x < bound2:
        return x1
    if bound2 <= x < bound3: 
        return x2
    if bound3 <= x < bound4:
        return x3

    ...

    if bound_n-1 <= x < bound_n:
        return x_n

I've been reading on classes and function wrapping but I'm still slightly unsure as to what would be the best solution for this problem.

Thanks

Answer 1

Maybe you should look at bisect.bisect_right function ( official doc ):

from bisect import bisect_right
from functools import partial

# <0, 2) -> 3
# <2, 4) -> 1
# <4, 6) -> 99
bounds          = [0, 2, 4, 6]
return_values   = [3, 1, 99]

def fn(val, bounds, return_values):
    i = bisect_right(bounds, val) - 1
    return return_values[i] if i < len(return_values) else None

# function(x)
function = partial(fn, bounds=bounds, return_values=return_values)

print(function(0))
print(function(1))
print(function(2))
print(function(3))
print(function(4))
print(function(5))
print(function(6))

Prints:

3
3
1
1
99
99
None

Edit: Updated answer to call the function() just with one parameter.