如何在 Python 中获取数学函数作为用户的输入并在循环中使用它

Question

I used f = lambda x: input() to get a mathematical function as the user's input. I put this in a for loop, but input is requested in every iteration. How do I store the function in a variable only once and use it in the loop?

Here's my code:

from math import cos, sin, pow, e

n = int(input('Number of elements in partition: '))
print('The range is set at ...... ')
minimum = int(input('Minimum: '))
maximum = int(input('Maximum: '))
f = lambda x: eval(input('Enter a funtion: '))

fraction = (maximum - minimum) / (n-1)

UpperSum = 0
LowerSum = 0

for i in range(1, n):
    UpperSum = UpperSum + fraction * f(fraction * i)
    LowerSum = LowerSum + fraction * f(fraction * (i - 1))

Answer 1

You've specifically made function input part of the function itself:

f = lambda x: eval(input('Enter a funtion: '))

As the old line goes, "If it hurts when you do that, then don't do that!" Input the function only once:

func_text = input('Enter a function: ')
func_eval = eval(func_text)
f = lambda x: func_eval

I broke it down one extra step. The point, though, is to read the input, evaluate it, and then make only that evaluation the function you call.