lambda function not accepting mapping regulation via input (Python)

Question

How can I make a function in the lambda form accept a mapping regulation via input instead of explicitly stating it in the function?

Here is my code, I am trying to create a program for nummerical integration.

while True:

 fx=input("Enter a function: ")
 a=int(input("Choose lower integration limit: "))
 b=int(input("Choose upper integration limit: "))
 delta=float(input("Choose delta x: "))

 step=int(1/delta)

 interval=list(range((a*step),(b*step)))
 f= lambda x: (x**2)*delta

Now I want to substitute this part (x**2) for an arbitray polynomial via the input fx

 result=map(f,interval)
 print(sum(list(result))*(delta**2))


continue

if i try substituting (x**2) for fx it will produce this error:

Traceback (most recent call last):
  File "C:\Users\Christian\Desktop\Python-Programme\Nummerische         Integration.py", line 13, in <module>
    print(sum(list(result))*(delta**2))
  File "C:\Users\Christian\Desktop\Python-Programme\Nummerische    Integration.py", line 11, in <lambda>
    f= lambda x: fx*delta
TypeError: can't multiply sequence by non-int of type 'float'

*I am fully aware that this is probably not an optimal program for nummerical integration, the reason why im building this is just to exercise my programming skills while making programs that I still could theoreticaly use.

Answer 1

Disregarding of the question if this makes sense, the error comes from a type mismatch:

When you get the input from fx=input("Enter a function: ") the variable fx will be of type str. Try print(type(fx)).

When you then perform fx*delta you basically try to multiply a string with a numerical value, which does not make sense. Thus your Error TypeError: can't multiply sequence by non-int of type 'float'.

A quick solution would be

while True:
    n=int(input("Enter degree of polynomial: "))
    print(type(fx))
    a=int(input("Choose lower integration limit: "))
    b=int(input("Choose upper integration limit: "))
    delta=float(input("Choose delta x: "))
    step=int(1/delta)
    interval=list(range((a*step),(b*step)))
    f= lambda x: (x**n)*delta
    result=map(f,interval)
    print(sum(list(result))*(delta**2))
    continue

An advanced solution would need a way to parse your string input into a lambda function, which I think is not that easy.