user input string to function

[Chris Angelico]

On Tue, Dec 26, 2017 at 1:48 AM, Nico Vogeli <nicco.9537 at gmail.com> wrote:
> Am Montag, 25. Dezember 2017 14:51:21 UTC+1 schrieb Chris Angelico:
>> On Tue, Dec 26, 2017 at 12:36 AM, Nico Vogeli <nicco.9537 at gmail.com> wrote:
>> > Hi everybody. First ad foremost, happy Christmas!
>>
>> Same to you!
>>
>> > I want to let the use input a function (like x**2) and parse it after that through code (for my numeric class)
>> >
>> > def newton(x0, s, s2, tol, n = 20000):
>> >     '''
>> >     Näherung zur lösung einer Gleichung mit dem Newton-Verfahren
>> >     x0 = Startwert
>> >     f = zu lösende Funktion
>> >     fx = Ableitung der Funktion
>> >
>> >     '''
>> >     def f(a):
>> >         y = s
>> >         return y
>> >
>> >     def fx(a):
>> >         y = s2
>> >         return y
>>
>>
>> > newton(2, 3*x**2, 6*x, 0.1, 2)
>> >
>> > I notice that the x is not converted to an integer, because of the x = symplos('x')
>> > But I don't know how I could possibli change the code to work...
>>
>> The easiest way is to pass a *function* to newton(). It'd look like this:
>>
>> def newton(x0, f, fx, tol, n=20000):
>>     ... as before, but without the nested functions
>>
>> newton(2, lambda x: 3*x**2, lambda x: 6*x, 0.1, 2)
>>
>> At least, I think that's how you're doing things. Inside the nested
>> functions, you use 'a', but outside, you use 'x'. Are those
>> representing the same concept? If so, the lambda functions given here
>> will have the same effect.
>>
>> Hope that helps!
>>
>> ChrisA
>
> Hi Chris
>
> Thanks very much for your quick response!
> I was in a bit of a rush, so I confused the variables (don't worry, I just messed arround to try different things, the original code was al tidy with the variable).
>
> I tried your input, but now I get another error:
>
>
>   File "C:/Users/Nicco ZHAW/Desktop/Test GUI/Test Projekt.py", line 42, in newton
>     b = x - f(x)/fx(x)
>
> TypeError: unsupported operand type(s) for /: 'function' and 'function'
>
> This did not occure befor I tried to implement the user input..

Did you remove the nested functions? The lambda functions completely
replace your "def f(a)" and "def fx(a)" functions.

ChrisA