user input string to function

[Chris Angelico]

On Tue, Dec 26, 2017 at 2:04 AM, Nico Vogeli <nicco.9537 at gmail.com> wrote:
> Am Montag, 25. Dezember 2017 15:58:26 UTC+1 schrieb 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
>
> I am so so sorry!! I just did not know what you meant by sested functions.. :P

No need to apologize! That's why we have two-directional communication
- I can ask you to clarify, you can ask me to clarify, and we get to a
solution.

The concept of passing functions around does take some getting used
to, so there's no shame in not instantly understanding it.

> Thank you so much for helping me! You're great!
>
> Cheers and all the best!

My pleasure! Have yourself an awesome holiday season.

ChrisA