Kata

I agree. There is also already a kata on Euler's method. Maybe enforce a more efficient algorithm (and defo make it non-analytical)?

I would suggest to make kata with differential equation, that does not have analytical solution (i.e. riccati system) and enforce large difference between y(0) and y(T). Furthermore, as Unnamed suggested, you should disable some Python modules, that allow user to cheat the kata.

Now I've found the kata that concerns the Euler's method. I've been planning to create the whole series about solving systems of differential equations and I wanted to start off with something easy. Maybe I will transform the task into the system of two equations or, as rge123 suggested, I will enforce improved Euler's method.

Answering dolamroth suggestions:

1. I don't quite follow, I need to think this through
2. I will change the task to be more specific

Now I am aware that I should disable some functions but I can not figure it out. How to block a function? I know it may be a silly question but I've been trying to find this out and no success.

About forbidding modules: Here is old code from one of my katas, it would give you the general idea. You need to include this code in Preloaded section. (note, that test is import codewars_test as test)

import random

toForbid  = ['importlib', '_frozen_importlib', 'os', 'sys', 'builtins',
             '_frozen_importlib', '_frozen_importlib_external', '_imp',
             'gc', 'json', 'requests', 'subprocess']

def module_forbidder(*forbid):   
    from functools import wraps
    import re, sys
    original      = __import__
    checker       = 'extract.hlsidhgfoisHDE67678EFG2Sdyftsrtstfh'
    modulesToKeep = ('random',)
    keptModules   = tuple(__import__(name) for name in modulesToKeep)
    toForbid.extend(modulesToKeep)
    for name in modulesToKeep + ('sys',):
        del sys.modules[name]
    @wraps(__import__)
    def DontDoThis(*a,**k):
        if a[0] == checker: return keptModules
        for name in forbid:
            if re.search(r'\b{}\b'.format(name), a[0]):
                test.fail("Don't import {} or a module that depends on it.".format(name))
                raise Exception("Don't do this...")
        try:    return original(*a,**k)
        except: pass         
    return DontDoThis
array_to_delete = tuple(('functools', 'itertools', 'operator', '_operator'))
toForbid.extend(array_to_delete)
__builtins__['__import__'] = module_forbidder(*toForbid)

for func in 'eval exec open'.split():  __builtins__[func] = None

del module_forbidder, toForbid, func