Python はメソッドのオーバーロードをどのように処理しますか?

<code class="python">class A:
    def stackoverflow(self, i='some_default_value'):
        print('only method')

ob = A()
ob.stackoverflow(2)  # prints 'only method'
ob.stackoverflow()   # prints 'only method' with 'some_default_value'</code>

<code class="python">from functools import singledispatch

@singledispatch
def fun(arg, verbose=False):
    print(arg)

@fun.register(int)
def _(arg, verbose=False):
    print(arg)

@fun.register(list)
def _(arg, verbose=False):
    for i, elem in enumerate(arg):
        print(i, elem)</code>