'I am very {dfghjk} good boy.'

'I am very good boy.'

In [120]: import re

In [121]: s
Out[121]: '{Am} I am very {bad} good {girl} boy.'

In [122]: re.sub(r'{[^}]*}', '', s)
Out[122]: ' I am very  good  boy.'

In [125]: re.sub('s+', ' ', re.sub(r'{[^}]*}', '', s)).strip()
Out[125]: 'I am very good boy.'

def replace_from_kwargs(arg: str, **kwargs) -> str:
    try:
        return arg.format(**kwargs)
    except KeyError as ex:
        kwargs.update({}.fromkeys(ex.args, ''))
        return replace_from_kwargs(arg, **kwargs)

A = 'I am very {dfghjk} good boy. {qw1e}'
print(replace_from_kwargs(A))