How to use Python decorators to check function arguments?

Question

I would like to define some generic decorators to check arguments before calling some functions.

Something like:

@checkArguments(types = [\'int\', \'         


        

Answer 1

To enforce string arguments to a parser that would throw cryptic errors when provided with non-string input, I wrote the following, which tries to avoid allocation and function calls:

from functools import wraps

def argtype(**decls):
    """Decorator to check argument types.

    Usage:

    @argtype(name=str, text=str)
    def parse_rule(name, text): ...
    """

    def decorator(func):
        code = func.func_code
        fname = func.func_name
        names = code.co_varnames[:code.co_argcount]

        @wraps(func)
        def decorated(*args,**kwargs):
            for argname, argtype in decls.iteritems():
                try:
                    argval = args[names.index(argname)]
                except ValueError:
                    argval = kwargs.get(argname)
                if argval is None:
                    raise TypeError("%s(...): arg '%s' is null"
                                    % (fname, argname))
                if not isinstance(argval, argtype):
                    raise TypeError("%s(...): arg '%s': type is %s, must be %s"
                                    % (fname, argname, type(argval), argtype))
            return func(*args,**kwargs)
        return decorated

    return decorator