This decorator can be used to cast argument types automatically, using a pre-specified list of types, when a function is called.
Python, 28 lines
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Copy to clipboard1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | class ConvertArgumentTypes(object):
"""Converts function arguments to specified types."""
def __init__(self,*args, **kw):
self.args = args
self.kw = kw
def __call__(self, f):
def func(*args, **kw):
nargs = [x[0](x[1]) for x in zip(self.args, args)]
invalidkw = [x for x in kw if x not in self.kw]
if len(invalidkw) > 0:
raise TypeError, f.func_name + "() got an unexpected keyword argument '%s'" % invalidkw[0]
kw = dict([(x,self.kw[x](kw[x])) for x in kw])
v = f(*nargs, **kw)
return v
return func
#keyword arguments are handled normally.
@ConvertArgumentTypes(int, float, c=int, d=str)
def z(a,b,c=0,d=""):
return a + b, (c,d)
@ConvertArgumentTypes(int, int)
def y(p,q):
return p + q
print y("1","2")
print z(1,2,c=34,d=56)
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It's not incredibly useful, but is handy in a few corner cases where you need to guarantee that your function arguments will be of a certain type.
It could also be used to apply functions automatically to arguments as a function is called. This could be useful in a data validation scenario, encouraging very loose coupling between validation functions and application logic.
Similar recipes are: http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/325917 http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/355638
Updated: now handles keyword arguments.
Tags: shortcuts
