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Simple type checked objects in Python
#!/usr/bin/env python
from type_checked_entities import entity_factory
Giraffe = entity_factory( # let's define what is a giraffe!
"giraffe",
name=str, # my name is a string
age=float, # my age is an int
eats=object, # I eat pretty much everything.
)
Giraffe.say_hi = lambda self: "the giraffe {} says hi!".format(self.name) # example property of a giraffe
Grass = entity_factory(
"grass",
color='green'
)
grass = Grass()
giraffe_1 = Giraffe(
name="Gira",
age=21,
eats=grass
)
giraffe_2 = Giraffe()
print giraffe_1.say_hi() # the giraffe Gira says hi!
try:
print giraffe_2.say_hi() # explicitly fails, giraffe_2.name needed for the method is still undefined
except ValueError as error:
print error
giraffe_2.name = "rhino" # whoa, didn't see this coming
giraffe_2.say_hi()
try:
giraffe_2.age = 11.5
except TypeError as error: # 11.5 is not an valid int age
print error
giraffe_2.age = 11
#!/usr/bin/env python
__author__ = "Luca Giacomel"
__license__ = "Public Domain"
def generate_setter(field):
def setter(self, value):
field = setter.__name__[4:]
if isinstance(value, self.enforced_types[field]):
setattr(self, "_%s" % field, value)
else:
raise TypeError("%s object cannot have property %s with value \"%s\" (type: %s - it must be %s)" % (
self.__class__,
field,
value,
type(value),
self.enforced_types[field]))
setter.__name__ = "set_%s" % field
return setter
def generate_getter(field):
def getter(self):
field = getter.__name__[4:]
if not hasattr(self, "_%s" % field):
raise ValueError("property %s of instance %s of object %s is undefined" %
(field, self.__repr__(), self.__class__))
return getattr(self, "_%s" % field)
getter.__name__ = "set_%s" % field
return getter
def entity_factory(entity_type, **kwargs):
props = dict()
props['enforced_types'] = kwargs
for obj, _ in kwargs.items():
props[obj] = property(generate_getter(obj), generate_setter(obj))
def __init__(self, **kwargs):
for attr, tpe in kwargs.items():
if attr in props['enforced_types'] and isinstance(attr, props['enforced_types'][attr]):
setattr(self, "_%s" % attr, tpe)
props['__init__'] = __init__
cls = type(
entity_type,
(object,),
props
)
return cls
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