94 lines
2.0 KiB
Markdown
94 lines
2.0 KiB
Markdown
# Exercise 4.2 - Solution
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Here is the validator code in its entirety:
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```python
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class Validator:
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@classmethod
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def check(cls, value):
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return value
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class Typed(Validator):
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expected_type = object
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@classmethod
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def check(cls, value):
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if not isinstance(value, cls.expected_type):
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raise TypeError(f'Expected {cls.expected_type}')
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return super().check(value)
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class Integer(Typed):
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expected_type = int
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class Float(Typed):
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expected_type = float
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class String(Typed):
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expected_type = str
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class Positive(Validator):
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@classmethod
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def check(cls, value):
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if value < 0:
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raise ValueError('Must be >= 0')
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return super().check(value)
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class NonEmpty(Validator):
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@classmethod
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def check(cls, value):
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if len(value) == 0:
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raise ValueError('Must be non-empty')
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return super().check(value)
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class PositiveInteger(Integer, Positive):
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pass
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class PositiveFloat(Float, Positive):
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pass
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class NonEmptyString(String, NonEmpty):
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pass
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```
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## (c) Using the validators
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```python
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# validate.py
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...
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if __name__ == '__main__':
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class Stock:
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__slots__ = ('name', '_shares', '_price')
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def __init__(self, name, shares, price):
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self.name = name
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self.shares = shares
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self.price = price
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def __repr__(self):
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return f'Stock({self.name!r}, {self.shares!r}, {self.price!r})'
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@property
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def shares(self):
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return self._shares
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@shares.setter
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def shares(self, value):
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self._shares = PositiveInteger.check(value)
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@property
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def price(self):
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return self._price
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@price.setter
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def price(self, value):
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self._price = PositiveFloat.check(value)
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@property
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def cost(self):
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return self.shares * self.price
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def sell(self, nshares):
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self.shares -= nshares
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```
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[Back](ex4_2.md)
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