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* gh-68163: Correct conversion of Rational instances to float Also document that numerator/denominator properties are instances of Integral. Co-authored-by: Mark Dickinson <dickinsm@gmail.com>
419 lines
11 KiB
Python
419 lines
11 KiB
Python
# Copyright 2007 Google, Inc. All Rights Reserved.
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# Licensed to PSF under a Contributor Agreement.
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"""Abstract Base Classes (ABCs) for numbers, according to PEP 3141.
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TODO: Fill out more detailed documentation on the operators."""
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############ Maintenance notes #########################################
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#
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# ABCs are different from other standard library modules in that they
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# specify compliance tests. In general, once an ABC has been published,
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# new methods (either abstract or concrete) cannot be added.
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#
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# Though classes that inherit from an ABC would automatically receive a
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# new mixin method, registered classes would become non-compliant and
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# violate the contract promised by ``isinstance(someobj, SomeABC)``.
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#
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# Though irritating, the correct procedure for adding new abstract or
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# mixin methods is to create a new ABC as a subclass of the previous
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# ABC.
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#
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# Because they are so hard to change, new ABCs should have their APIs
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# carefully thought through prior to publication.
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#
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# Since ABCMeta only checks for the presence of methods, it is possible
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# to alter the signature of a method by adding optional arguments
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# or changing parameter names. This is still a bit dubious but at
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# least it won't cause isinstance() to return an incorrect result.
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#
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#
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#######################################################################
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from abc import ABCMeta, abstractmethod
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__all__ = ["Number", "Complex", "Real", "Rational", "Integral"]
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class Number(metaclass=ABCMeta):
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"""All numbers inherit from this class.
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If you just want to check if an argument x is a number, without
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caring what kind, use isinstance(x, Number).
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"""
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__slots__ = ()
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# Concrete numeric types must provide their own hash implementation
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__hash__ = None
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## Notes on Decimal
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## ----------------
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## Decimal has all of the methods specified by the Real abc, but it should
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## not be registered as a Real because decimals do not interoperate with
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## binary floats (i.e. Decimal('3.14') + 2.71828 is undefined). But,
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## abstract reals are expected to interoperate (i.e. R1 + R2 should be
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## expected to work if R1 and R2 are both Reals).
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class Complex(Number):
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"""Complex defines the operations that work on the builtin complex type.
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In short, those are: a conversion to complex, .real, .imag, +, -,
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*, /, **, abs(), .conjugate, ==, and !=.
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If it is given heterogeneous arguments, and doesn't have special
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knowledge about them, it should fall back to the builtin complex
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type as described below.
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"""
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__slots__ = ()
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@abstractmethod
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def __complex__(self):
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"""Return a builtin complex instance. Called for complex(self)."""
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def __bool__(self):
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"""True if self != 0. Called for bool(self)."""
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return self != 0
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@property
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@abstractmethod
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def real(self):
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"""Retrieve the real component of this number.
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This should subclass Real.
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"""
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raise NotImplementedError
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@property
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@abstractmethod
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def imag(self):
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"""Retrieve the imaginary component of this number.
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This should subclass Real.
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"""
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raise NotImplementedError
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@abstractmethod
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def __add__(self, other):
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"""self + other"""
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raise NotImplementedError
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@abstractmethod
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def __radd__(self, other):
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"""other + self"""
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raise NotImplementedError
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@abstractmethod
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def __neg__(self):
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"""-self"""
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raise NotImplementedError
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@abstractmethod
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def __pos__(self):
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"""+self"""
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raise NotImplementedError
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def __sub__(self, other):
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"""self - other"""
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return self + -other
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def __rsub__(self, other):
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"""other - self"""
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return -self + other
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@abstractmethod
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def __mul__(self, other):
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"""self * other"""
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raise NotImplementedError
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@abstractmethod
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def __rmul__(self, other):
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"""other * self"""
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raise NotImplementedError
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@abstractmethod
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def __truediv__(self, other):
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"""self / other: Should promote to float when necessary."""
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raise NotImplementedError
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@abstractmethod
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def __rtruediv__(self, other):
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"""other / self"""
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raise NotImplementedError
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@abstractmethod
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def __pow__(self, exponent):
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"""self ** exponent; should promote to float or complex when necessary."""
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raise NotImplementedError
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@abstractmethod
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def __rpow__(self, base):
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"""base ** self"""
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raise NotImplementedError
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@abstractmethod
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def __abs__(self):
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"""Returns the Real distance from 0. Called for abs(self)."""
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raise NotImplementedError
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@abstractmethod
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def conjugate(self):
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"""(x+y*i).conjugate() returns (x-y*i)."""
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raise NotImplementedError
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@abstractmethod
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def __eq__(self, other):
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"""self == other"""
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raise NotImplementedError
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Complex.register(complex)
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class Real(Complex):
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"""To Complex, Real adds the operations that work on real numbers.
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In short, those are: a conversion to float, trunc(), divmod,
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%, <, <=, >, and >=.
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Real also provides defaults for the derived operations.
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"""
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__slots__ = ()
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@abstractmethod
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def __float__(self):
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"""Any Real can be converted to a native float object.
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Called for float(self)."""
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raise NotImplementedError
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@abstractmethod
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def __trunc__(self):
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"""trunc(self): Truncates self to an Integral.
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Returns an Integral i such that:
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* i > 0 iff self > 0;
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* abs(i) <= abs(self);
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* for any Integral j satisfying the first two conditions,
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abs(i) >= abs(j) [i.e. i has "maximal" abs among those].
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i.e. "truncate towards 0".
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"""
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raise NotImplementedError
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@abstractmethod
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def __floor__(self):
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"""Finds the greatest Integral <= self."""
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raise NotImplementedError
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@abstractmethod
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def __ceil__(self):
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"""Finds the least Integral >= self."""
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raise NotImplementedError
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@abstractmethod
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def __round__(self, ndigits=None):
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"""Rounds self to ndigits decimal places, defaulting to 0.
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If ndigits is omitted or None, returns an Integral, otherwise
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returns a Real. Rounds half toward even.
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"""
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raise NotImplementedError
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def __divmod__(self, other):
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"""divmod(self, other): The pair (self // other, self % other).
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Sometimes this can be computed faster than the pair of
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operations.
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"""
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return (self // other, self % other)
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def __rdivmod__(self, other):
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"""divmod(other, self): The pair (other // self, other % self).
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Sometimes this can be computed faster than the pair of
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operations.
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"""
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return (other // self, other % self)
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@abstractmethod
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def __floordiv__(self, other):
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"""self // other: The floor() of self/other."""
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raise NotImplementedError
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@abstractmethod
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def __rfloordiv__(self, other):
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"""other // self: The floor() of other/self."""
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raise NotImplementedError
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@abstractmethod
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def __mod__(self, other):
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"""self % other"""
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raise NotImplementedError
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@abstractmethod
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def __rmod__(self, other):
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"""other % self"""
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raise NotImplementedError
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@abstractmethod
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def __lt__(self, other):
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"""self < other
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< on Reals defines a total ordering, except perhaps for NaN."""
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raise NotImplementedError
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@abstractmethod
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def __le__(self, other):
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"""self <= other"""
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raise NotImplementedError
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# Concrete implementations of Complex abstract methods.
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def __complex__(self):
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"""complex(self) == complex(float(self), 0)"""
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return complex(float(self))
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@property
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def real(self):
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"""Real numbers are their real component."""
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return +self
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@property
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def imag(self):
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"""Real numbers have no imaginary component."""
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return 0
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def conjugate(self):
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"""Conjugate is a no-op for Reals."""
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return +self
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Real.register(float)
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class Rational(Real):
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""".numerator and .denominator should be in lowest terms."""
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__slots__ = ()
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@property
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@abstractmethod
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def numerator(self):
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raise NotImplementedError
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@property
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@abstractmethod
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def denominator(self):
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raise NotImplementedError
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# Concrete implementation of Real's conversion to float.
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def __float__(self):
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"""float(self) = self.numerator / self.denominator
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It's important that this conversion use the integer's "true"
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division rather than casting one side to float before dividing
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so that ratios of huge integers convert without overflowing.
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"""
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return int(self.numerator) / int(self.denominator)
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class Integral(Rational):
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"""Integral adds methods that work on integral numbers.
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In short, these are conversion to int, pow with modulus, and the
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bit-string operations.
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"""
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__slots__ = ()
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@abstractmethod
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def __int__(self):
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"""int(self)"""
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raise NotImplementedError
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def __index__(self):
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"""Called whenever an index is needed, such as in slicing"""
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return int(self)
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@abstractmethod
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def __pow__(self, exponent, modulus=None):
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"""self ** exponent % modulus, but maybe faster.
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Accept the modulus argument if you want to support the
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3-argument version of pow(). Raise a TypeError if exponent < 0
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or any argument isn't Integral. Otherwise, just implement the
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2-argument version described in Complex.
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"""
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raise NotImplementedError
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@abstractmethod
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def __lshift__(self, other):
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"""self << other"""
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raise NotImplementedError
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@abstractmethod
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def __rlshift__(self, other):
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"""other << self"""
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raise NotImplementedError
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@abstractmethod
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def __rshift__(self, other):
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"""self >> other"""
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raise NotImplementedError
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@abstractmethod
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def __rrshift__(self, other):
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"""other >> self"""
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raise NotImplementedError
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@abstractmethod
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def __and__(self, other):
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"""self & other"""
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raise NotImplementedError
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@abstractmethod
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def __rand__(self, other):
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"""other & self"""
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raise NotImplementedError
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@abstractmethod
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def __xor__(self, other):
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"""self ^ other"""
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raise NotImplementedError
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@abstractmethod
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def __rxor__(self, other):
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"""other ^ self"""
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raise NotImplementedError
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@abstractmethod
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def __or__(self, other):
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"""self | other"""
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raise NotImplementedError
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@abstractmethod
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def __ror__(self, other):
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"""other | self"""
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raise NotImplementedError
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@abstractmethod
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def __invert__(self):
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"""~self"""
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raise NotImplementedError
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# Concrete implementations of Rational and Real abstract methods.
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def __float__(self):
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"""float(self) == float(int(self))"""
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return float(int(self))
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@property
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def numerator(self):
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"""Integers are their own numerators."""
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return +self
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@property
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def denominator(self):
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"""Integers have a denominator of 1."""
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return 1
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Integral.register(int)
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