Module and tests:
* Map conditions to related signals. * Make contexts unhashable. * Eliminate used "default" attribute in exception definitions. * Eliminate the _filterfunc in favor of a straight list. Docs: * Eliminate documented references to conditions that are not signals. * Eliminate parenthetical notes such as "1/0 --> Inf" which are no longer true with the new defaults.
This commit is contained in:
Raymond Hettinger
parent
563e449729
commit
5aa478badf
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@ -66,10 +66,8 @@ context for arithmetic, and signals.
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A decimal number is immutable. It has a sign, coefficient digits, and an
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exponent. To preserve significance, the coefficient digits do not truncate
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trailing zeroes. Decimals also include special values such as
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\constant{Infinity} (the result of \samp{1 / 0}), \constant{-Infinity},
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(the result of \samp{-1 / 0}), and \constant{NaN} (the result of
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\samp{0 / 0}). The standard also differentiates \constant{-0} from
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\constant{+0}.
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\constant{Infinity}, \constant{-Infinity}, and \constant{NaN}. The standard
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also differentiates \constant{-0} from \constant{+0}.
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The context for arithmetic is an environment specifying precision, rounding
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rules, limits on exponents, flags that indicate the results of operations,
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@ -82,9 +80,7 @@ Signals are types of information that arise during the course of a
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computation. Depending on the needs of the application, some signals may be
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ignored, considered as informational, or treated as exceptions. The signals in
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the decimal module are: \constant{Clamped}, \constant{InvalidOperation},
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\constant{ConversionSyntax}, \constant{DivisionByZero},
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\constant{DivisionImpossible}, \constant{DivisionUndefined},
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\constant{Inexact}, \constant{InvalidContext}, \constant{Rounded},
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\constant{DivisionByZero}, \constant{Inexact}, \constant{Rounded},
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\constant{Subnormal}, \constant{Overflow}, and \constant{Underflow}.
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For each signal there is a flag and a trap enabler. When a signal is
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@ -124,7 +120,7 @@ Context(prec=28, rounding=ROUND_HALF_EVEN, Emin=-999999999, Emax=999999999,
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Decimal instances can be constructed from integers, strings or tuples. To
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create a Decimal from a \class{float}, first convert it to a string. This
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serves as an explicit reminder of the details of the conversion (including
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representation error). Malformed strings signal \constant{ConversionSyntax}
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representation error). Malformed strings signal \constant{InvalidOperation}
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and return a special kind of Decimal called a \constant{NaN} which stands for
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``Not a number''. Positive and negative \constant{Infinity} is yet another
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special kind of Decimal.
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@ -274,10 +270,8 @@ To turn all the traps on or off all at once, use a loop. Also, the
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>>> getcontext().trap_enablers.update({Rounded:0, Inexact:0, Subnormal:0})
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>>> getcontext()
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Context(prec=9, rounding=ROUND_HALF_EVEN, Emin=-999999999, Emax=999999999,
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setflags=[], settraps=['Underflow', 'DecimalException', 'Clamped',
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'InvalidContext', 'InvalidOperation', 'ConversionSyntax',
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'DivisionByZero', 'DivisionImpossible', 'DivisionUndefined',
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'Overflow'])
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setflags=[], settraps=['Clamped', 'Underflow', 'InvalidOperation',
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'DivisionByZero', 'Overflow'])
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\end{verbatim}
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Applications typically set the context once at the beginning of a program
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@ -320,7 +314,7 @@ as other Python numeric types.
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The supplied \var{context} or, if not specified, the current context
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governs only the handling of malformed strings not conforming to the
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numeric string syntax. If the context traps \constant{ConversionSyntax},
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numeric string syntax. If the context traps \constant{InvalidOperation},
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an exception is raised; otherwise, the constructor returns a new Decimal
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with the value of \constant{NaN}.
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@ -730,13 +724,6 @@ exception is raised upon encountering the condition.
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reduced to fit by adding zeroes to the coefficient.
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\end{classdesc*}
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\begin{classdesc*}{ConversionSyntax}
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Trying to convert a malformed string such as: \code{Decimal('jump')}.
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Decimal converts only strings conforming to the numeric string
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syntax. If this signal is not trapped, returns \constant{NaN}.
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\end{classdesc*}
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\begin{classdesc*}{DecimalException}
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Base class for other signals.
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\end{classdesc*}
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@ -750,19 +737,6 @@ exception is raised upon encountering the condition.
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the inputs to the calculation.
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\end{classdesc*}
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\begin{classdesc*}{DivisionImpossible}
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Error performing a division operation. Caused when an intermediate result
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has more digits that the allowed by the current precision. If not trapped,
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returns \constant{NaN}.
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\end{classdesc*}
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\begin{classdesc*}{DivisionUndefined}
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This is a subclass of \class{DivisionByZero}.
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It occurs only in the context of division operations.
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\end{classdesc*}
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\begin{classdesc*}{Inexact}
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Indicates that rounding occurred and the result is not exact.
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@ -771,14 +745,6 @@ exception is raised upon encountering the condition.
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to detect when results are inexact.
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\end{classdesc*}
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\begin{classdesc*}{InvalidContext}
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This is a subclass of \class{InvalidOperation}.
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Indicates an error within the Context object such as an unknown
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rounding operation. If not trapped, returns \constant{NaN}.
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\end{classdesc*}
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\begin{classdesc*}{InvalidOperation}
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An invalid operation was performed.
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@ -809,7 +775,6 @@ exception is raised upon encountering the condition.
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\class{Rounded} are also signaled.
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\end{classdesc*}
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\begin{classdesc*}{Rounded}
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Rounding occurred though possibly no information was lost.
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@ -844,16 +809,11 @@ The following table summarizes the hierarchy of signals:
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Overflow(Inexact, Rounded)
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Underflow(Inexact, Rounded, Subnormal)
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InvalidOperation
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ConversionSyntax
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DivisionImpossible
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DivisionUndefined(InvalidOperation, exceptions.ZeroDivisionError)
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InvalidContext
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Rounded
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Subnormal
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\end{verbatim}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\subsection{Working with threads \label{decimal-threads}}
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@ -78,30 +78,30 @@ Traceback (most recent call last):
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...
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DivisionByZero: x / 0
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>>> c = Context()
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>>> c.trap_enablers[DivisionUndefined] = 0
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>>> print c.flags[DivisionUndefined]
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>>> c.trap_enablers[InvalidOperation] = 0
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>>> print c.flags[InvalidOperation]
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0
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>>> c.divide(Decimal(0), Decimal(0))
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Decimal("NaN")
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>>> c.trap_enablers[DivisionUndefined] = 1
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>>> print c.flags[DivisionUndefined]
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>>> c.trap_enablers[InvalidOperation] = 1
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>>> print c.flags[InvalidOperation]
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1
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>>> c.flags[DivisionUndefined] = 0
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>>> print c.flags[DivisionUndefined]
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>>> c.flags[InvalidOperation] = 0
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>>> print c.flags[InvalidOperation]
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0
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>>> print c.divide(Decimal(0), Decimal(0))
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Traceback (most recent call last):
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...
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...
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...
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DivisionUndefined: 0 / 0
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>>> print c.flags[DivisionUndefined]
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InvalidOperation: 0 / 0
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>>> print c.flags[InvalidOperation]
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1
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>>> c.flags[DivisionUndefined] = 0
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>>> c.trap_enablers[DivisionUndefined] = False
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>>> c.flags[InvalidOperation] = 0
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>>> c.trap_enablers[InvalidOperation] = 0
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>>> print c.divide(Decimal(0), Decimal(0))
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NaN
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>>> print c.flags[DivisionUndefined]
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>>> print c.flags[InvalidOperation]
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1
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>>>
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"""
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@ -152,7 +152,7 @@ ALWAYS_ROUND = 'ALWAYS_ROUND' # Every operation rounds at end.
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#Errors
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class DecimalException(ArithmeticError):
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"""Base exception class, defines default things.
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"""Base exception class.
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Used exceptions derive from this.
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If an exception derives from another exception besides this (such as
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@ -160,12 +160,6 @@ class DecimalException(ArithmeticError):
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called if the others are present. This isn't actually used for
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anything, though.
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Attributes:
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default -- If the context is basic, the trap_enablers are set to
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this by default. Extended contexts start out with them set
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to 0, regardless.
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handle -- Called when context._raise_error is called and the
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trap_enabler is set. First argument is self, second is the
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context. More arguments can be given, those being after
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@ -176,7 +170,6 @@ class DecimalException(ArithmeticError):
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To define a new exception, it should be sufficient to have it derive
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from DecimalException.
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"""
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default = 1
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def handle(self, context, *args):
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pass
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@ -288,7 +281,7 @@ class Inexact(DecimalException):
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The inexact signal may be tested (or trapped) to determine if a given
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operation (or sequence of operations) was inexact.
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"""
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default = 0
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pass
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class InvalidContext(InvalidOperation):
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"""Invalid context. Unknown rounding, for example.
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@ -315,7 +308,7 @@ class Rounded(DecimalException):
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The rounded signal may be tested (or trapped) to determine if a given
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operation (or sequence of operations) caused a loss of precision.
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"""
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default = 0
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pass
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class Subnormal(DecimalException):
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"""Exponent < Emin before rounding.
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@ -382,19 +375,15 @@ class Underflow(Inexact, Rounded, Subnormal):
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In all cases, Inexact, Rounded, and Subnormal will also be raised.
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"""
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# List of public traps and flags
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Signals = [Clamped, DivisionByZero, Inexact, Overflow, Rounded,
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Underflow, InvalidOperation, Subnormal]
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def _filterfunc(obj):
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"""Returns true if a subclass of DecimalException"""
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try:
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return issubclass(obj, DecimalException)
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except TypeError:
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return False
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#Signals holds the exceptions
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Signals = filter(_filterfunc, globals().values())
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del _filterfunc
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# Map conditions (per the spec) to signals
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_condition_map = {ConversionSyntax:InvalidOperation,
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DivisionImpossible:InvalidOperation,
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DivisionUndefined:InvalidOperation,
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InvalidContext:InvalidOperation}
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##### Context Functions #######################################
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@ -2168,7 +2157,7 @@ class Context(object):
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return nc
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__copy__ = copy
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def _raise_error(self, error, explanation = None, *args):
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def _raise_error(self, condition, explanation = None, *args):
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"""Handles an error
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If the flag is in _ignored_flags, returns the default response.
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@ -2176,6 +2165,7 @@ class Context(object):
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trap_enabler is set, it reaises the exception. Otherwise, it returns
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the default value after incrementing the flag.
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"""
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error = _condition_map.get(condition, condition)
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if error in self._ignored_flags:
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#Don't touch the flag
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return error().handle(self, *args)
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@ -2183,7 +2173,7 @@ class Context(object):
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self.flags[error] += 1
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if not self.trap_enablers[error]:
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#The errors define how to handle themselves.
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return error().handle(self, *args)
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return condition().handle(self, *args)
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# Errors should only be risked on copies of the context
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#self._ignored_flags = []
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@ -2207,6 +2197,11 @@ class Context(object):
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for flag in flags:
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self._ignored_flags.remove(flag)
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def __hash__(self):
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"""A Context cannot be hashed."""
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# We inherit object.__hash__, so we must deny this explicitly
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raise TypeError, "Cannot hash a Context."
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def Etiny(self):
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"""Returns Etiny (= Emin - prec + 1)"""
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return int(self.Emin - self.prec + 1)
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@ -60,12 +60,12 @@ EXTENDEDERRORTEST = False
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#Map the test cases' error names to the actual errors
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ErrorNames = {'clamped' : Clamped,
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'conversion_syntax' : ConversionSyntax,
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'conversion_syntax' : InvalidOperation,
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'division_by_zero' : DivisionByZero,
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'division_impossible' : DivisionImpossible,
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'division_undefined' : DivisionUndefined,
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'division_impossible' : InvalidOperation,
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'division_undefined' : InvalidOperation,
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'inexact' : Inexact,
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'invalid_context' : InvalidContext,
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'invalid_context' : InvalidOperation,
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'invalid_operation' : InvalidOperation,
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'overflow' : Overflow,
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'rounded' : Rounded,
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@ -131,6 +131,7 @@ class DecimalTest(unittest.TestCase):
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return
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for line in open(file).xreadlines():
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line = line.replace('\r\n', '').replace('\n', '')
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#print line
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try:
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t = self.eval_line(line)
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except ConversionSyntax:
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@ -648,7 +649,6 @@ class DecimalArithmeticOperatorsTest(unittest.TestCase):
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self.assertEqual(d1, Decimal('-0.625'))
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def test_floor_division(self):
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'''Test floor division in all its ways.'''
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d1 = Decimal('5')
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d2 = Decimal('2')
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@ -676,7 +676,6 @@ class DecimalArithmeticOperatorsTest(unittest.TestCase):
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self.assertEqual(d1, Decimal('1'))
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def test_powering(self):
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'''Test powering in all its ways.'''
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d1 = Decimal('5')
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d2 = Decimal('2')
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