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Availability: Unix.
Most computers carry out floating point operations
in conformance with the so-called IEEE-754 standard. On any real computer, some floating
point operations produce results that cannot be expressed as a normal floating point value.
For example, try
>>> import math
>>> math.exp(1000)
inf
>>> math.exp(1000) / math.exp(1000)
nan
(The example above will work on many platforms. DEC Alpha may be one exception.) "Inf"
is a special, non-numeric value in IEEE-754 that stands for "infinity", and "nan"
means "not a number." Note that, other than the non-numeric results, nothing special
happened when you asked Python to carry out those calculations. That is in fact the default
behaviour prescribed in the IEEE-754 standard, and if it works for you, stop reading now.
In some circumstances, it would be better to raise an exception and stop processing at the
point where the faulty operation was attempted. The fpectl module is
for use in that situation. It provides control over floating point units from several hardware
manufacturers, allowing the user to turn on the generation of SIGFPE
whenever any of the IEEE-754 exceptions Division by Zero, Overflow, or Invalid Operation
occurs. In tandem with a pair of wrapper macros that are inserted into the C code comprising
your python system, SIGFPE is trapped and converted into the Python FloatingPointError exception.
The fpectl module defines the following functions and may raise the
given exception:
-
- Turn on the generation of SIGFPE, and set up an appropriate
signal handler.
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- Reset default handling of floating point exceptions.
- exception FloatingPointError
- After turnon_sigfpe() has been executed, a floating point
operation that raises one of the IEEE-754 exceptions Division by Zero, Overflow, or
Invalid operation will in turn raise this standard Python exception.
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