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(python2.1-ref.info)Arithmetic conversions

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Arithmetic conversions
======================

When a description of an arithmetic operator below uses the phrase "the
numeric arguments are converted to a common type," the arguments are
coerced using the coercion rules listed at the end of chapter 3.  If
both arguments are standard numeric types, the following coercions are
applied:

   * If either argument is a complex number, the other is converted to
     complex;

   * otherwise, if either argument is a floating point number, the
     other is converted to floating point;

   * otherwise, if either argument is a long integer, the other is
     converted to long integer;

   * otherwise, both must be plain integers and no conversion is
     necessary.

Some additional rules apply for certain operators (e.g., a string left
argument to the `%' operator). Extensions can define their own
coercions.