On line 502, self.symbol.copy() was called, which
causes an AttributeError, since self.symbol is a
string, so it doesn't have a copy() method. To fix
it, I simply removed the copy() and directly assigned
the string.

* limit the number of decimals in Polynomial representation

* tests pass

* parenthesize exponential notation in polynomials

* fixed a long line warning

* added polynomial printoptions tests

* polynomial printoptions typo fixed

* made switch to exp notation in polynomial display more natural

* added a test on switching polynomials to exp notation

* fixed linter errors/warnings

* support for nanstr and infstr printoptions in polynomials

* 10^8 threshold for switching to exp notation when displaying polynomials

* merged in PR #21696 fixing issue #21695

* made linter happy

* made some docstring tests pass

* fixed the docs

Co-authored-by: Lev Maximov <lev.maximov@gmail.com>

Adds a symbol attribute to the polynomials from the np.polynomial package to allow the user to control/modify the symbol used to represent the independent variable for a polynomial expression. This attribute corresponds to the variable attribute of the poly1d class from the old np.lib.polynomial module.

Marked as draft for now as it depends on #15666 - all _str* and _repr* methods of ABCPolyBase and derived classes would need to be modified (and tested) to support this change.

Co-authored-by: Warren Weckesser <warren.weckesser@gmail.com>

DOC: fix docstring formatting of polynomial fit method return values.

Fixes #19897

The 2nd return value of the following methods/functions were badly
formatted and the list was all appearing in a single line. Changed them
to separate points which are rendered nicely.
 - numpy.polyfit
 - numpy.ma.polyfit
 - numpy.polynomial.polynomial.polyfit
 - numpy.polynomial.polynomial.Polynomial.fit
 - numpy.polynomial.chebyshev.chebfit
 - numpy.polynomial.chebyshev.Chebyshev.fit
 - numpy.polynomial.hermite.hermfit
 - numpy.polynomial.hermite.Hermite.fit
 - numpy.polynomial.hermite_e.hermefit
 - numpy.polynomial.hermite_e.HermiteE.fit
 - numpy.polynomial.laguerre.lagfit
 - numpy.polynomial.laguerre.Laguerre.fit
 - numpy.polynomial.legendre.legfit
 - numpy.polynomial.legendre.Legendre.fit

Also fixed erroneous links to `numpy.full` which were actually referring
to the `full` argument. Changed those to code strings (double backticks)
from single backticks.

Also fixed formatting issues in the 3rd return value of numpy.polyfit
(and hence also numpy.ma.polyfit).

* DOC: Adjust polyfit doc to clarify the meaning of w

cov='unscaled', in particular, had inconsistently referred to a weight
of 1/sigma**2, while the doc for w says it should be equal to 1/sigma.
This change clarifies w to comport with more typical meanings of
weights in weighted least squares, and makes clear that cov='unscaled'
is appropriate when the weight w**2 = 1/sigma**2.

See Issue #5261 for more discussion of the errors/confusion in
the previous doc string.

* Update doc text for w in all polynomial module fit functions

Co-authored-by: Stefan van der Walt <sjvdwalt@gmail.com>
Co-authored-by: Ross Barnowski <rossbar@berkeley.edu>

Numpydoc format says that the colon need o be omitted if there is no
type, there were also some empty Examples Sections

... or when the input isn't/cannot be a set.  I left a few usages, e.g.
in random sampling, where "set" is reasonable as informal description of
an array as the order doesn't matter; however, for e.g. np.gradient the
order of the returned list is clearly important, so "set" is wrong.

Also some other minor doc edits noticed during the grepping: using
`shape` instead of `form` in `cov` is consistent with most other places;
the wording in `Polynomial.trim` now matches other methods on the same
class.

Single backticks default role is reference, while here it seem to be for
verbatim. Fix it in a couple of places.