Merge branch 'master' into fix-issue-10244

11 files changed, 256 insertions, 53 deletions

diff --git a/numpy/polynomial/__init__.py b/numpy/polynomial/__init__.py
index 43b2caba3..c832094e2 100644
--- a/numpy/polynomial/__init__.py
+++ b/numpy/polynomial/__init__.py
@@ -12,6 +12,107 @@ all operations on polynomials, including evaluation at an argument, are
 implemented as operations on the coefficients.  Additional (module-specific)
 information can be found in the docstring for the module of interest.
 
+This package provides *convenience classes* for each of six different kinds
+of polynomials:
+
+         ============    ================
+         **Name**        **Provides**
+         ============    ================
+         Polynomial      Power series
+         Chebyshev       Chebyshev series
+         Legendre        Legendre series
+         Laguerre        Laguerre series
+         Hermite         Hermite series
+         HermiteE        HermiteE series
+         ============    ================
+
+These *convenience classes* provide a consistent interface for creating,
+manipulating, and fitting data with polynomials of different bases.
+The convenience classes are the preferred interface for the `~numpy.polynomial`
+package, and are available from the `numpy.polynomial` namespace.
+This eliminates the need to
+navigate to the corresponding submodules, e.g. ``np.polynomial.Polynomial``
+or ``np.polynomial.Chebyshev`` instead of
+``np.polynomial.polynomial.Polynomial`` or 
+``np.polynomial.chebyshev.Chebyshev``, respectively.
+The classes provide a more consistent and concise interface than the
+type-specific functions defined in the submodules for each type of polynomial.
+For example, to fit a Chebyshev polynomial with degree ``1`` to data given
+by arrays ``xdata`` and ``ydata``, the 
+`~chebyshev.Chebyshev.fit` class method::
+
+    >>> from numpy.polynomial import Chebyshev
+    >>> c = Chebyshev.fit(xdata, ydata, deg=1)
+
+is preferred over the `chebyshev.chebfit` function from the 
+`numpy.polynomial.chebyshev` module::
+
+    >>> from numpy.polynomial.chebyshev import chebfit
+    >>> c = chebfit(xdata, ydata, deg=1)
+
+See :doc:`routines.polynomials.classes` for more details.
+
+Convenience Classes
+===================
+
+The following lists the various constants and methods common to all of
+the classes representing the various kinds of polynomials. In the following,
+the term ``Poly`` represents any one of the convenience classes (e.g.
+``Polynomial``, ``Chebyshev``, ``Hermite``, etc.) while the lowercase ``p``
+represents an **instance** of a polynomial class.
+
+Constants
+---------
+
+- ``Poly.domain``     -- Default domain
+- ``Poly.window``     -- Default window
+- ``Poly.basis_name`` -- String used to represent the basis
+- ``Poly.maxpower``   -- Maximum value ``n`` such that ``p**n`` is allowed
+- ``Poly.nickname``   -- String used in printing
+
+Creation
+--------
+
+Methods for creating polynomial instances.
+
+- ``Poly.basis(degree)``    -- Basis polynomial of given degree
+- ``Poly.identity()``       -- ``p`` where ``p(x) = x`` for all ``x``
+- ``Poly.fit(x, y, deg)``   -- ``p`` of degree ``deg`` with coefficients 
+  determined by the least-squares fit to the data ``x``, ``y``
+- ``Poly.fromroots(roots)`` -- ``p`` with specified roots
+- ``p.copy()``              -- Create a copy of ``p``
+
+Conversion
+----------
+
+Methods for converting a polynomial instance of one kind to another.
+
+- ``p.cast(Poly)``    -- Convert ``p`` to instance of kind ``Poly``
+- ``p.convert(Poly)`` -- Convert ``p`` to instance of kind ``Poly`` or map
+  between ``domain`` and ``window``
+
+Calculus
+--------
+- ``p.deriv()`` -- Take the derivative of ``p``
+- ``p.integ()`` -- Integrate ``p``
+
+Validation
+----------
+- ``Poly.has_samecoef(p1, p2)``   -- Check if coefficients match
+- ``Poly.has_samedomain(p1, p2)`` -- Check if domains match
+- ``Poly.has_sametype(p1, p2)``   -- Check if types match
+- ``Poly.has_samewindow(p1, p2)`` -- Check if windows match
+
+Misc
+----
+- ``p.linspace()`` -- Return ``x, p(x)`` at equally-spaced points in ``domain``
+- ``p.mapparms()`` -- Return the parameters for the linear mapping between
+  ``domain`` and ``window``.
+- ``p.roots()``    -- Return the roots of `p`.
+- ``p.trim()``     -- Remove trailing coefficients.
+- ``p.cutdeg(degree)`` -- Truncate p to given degree
+- ``p.truncate(size)`` -- Truncate p to given size
+
 """
 from .polynomial import Polynomial
 from .chebyshev import Chebyshev
diff --git a/numpy/polynomial/__init__.pyi b/numpy/polynomial/__init__.pyi
new file mode 100644
index 000000000..817ba22ac
--- /dev/null
+++ b/numpy/polynomial/__init__.pyi
@@ -0,0 +1,9 @@
+from typing import Any
+
+Polynomial: Any
+Chebyshev: Any
+Legendre: Any
+Hermite: Any
+HermiteE: Any
+Laguerre: Any
+set_default_printstyle: Any
diff --git a/numpy/polynomial/_polybase.py b/numpy/polynomial/_polybase.py
index f4a67a222..59c380f10 100644
--- a/numpy/polynomial/_polybase.py
+++ b/numpy/polynomial/_polybase.py
@@ -547,8 +547,8 @@ class ABCPolyBase(abc.ABC):
         othercoef = self._get_coefficients(other)
         try:
             quo, rem = self._div(self.coef, othercoef)
-        except ZeroDivisionError as e:
-            raise e
+        except ZeroDivisionError:
+            raise
         except Exception:
             return NotImplemented
         quo = self.__class__(quo, self.domain, self.window)
@@ -605,8 +605,8 @@ class ABCPolyBase(abc.ABC):
     def __rdivmod__(self, other):
         try:
             quo, rem = self._div(other, self.coef)
-        except ZeroDivisionError as e:
-            raise e
+        except ZeroDivisionError:
+            raise
         except Exception:
             return NotImplemented
         quo = self.__class__(quo, self.domain, self.window)
diff --git a/numpy/polynomial/chebyshev.py b/numpy/polynomial/chebyshev.py
index d99fd98f5..6745c9371 100644
--- a/numpy/polynomial/chebyshev.py
+++ b/numpy/polynomial/chebyshev.py
@@ -477,8 +477,6 @@ def chebline(off, scl):
     """
     Chebyshev series whose graph is a straight line.
 
-
-
     Parameters
     ----------
     off, scl : scalars
@@ -492,7 +490,11 @@ def chebline(off, scl):
 
     See Also
     --------
-    polyline
+    numpy.polynomial.polynomial.polyline
+    numpy.polynomial.legendre.legline
+    numpy.polynomial.laguerre.lagline
+    numpy.polynomial.hermite.hermline
+    numpy.polynomial.hermite_e.hermeline
 
     Examples
     --------
@@ -545,7 +547,11 @@ def chebfromroots(roots):
 
     See Also
     --------
-    polyfromroots, legfromroots, lagfromroots, hermfromroots, hermefromroots
+    numpy.polynomial.polynomial.polyfromroots
+    numpy.polynomial.legendre.legfromroots
+    numpy.polynomial.laguerre.lagfromroots
+    numpy.polynomial.hermite.hermfromroots
+    numpy.polynomial.hermite_e.hermefromroots
 
     Examples
     --------
@@ -764,7 +770,7 @@ def chebdiv(c1, c2):
 
     See Also
     --------
-    chebadd, chebsub, chemulx, chebmul, chebpow
+    chebadd, chebsub, chebmulx, chebmul, chebpow
 
     Notes
     -----
@@ -1601,7 +1607,7 @@ def chebfit(x, y, deg, rcond=None, full=False, w=None):
         sv -- singular values of the scaled Vandermonde matrix
         rcond -- value of `rcond`.
 
-        For more details, see `linalg.lstsq`.
+        For more details, see `numpy.linalg.lstsq`.
 
     Warns
     -----
@@ -1615,11 +1621,15 @@ def chebfit(x, y, deg, rcond=None, full=False, w=None):
 
     See Also
     --------
-    polyfit, legfit, lagfit, hermfit, hermefit
+    numpy.polynomial.polynomial.polyfit
+    numpy.polynomial.legendre.legfit
+    numpy.polynomial.laguerre.lagfit
+    numpy.polynomial.hermite.hermfit
+    numpy.polynomial.hermite_e.hermefit
     chebval : Evaluates a Chebyshev series.
     chebvander : Vandermonde matrix of Chebyshev series.
     chebweight : Chebyshev weight function.
-    linalg.lstsq : Computes a least-squares fit from the matrix.
+    numpy.linalg.lstsq : Computes a least-squares fit from the matrix.
     scipy.interpolate.UnivariateSpline : Computes spline fits.
 
     Notes
@@ -1729,7 +1739,11 @@ def chebroots(c):
 
     See Also
     --------
-    polyroots, legroots, lagroots, hermroots, hermeroots
+    numpy.polynomial.polynomial.polyroots
+    numpy.polynomial.legendre.legroots
+    numpy.polynomial.laguerre.lagroots
+    numpy.polynomial.hermite.hermroots
+    numpy.polynomial.hermite_e.hermeroots
 
     Notes
     -----
diff --git a/numpy/polynomial/hermite.py b/numpy/polynomial/hermite.py
index 280cad39e..c679c5298 100644
--- a/numpy/polynomial/hermite.py
+++ b/numpy/polynomial/hermite.py
@@ -233,7 +233,11 @@ def hermline(off, scl):
 
     See Also
     --------
-    polyline, chebline
+    numpy.polynomial.polynomial.polyline
+    numpy.polynomial.chebyshev.chebline
+    numpy.polynomial.legendre.legline
+    numpy.polynomial.laguerre.lagline
+    numpy.polynomial.hermite_e.hermeline
 
     Examples
     --------
@@ -286,7 +290,11 @@ def hermfromroots(roots):
 
     See Also
     --------
-    polyfromroots, legfromroots, lagfromroots, chebfromroots, hermefromroots
+    numpy.polynomial.polynomial.polyfromroots
+    numpy.polynomial.legendre.legfromroots
+    numpy.polynomial.laguerre.lagfromroots
+    numpy.polynomial.chebyshev.chebfromroots
+    numpy.polynomial.hermite_e.hermefromroots
 
     Examples
     --------
@@ -1322,7 +1330,7 @@ def hermfit(x, y, deg, rcond=None, full=False, w=None):
         sv -- singular values of the scaled Vandermonde matrix
         rcond -- value of `rcond`.
 
-        For more details, see `linalg.lstsq`.
+        For more details, see `numpy.linalg.lstsq`.
 
     Warns
     -----
@@ -1336,11 +1344,15 @@ def hermfit(x, y, deg, rcond=None, full=False, w=None):
 
     See Also
     --------
-    chebfit, legfit, lagfit, polyfit, hermefit
+    numpy.polynomial.chebyshev.chebfit
+    numpy.polynomial.legendre.legfit
+    numpy.polynomial.laguerre.lagfit
+    numpy.polynomial.polynomial.polyfit
+    numpy.polynomial.hermite_e.hermefit
     hermval : Evaluates a Hermite series.
     hermvander : Vandermonde matrix of Hermite series.
     hermweight : Hermite weight function
-    linalg.lstsq : Computes a least-squares fit from the matrix.
+    numpy.linalg.lstsq : Computes a least-squares fit from the matrix.
     scipy.interpolate.UnivariateSpline : Computes spline fits.
 
     Notes
@@ -1457,7 +1469,11 @@ def hermroots(c):
 
     See Also
     --------
-    polyroots, legroots, lagroots, chebroots, hermeroots
+    numpy.polynomial.polynomial.polyroots
+    numpy.polynomial.legendre.legroots
+    numpy.polynomial.laguerre.lagroots
+    numpy.polynomial.chebyshev.chebroots
+    numpy.polynomial.hermite_e.hermeroots
 
     Notes
     -----
diff --git a/numpy/polynomial/hermite_e.py b/numpy/polynomial/hermite_e.py
index 9b3b25105..1ce8ebe04 100644
--- a/numpy/polynomial/hermite_e.py
+++ b/numpy/polynomial/hermite_e.py
@@ -218,8 +218,6 @@ def hermeline(off, scl):
     """
     Hermite series whose graph is a straight line.
 
-
-
     Parameters
     ----------
     off, scl : scalars
@@ -233,7 +231,11 @@ def hermeline(off, scl):
 
     See Also
     --------
-    polyline, chebline
+    numpy.polynomial.polynomial.polyline
+    numpy.polynomial.chebyshev.chebline
+    numpy.polynomial.legendre.legline
+    numpy.polynomial.laguerre.lagline
+    numpy.polynomial.hermite.hermline
 
     Examples
     --------
@@ -287,7 +289,11 @@ def hermefromroots(roots):
 
     See Also
     --------
-    polyfromroots, legfromroots, lagfromroots, hermfromroots, chebfromroots
+    numpy.polynomial.polynomial.polyfromroots
+    numpy.polynomial.legendre.legfromroots
+    numpy.polynomial.laguerre.lagfromroots
+    numpy.polynomial.hermite.hermfromroots
+    numpy.polynomial.chebyshev.chebfromroots
 
     Examples
     --------
@@ -1315,7 +1321,7 @@ def hermefit(x, y, deg, rcond=None, full=False, w=None):
         sv -- singular values of the scaled Vandermonde matrix
         rcond -- value of `rcond`.
 
-        For more details, see `linalg.lstsq`.
+        For more details, see `numpy.linalg.lstsq`.
 
     Warns
     -----
@@ -1329,11 +1335,15 @@ def hermefit(x, y, deg, rcond=None, full=False, w=None):
 
     See Also
     --------
-    chebfit, legfit, polyfit, hermfit, polyfit
+    numpy.polynomial.chebyshev.chebfit
+    numpy.polynomial.legendre.legfit
+    numpy.polynomial.polynomial.polyfit
+    numpy.polynomial.hermite.hermfit
+    numpy.polynomial.laguerre.lagfit
     hermeval : Evaluates a Hermite series.
     hermevander : pseudo Vandermonde matrix of Hermite series.
     hermeweight : HermiteE weight function.
-    linalg.lstsq : Computes a least-squares fit from the matrix.
+    numpy.linalg.lstsq : Computes a least-squares fit from the matrix.
     scipy.interpolate.UnivariateSpline : Computes spline fits.
 
     Notes
@@ -1452,7 +1462,11 @@ def hermeroots(c):
 
     See Also
     --------
-    polyroots, legroots, lagroots, hermroots, chebroots
+    numpy.polynomial.polynomial.polyroots
+    numpy.polynomial.legendre.legroots
+    numpy.polynomial.laguerre.lagroots
+    numpy.polynomial.hermite.hermroots
+    numpy.polynomial.chebyshev.chebroots
 
     Notes
     -----
diff --git a/numpy/polynomial/laguerre.py b/numpy/polynomial/laguerre.py
index c1db13215..9cff0b71c 100644
--- a/numpy/polynomial/laguerre.py
+++ b/numpy/polynomial/laguerre.py
@@ -214,8 +214,6 @@ def lagline(off, scl):
     """
     Laguerre series whose graph is a straight line.
 
-
-
     Parameters
     ----------
     off, scl : scalars
@@ -229,7 +227,11 @@ def lagline(off, scl):
 
     See Also
     --------
-    polyline, chebline
+    numpy.polynomial.polynomial.polyline
+    numpy.polynomial.chebyshev.chebline
+    numpy.polynomial.legendre.legline
+    numpy.polynomial.hermite.hermline
+    numpy.polynomial.hermite_e.hermeline
 
     Examples
     --------
@@ -282,7 +284,11 @@ def lagfromroots(roots):
 
     See Also
     --------
-    polyfromroots, legfromroots, chebfromroots, hermfromroots, hermefromroots
+    numpy.polynomial.polynomial.polyfromroots
+    numpy.polynomial.legendre.legfromroots
+    numpy.polynomial.chebyshev.chebfromroots
+    numpy.polynomial.hermite.hermfromroots
+    numpy.polynomial.hermite_e.hermefromroots
 
     Examples
     --------
@@ -1321,7 +1327,7 @@ def lagfit(x, y, deg, rcond=None, full=False, w=None):
         sv -- singular values of the scaled Vandermonde matrix
         rcond -- value of `rcond`.
 
-        For more details, see `linalg.lstsq`.
+        For more details, see `numpy.linalg.lstsq`.
 
     Warns
     -----
@@ -1335,11 +1341,15 @@ def lagfit(x, y, deg, rcond=None, full=False, w=None):
 
     See Also
     --------
-    chebfit, legfit, polyfit, hermfit, hermefit
+    numpy.polynomial.polynomial.polyfit
+    numpy.polynomial.legendre.legfit
+    numpy.polynomial.chebyshev.chebfit
+    numpy.polynomial.hermite.hermfit
+    numpy.polynomial.hermite_e.hermefit
     lagval : Evaluates a Laguerre series.
     lagvander : pseudo Vandermonde matrix of Laguerre series.
     lagweight : Laguerre weight function.
-    linalg.lstsq : Computes a least-squares fit from the matrix.
+    numpy.linalg.lstsq : Computes a least-squares fit from the matrix.
     scipy.interpolate.UnivariateSpline : Computes spline fits.
 
     Notes
@@ -1455,7 +1465,11 @@ def lagroots(c):
 
     See Also
     --------
-    polyroots, legroots, chebroots, hermroots, hermeroots
+    numpy.polynomial.polynomial.polyroots
+    numpy.polynomial.legendre.legroots
+    numpy.polynomial.chebyshev.chebroots
+    numpy.polynomial.hermite.hermroots
+    numpy.polynomial.hermite_e.hermeroots
 
     Notes
     -----
diff --git a/numpy/polynomial/legendre.py b/numpy/polynomial/legendre.py
index 7b5b665f2..427f9f82f 100644
--- a/numpy/polynomial/legendre.py
+++ b/numpy/polynomial/legendre.py
@@ -243,7 +243,11 @@ def legline(off, scl):
 
     See Also
     --------
-    polyline, chebline
+    numpy.polynomial.polynomial.polyline
+    numpy.polynomial.chebyshev.chebline
+    numpy.polynomial.laguerre.lagline
+    numpy.polynomial.hermite.hermline
+    numpy.polynomial.hermite_e.hermeline
 
     Examples
     --------
@@ -296,7 +300,11 @@ def legfromroots(roots):
 
     See Also
     --------
-    polyfromroots, chebfromroots, lagfromroots, hermfromroots, hermefromroots
+    numpy.polynomial.polynomial.polyfromroots
+    numpy.polynomial.chebyshev.chebfromroots
+    numpy.polynomial.laguerre.lagfromroots
+    numpy.polynomial.hermite.hermfromroots
+    numpy.polynomial.hermite_e.hermefromroots
 
     Examples
     --------
@@ -1343,7 +1351,7 @@ def legfit(x, y, deg, rcond=None, full=False, w=None):
         sv -- singular values of the scaled Vandermonde matrix
         rcond -- value of `rcond`.
 
-        For more details, see `linalg.lstsq`.
+        For more details, see `numpy.linalg.lstsq`.
 
     Warns
     -----
@@ -1357,11 +1365,15 @@ def legfit(x, y, deg, rcond=None, full=False, w=None):
 
     See Also
     --------
-    chebfit, polyfit, lagfit, hermfit, hermefit
+    numpy.polynomial.polynomial.polyfit
+    numpy.polynomial.chebyshev.chebfit
+    numpy.polynomial.laguerre.lagfit
+    numpy.polynomial.hermite.hermfit
+    numpy.polynomial.hermite_e.hermefit
     legval : Evaluates a Legendre series.
     legvander : Vandermonde matrix of Legendre series.
     legweight : Legendre weight function (= 1).
-    linalg.lstsq : Computes a least-squares fit from the matrix.
+    numpy.linalg.lstsq : Computes a least-squares fit from the matrix.
     scipy.interpolate.UnivariateSpline : Computes spline fits.
 
     Notes
@@ -1470,7 +1482,11 @@ def legroots(c):
 
     See Also
     --------
-    polyroots, chebroots, lagroots, hermroots, hermeroots
+    numpy.polynomial.polynomial.polyroots
+    numpy.polynomial.chebyshev.chebroots
+    numpy.polynomial.laguerre.lagroots
+    numpy.polynomial.hermite.hermroots
+    numpy.polynomial.hermite_e.hermeroots
 
     Notes
     -----
diff --git a/numpy/polynomial/polynomial.py b/numpy/polynomial/polynomial.py
index 83693441f..1baa7d870 100644
--- a/numpy/polynomial/polynomial.py
+++ b/numpy/polynomial/polynomial.py
@@ -127,7 +127,11 @@ def polyline(off, scl):
 
     See Also
     --------
-    chebline
+    numpy.polynomial.chebyshev.chebline
+    numpy.polynomial.legendre.legline
+    numpy.polynomial.laguerre.lagline
+    numpy.polynomial.hermite.hermline
+    numpy.polynomial.hermite_e.hermeline
 
     Examples
     --------
@@ -179,8 +183,11 @@ def polyfromroots(roots):
 
     See Also
     --------
-    chebfromroots, legfromroots, lagfromroots, hermfromroots
-    hermefromroots
+    numpy.polynomial.chebyshev.chebfromroots
+    numpy.polynomial.legendre.legfromroots
+    numpy.polynomial.laguerre.lagfromroots
+    numpy.polynomial.hermite.hermfromroots
+    numpy.polynomial.hermite_e.hermefromroots
 
     Notes
     -----
@@ -1267,7 +1274,7 @@ def polyfit(x, y, deg, rcond=None, full=False, w=None):
         sv -- singular values of the scaled Vandermonde matrix
         rcond -- value of `rcond`.
 
-        For more details, see `linalg.lstsq`.
+        For more details, see `numpy.linalg.lstsq`.
 
     Raises
     ------
@@ -1281,10 +1288,14 @@ def polyfit(x, y, deg, rcond=None, full=False, w=None):
 
     See Also
     --------
-    chebfit, legfit, lagfit, hermfit, hermefit
+    numpy.polynomial.chebyshev.chebfit
+    numpy.polynomial.legendre.legfit
+    numpy.polynomial.laguerre.lagfit
+    numpy.polynomial.hermite.hermfit
+    numpy.polynomial.hermite_e.hermefit
     polyval : Evaluates a polynomial.
     polyvander : Vandermonde matrix for powers.
-    linalg.lstsq : Computes a least-squares fit from the matrix.
+    numpy.linalg.lstsq : Computes a least-squares fit from the matrix.
     scipy.interpolate.UnivariateSpline : Computes spline fits.
 
     Notes
@@ -1411,7 +1422,11 @@ def polyroots(c):
 
     See Also
     --------
-    chebroots
+    numpy.polynomial.chebyshev.chebroots
+    numpy.polynomial.legendre.legroots
+    numpy.polynomial.laguerre.lagroots
+    numpy.polynomial.hermite.hermroots
+    numpy.polynomial.hermite_e.hermeroots
 
     Notes
     -----
diff --git a/numpy/polynomial/setup.py b/numpy/polynomial/setup.py
index 641464518..b58e867a1 100644
--- a/numpy/polynomial/setup.py
+++ b/numpy/polynomial/setup.py
@@ -2,6 +2,7 @@ def configuration(parent_package='',top_path=None):
     from numpy.distutils.misc_util import Configuration
     config = Configuration('polynomial', parent_package, top_path)
     config.add_subpackage('tests')
+    config.add_data_files('*.pyi')
     return config
 
 if __name__ == '__main__':
diff --git a/numpy/polynomial/tests/test_printing.py b/numpy/polynomial/tests/test_printing.py
index 27a8ab9f2..4e9902a69 100644
--- a/numpy/polynomial/tests/test_printing.py
+++ b/numpy/polynomial/tests/test_printing.py
@@ -85,7 +85,7 @@ class TestStrUnicodeSuperSubscripts:
 class TestStrAscii:
 
     @pytest.fixture(scope='class', autouse=True)
-    def use_unicode(self):
+    def use_ascii(self):
         poly.set_default_printstyle('ascii')
 
     @pytest.mark.parametrize(('inp', 'tgt'), (
@@ -161,7 +161,10 @@ class TestStrAscii:
 
 
 class TestLinebreaking:
-    poly.set_default_printstyle('ascii')
+
+    @pytest.fixture(scope='class', autouse=True)
+    def use_ascii(self):
+        poly.set_default_printstyle('ascii')
 
     def test_single_line_one_less(self):
         # With 'ascii' style, len(str(p)) is default linewidth - 1 (i.e. 74)
@@ -283,19 +286,19 @@ def test_nonnumeric_object_coefficients(coefs, tgt):
 
 class TestFormat:
     def test_format_unicode(self):
-        poly.Polynomial._use_unicode = False
+        poly.set_default_printstyle('ascii')
         p = poly.Polynomial([1, 2, 0, -1])
         assert_equal(format(p, 'unicode'), "1.0 + 2.0·x¹ + 0.0·x² - 1.0·x³")
 
     def test_format_ascii(self):
-        poly.Polynomial._use_unicode = True
+        poly.set_default_printstyle('unicode')
         p = poly.Polynomial([1, 2, 0, -1])
         assert_equal(
             format(p, 'ascii'), "1.0 + 2.0 x**1 + 0.0 x**2 - 1.0 x**3"
         )
 
     def test_empty_formatstr(self):
-        poly.Polynomial._use_unicode = False
+        poly.set_default_printstyle('ascii')
         p = poly.Polynomial([1, 2, 3])
         assert_equal(format(p), "1.0 + 2.0 x**1 + 3.0 x**2")
         assert_equal(f"{p}", "1.0 + 2.0 x**1 + 3.0 x**2")