Add a _check_getitem helper to go with _check_in_list/_check_isinstance.

anntzer · anntzer · commit 08bff55b5970 · 2019-06-30T20:58:21.000+02:00
Also rename the first parameter of these helpers to start with an
underscore, to mark them as effectively positional-only.
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -141,8 +141,7 @@ def get_title(self, loc="center"):
         titles = {'left': self._left_title,
                   'center': self.title,
                   'right': self._right_title}
-        cbook._check_in_list(titles, loc=loc.lower())
-        title = titles[loc.lower()]
+        title = cbook._check_getitem(titles, loc=loc.lower())
         return title.get_text()
 
     def set_title(self, label, fontdict=None, loc=None, pad=None,
@@ -193,8 +192,7 @@ def set_title(self, label, fontdict=None, loc=None, pad=None,
         titles = {'left': self._left_title,
                   'center': self.title,
                   'right': self._right_title}
-        cbook._check_in_list(titles, loc=loc.lower())
-        title = titles[loc.lower()]
+        title = cbook._check_getitem(titles, loc=loc.lower())
         default = {
             'fontsize': rcParams['axes.titlesize'],
             'fontweight': rcParams['axes.titleweight'],
diff --git a/lib/matplotlib/axis.py b/lib/matplotlib/axis.py
@@ -1987,12 +1987,9 @@ def set_label_position(self, position):
         ----------
         position : {'top', 'bottom'}
         """
-        if position == 'top':
-            self.label.set_verticalalignment('baseline')
-        elif position == 'bottom':
-            self.label.set_verticalalignment('top')
-        else:
-            raise ValueError("Position accepts only 'top' or 'bottom'")
+        self.label.set_verticalalignment(cbook._check_getitem({
+            'top': 'baseline', 'bottom': 'top',
+        }, position=position))
         self.label_position = position
         self.stale = True
 
@@ -2281,12 +2278,9 @@ def set_label_position(self, position):
         """
         self.label.set_rotation_mode('anchor')
         self.label.set_horizontalalignment('center')
-        if position == 'left':
-            self.label.set_verticalalignment('bottom')
-        elif position == 'right':
-            self.label.set_verticalalignment('top')
-        else:
-            raise ValueError("Position accepts only 'left' or 'right'")
+        self.label.set_verticalalignment(cbook._check_getitem({
+            'left': 'bottom', 'right': 'top',
+        }, position=position))
         self.label_position = position
         self.stale = True
 
diff --git a/lib/matplotlib/backends/backend_cairo.py b/lib/matplotlib/backends/backend_cairo.py
@@ -338,9 +338,8 @@ def set_alpha(self, alpha):
         # one for False.
 
     def set_capstyle(self, cs):
-        cbook._check_in_list(('butt', 'round', 'projecting'), capstyle=cs)
+        self.ctx.set_line_cap(cbook._check_getitem(self._capd, capstyle=cs))
         self._capstyle = cs
-        self.ctx.set_line_cap(self._capd[cs])
 
     def set_clip_rectangle(self, rectangle):
         if not rectangle:
@@ -382,9 +381,8 @@ def get_rgb(self):
         return self.ctx.get_source().get_rgba()[:3]
 
     def set_joinstyle(self, js):
-        cbook._check_in_list(('miter', 'round', 'bevel'), joinstyle=js)
+        self.ctx.set_line_join(cbook._check_getitem(self._joind, joinstyle=js))
         self._joinstyle = js
-        self.ctx.set_line_join(self._joind[js])
 
     def set_linewidth(self, w):
         self._linewidth = float(w)
diff --git a/lib/matplotlib/cbook/__init__.py b/lib/matplotlib/cbook/__init__.py
@@ -2050,17 +2050,23 @@ def _check_and_log_subprocess(command, logger, **kwargs):
     return report
 
 
-def _check_isinstance(types, **kwargs):
+# In the following _check_foo functions, the first parameter starts with an
+# underscore because it is intended to be positional-only (e.g., so that
+# `_check_isinstance([...], types=foo)` doesn't fail.
+
+
+def _check_isinstance(_types, **kwargs):
     """
     For each *key, value* pair in *kwargs*, check that *value* is an instance
-    of one of *types*; if not, raise an appropriate TypeError.
+    of one of *_types*; if not, raise an appropriate TypeError.
 
-    As a special case, a ``None`` entry in *types* is treated as NoneType.
+    As a special case, a ``None`` entry in *_types* is treated as NoneType.
 
     Examples
     --------
     >>> cbook._check_isinstance((SomeClass, None), arg=arg)
     """
+    types = _types
     if isinstance(types, type) or types is None:
         types = (types,)
     none_allowed = None in types
@@ -2084,17 +2090,40 @@ def type_name(tp):
                     type_name(type(v))))
 
 
-def _check_in_list(values, **kwargs):
+def _check_in_list(_values, **kwargs):
     """
-    For each *key, value* pair in *kwargs*, check that *value* is in *values*;
+    For each *key, value* pair in *kwargs*, check that *value* is in *_values*;
     if not, raise an appropriate ValueError.
 
     Examples
     --------
     >>> cbook._check_in_list(["foo", "bar"], arg=arg, other_arg=other_arg)
     """
+    values = _values
     for k, v in kwargs.items():
         if v not in values:
             raise ValueError(
                 "{!r} is not a valid value for {}; supported values are {}"
                 .format(v, k, ', '.join(map(repr, values))))
+
+
+def _check_getitem(_mapping, **kwargs):
+    """
+    *kwargs* must consist of a single *key, value* pair.  If *key* is in
+    *_mapping*, return ``_mapping[value]``; else, raise an appropriate
+    ValueError.
+
+    Examples
+    --------
+    >>> cbook._check_getitem({"foo": "bar"}, arg=arg)
+    """
+    mapping = _mapping
+    if len(kwargs) != 1:
+        raise ValueError("_check_getitem takes a single keyword argument")
+    (k, v), = kwargs.items()
+    try:
+        return mapping[v]
+    except KeyError:
+        raise ValueError(
+            "{!r} is not a valid value for {}; supported values are {}"
+            .format(v, k, ', '.join(map(repr, mapping)))) from None
diff --git a/lib/matplotlib/mathtext.py b/lib/matplotlib/mathtext.py
@@ -3340,8 +3340,8 @@ def parse(self, s, dpi = 72, prop = None):
         else:
             backend = self._backend_mapping[self._output]()
             fontset = rcParams['mathtext.fontset'].lower()
-            cbook._check_in_list(self._font_type_mapping, fontset=fontset)
-            fontset_class = self._font_type_mapping[fontset]
+            fontset_class = cbook._check_getitem(
+                self._font_type_mapping, fontset=fontset)
             font_output = fontset_class(prop, backend)
 
         fontsize = prop.get_size_in_points()
diff --git a/lib/matplotlib/offsetbox.py b/lib/matplotlib/offsetbox.py
@@ -1125,8 +1125,7 @@ def __init__(self, loc,
         self.set_child(child)
 
         if isinstance(loc, str):
-            cbook._check_in_list(self.codes, loc=loc)
-            loc = self.codes[loc]
+            loc = cbook._check_getitem(self.codes, loc=loc)
 
         self.loc = loc
         self.borderpad = borderpad
diff --git a/lib/matplotlib/testing/jpl_units/UnitDbl.py b/lib/matplotlib/testing/jpl_units/UnitDbl.py
@@ -47,8 +47,7 @@ def __init__(self, value, units):
         - value     The numeric value of the UnitDbl.
         - units     The string name of the units the value is in.
         """
-        cbook._check_in_list(self.allowed, units=units)
-        data = self.allowed[units]
+        data = cbook._check_getitem(self.allowed, units=units)
         self._value = float(value * data[0])
         self._units = data[1]
 
@@ -67,8 +66,7 @@ def convert(self, units):
         """
         if self._units == units:
             return self._value
-        cbook._check_in_list(self.allowed, units=units)
-        data = self.allowed[units]
+        data = cbook._check_getitem(self.allowed, units=units)
         if self._units != data[1]:
             raise ValueError(f"Error trying to convert to different units.\n"
                              f"    Invalid conversion requested.\n"
diff --git a/lib/mpl_toolkits/axisartist/axis_artist.py b/lib/mpl_toolkits/axisartist/axis_artist.py
@@ -452,8 +452,7 @@ def get_text(self):
                                top=("bottom", "center"))
 
     def set_default_alignment(self, d):
-        cbook._check_in_list(["left", "right", "top", "bottom"], d=d)
-        va, ha = self._default_alignments[d]
+        va, ha = cbook._check_getitem(self._default_alignments, d=d)
         self.set_va(va)
         self.set_ha(ha)
 
@@ -463,8 +462,7 @@ def set_default_alignment(self, d):
                            top=180)
 
     def set_default_angle(self, d):
-        cbook._check_in_list(["left", "right", "top", "bottom"], d=d)
-        self.set_rotation(self._default_angles[d])
+        self.set_rotation(cbook._check_getitem(self._default_angles, d=d))
 
     def set_axis_direction(self, d):
         """
@@ -852,8 +850,8 @@ def set_ticklabel_direction(self, tick_direction):
         ----------
         tick_direction : {"+", "-"}
         """
-        cbook._check_in_list(["+", "-"], tick_direction=tick_direction)
-        self._ticklabel_add_angle = {"+": 0, "-": 180}[tick_direction]
+        self._ticklabel_add_angle = cbook._check_getitem(
+            {"+": 0, "-": 180}, tick_direction=tick_direction)
 
     def invert_ticklabel_direction(self):
         self._ticklabel_add_angle = (self._ticklabel_add_angle + 180) % 360
@@ -871,8 +869,8 @@ def set_axislabel_direction(self, label_direction):
         ----------
         tick_direction : {"+", "-"}
         """
-        cbook._check_in_list(["+", "-"], label_direction=label_direction)
-        self._axislabel_add_angle = {"+": 0, "-": 180}[label_direction]
+        self._axislabel_add_angle = cbook._check_getitem(
+            {"+": 0, "-": 180}, label_direction=label_direction)
 
     def get_transform(self):
         return self.axes.transAxes + self.offset_transform
diff --git a/lib/mpl_toolkits/mplot3d/axes3d.py b/lib/mpl_toolkits/mplot3d/axes3d.py
@@ -993,15 +993,12 @@ def set_proj_type(self, proj_type):
 
         Parameters
         ----------
-        proj_type : str
-            Type of projection, accepts 'persp' and 'ortho'.
-
+        proj_type : {'persp', 'ortho'}
         """
-        cbook._check_in_list(['persp', 'ortho'], proj_type=proj_type)
-        if proj_type == 'persp':
-            self._projection = proj3d.persp_transformation
-        elif proj_type == 'ortho':
-            self._projection = proj3d.ortho_transformation
+        self._projection = cbook._check_getitem({
+            'persp': proj3d.persp_transformation,
+            'ortho': proj3d.ortho_transformation,
+        }, proj_type=proj_type)
 
     def get_proj(self):
         """
