Fix invalid range validators.

- The correct bound on margins value, documented in set_x/y/zmargin, is
  margin>-0.5.  Fix the docstring of margins() and the rc validators.
- The only constraints on tight/constrained layout margins is left<right
  and bottom<top, but values outside of [0, 1] can in fact be valid.  It
  would be annoying to enforce this at the rcparams level (this would
  force the user to update individual rcparams in a careful order), so
  just don't bother validating the values beyond "float".
- Remove the somewhat overengineered _range_validators.
- Move the comment about the values of figure.constrained_layout.h/w_pad
  to the default matplotlibrc (in rcsetup.py it was far away from the
  actual values, which made things a bit weird).  Also reword a bit.

Author: anntzer

lib/matplotlib/_constrained_layout.py

@@ -678,7 +678,7 @@ def reposition_colorbar(layoutgrids, cbax, renderer, *, offset=None):
         width and height padding (in fraction of figure)
     hspace, wspace : float
         width and height padding as fraction of figure size divided by
-        number of  columns or rows
+        number of columns or rows
     margin : array-like
         offset the colorbar needs to be pushed to in order to
         account for multiple colorbars

lib/matplotlib/axes/_base.py

@@ -2665,10 +2665,10 @@ def margins(self, *margins, x=None, y=None, tight=True):
 
         The padding added to each limit of the Axes is the *margin*
         times the data interval. All input parameters must be floats
-        within the range [0, 1]. Passing both positional and keyword
+        greater than -0.5. Passing both positional and keyword
         arguments is invalid and will raise a TypeError. If no
         arguments (positional or otherwise) are provided, the current
-        margins will remain in place and simply be returned.
+        margins will remain unchanged and simply be returned.
 
         Specifying any margin changes only the autoscaling; for example,
         if *xmargin* is not None, then *xmargin* times the X data

lib/matplotlib/mpl-data/matplotlibrc

@@ -585,10 +585,14 @@
 #figure.constrained_layout.use: False  # When True, automatically make plot
                                        # elements fit on the figure. (Not
                                        # compatible with `autolayout`, above).
-#figure.constrained_layout.h_pad:  0.04167  # Padding around axes objects. Float representing
-#figure.constrained_layout.w_pad:  0.04167  # inches. Default is 3/72 inches (3 points)
-#figure.constrained_layout.hspace: 0.02     # Space between subplot groups. Float representing
-#figure.constrained_layout.wspace: 0.02     # a fraction of the subplot widths being separated.
+## Padding (in inches) around axes; defaults to 3/72 inches, i.e. 3 points.
+#figure.constrained_layout.h_pad:  0.04167
+#figure.constrained_layout.w_pad:  0.04167
+## Spacing between subplots, relative to the subplot sizes.  Much smaller than for
+## tight_layout (figure.subplot.hspace, figure.subplot.wspace) as constrained_layout
+## already takes surrounding texts (titles, labels, # ticklabels) into account.
+#figure.constrained_layout.hspace: 0.02
+#figure.constrained_layout.wspace: 0.02
 
 
 ## ***************************************************************************

lib/matplotlib/rcsetup.py

@@ -552,12 +552,12 @@ def validate_sketch(s):
         raise ValueError("Expected a (scale, length, randomness) triplet")
 
 
-def _validate_greaterequal0_lessthan1(s):
+def _validate_greaterthan_minushalf(s):
     s = validate_float(s)
-    if 0 <= s < 1:
+    if s > -0.5:
         return s
     else:
-        raise RuntimeError(f'Value must be >=0 and <1; got {s}')
+        raise RuntimeError(f'Value must be >-0.5; got {s}')
 
 
 def _validate_greaterequal0_lessequal1(s):
@@ -568,12 +568,6 @@ def _validate_greaterequal0_lessequal1(s):
         raise RuntimeError(f'Value must be >=0 and <=1; got {s}')
 
 
-_range_validators = {  # Slightly nicer (internal) API.
-    "0 <= x < 1": _validate_greaterequal0_lessthan1,
-    "0 <= x <= 1": _validate_greaterequal0_lessequal1,
-}
-
-
 def validate_hatch(s):
     r"""
     Validate a hatch pattern.
@@ -1012,9 +1006,9 @@ def _convert_validator_spec(key, conv):
     # If "data", axes limits are set close to the data.
     # If "round_numbers" axes limits are set to the nearest round numbers.
     "axes.autolimit_mode": ["data", "round_numbers"],
-    "axes.xmargin": _range_validators["0 <= x <= 1"],  # margin added to xaxis
-    "axes.ymargin": _range_validators["0 <= x <= 1"],  # margin added to yaxis
-    'axes.zmargin': _range_validators["0 <= x <= 1"],  # margin added to zaxis
+    "axes.xmargin": _validate_greaterthan_minushalf,  # margin added to xaxis
+    "axes.ymargin": _validate_greaterthan_minushalf,  # margin added to yaxis
+    "axes.zmargin": _validate_greaterthan_minushalf,  # margin added to zaxis
 
     "polaraxes.grid": validate_bool,  # display polar grid or not
     "axes3d.grid":    validate_bool,  # display 3d grid
@@ -1149,21 +1143,21 @@ def _convert_validator_spec(key, conv):
     "figure.max_open_warning": validate_int,
     "figure.raise_window":     validate_bool,
 
-    "figure.subplot.left":   _range_validators["0 <= x <= 1"],
-    "figure.subplot.right":  _range_validators["0 <= x <= 1"],
-    "figure.subplot.bottom": _range_validators["0 <= x <= 1"],
-    "figure.subplot.top":    _range_validators["0 <= x <= 1"],
-    "figure.subplot.wspace": _range_validators["0 <= x < 1"],
-    "figure.subplot.hspace": _range_validators["0 <= x < 1"],
+    "figure.subplot.left":   validate_float,
+    "figure.subplot.right":  validate_float,
+    "figure.subplot.bottom": validate_float,
+    "figure.subplot.top":    validate_float,
+    "figure.subplot.wspace": validate_float,
+    "figure.subplot.hspace": validate_float,
 
     "figure.constrained_layout.use": validate_bool,  # run constrained_layout?
     # wspace and hspace are fraction of adjacent subplots to use for space.
     # Much smaller than above because we don't need room for the text.
-    "figure.constrained_layout.hspace": _range_validators["0 <= x < 1"],
-    "figure.constrained_layout.wspace": _range_validators["0 <= x < 1"],
+    "figure.constrained_layout.hspace": validate_float,
+    "figure.constrained_layout.wspace": validate_float,
     # buffer around the axes, in inches.
-    'figure.constrained_layout.h_pad': validate_float,
-    'figure.constrained_layout.w_pad': validate_float,
+    "figure.constrained_layout.h_pad": validate_float,
+    "figure.constrained_layout.w_pad": validate_float,
 
     ## Saving figure's properties
     'savefig.dpi':          validate_dpi,
@@ -1207,7 +1201,7 @@ def _convert_validator_spec(key, conv):
     "docstring.hardcopy": validate_bool,
 
     "path.simplify":           validate_bool,
-    "path.simplify_threshold": _range_validators["0 <= x <= 1"],
+    "path.simplify_threshold": _validate_greaterequal0_lessequal1,
     "path.snap":               validate_bool,
     "path.sketch":             validate_sketch,
     "path.effects":            validate_anylist,