improve legend docstring

timhoffm · timhoffm · commit 4776e50f245e · 2017-12-17T22:40:06.000+01:00
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -283,38 +283,83 @@ def legend(self, *args, **kwargs):
         """
         Places a legend on the axes.
 
-        To make a legend for lines which already exist on the axes
-        (via plot for instance), simply call this function with an iterable
-        of strings, one for each legend item. For example::
+        Call signatures::
 
-            ax.plot([1, 2, 3])
-            ax.legend(['A simple line'])
+            legend()
+            legend(labels)
+            legend(handles, labels)
+
+        The call signatures correspond to three different ways how to use
+        this method.
 
-        However, in order to keep the "label" and the legend element
-        instance together, it is preferable to specify the label either at
-        artist creation, or by calling the
-        :meth:`~matplotlib.artist.Artist.set_label` method on the artist::
+        **1. Automatic detection of elements to be shown in the legend**
+
+        The elements to be added to the legend are automatically determined,
+        when you do not pass in any extra arguments.
+
+        In this case, the labels are taken from the artist. You can specify
+        them either at artist creation or by calling the
+        :meth:`~.Artist.set_label` method on the artist::
 
             line, = ax.plot([1, 2, 3], label='Inline label')
-            # Overwrite the label by calling the method.
+            ax.legend()
+
+        or::
+
             line.set_label('Label via method')
+            line, = ax.plot([1, 2, 3])
             ax.legend()
 
         Specific lines can be excluded from the automatic legend element
         selection by defining a label starting with an underscore.
-        This is default for all artists, so calling :meth:`legend` without
+        This is default for all artists, so calling `Axes.legend` without
         any arguments and without setting the labels manually will result in
         no legend being drawn.
 
+
+        **2. Labeling existing plot elements**
+
+        To make a legend for lines which already exist on the axes
+        (via plot for instance), simply call this function with an iterable
+        of strings, one for each legend item. For example::
+
+            ax.plot([1, 2, 3])
+            ax.legend(['A simple line'])
+
+        Note: This way of using is discouraged, because the relation between
+        plot elements and labels is only implicit by their order and can
+        easily be mixed up.
+
+
+        **3. Explicitly defining the elements in the legend**
+
         For full control of which artists have a legend entry, it is possible
         to pass an iterable of legend artists followed by an iterable of
         legend labels respectively::
 
-           legend((line1, line2, line3), ('label1', 'label2', 'label3'))
+            legend((line1, line2, line3), ('label1', 'label2', 'label3'))
 
         Parameters
         ----------
 
+        handles : sequence of `~.Artist`, optional
+            A list of Artists (lines, patches) to be added to the legend.
+            Use this together with *labels*, if you need full control on what
+            is shown in the legend and the automatic mechanism described above
+            is not sufficient.
+
+            The length of handles and labels should be the same in this
+            case. If they are not, they are truncated to the smaller length.
+
+        labels : sequence of strings, optional
+            A list of labels to show next to the artists.
+            Use this together with *handles*, if you need full control on what
+            is shown in the legend and the automatic mechanism described above
+            is not sufficient.
+
+        Other Parameters
+        ----------------
+
         loc : int or string or pair of floats, default: 'upper right'
             The location of the legend. Possible codes are:
 
diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
@@ -1373,6 +1373,24 @@ def legend(self, *args, **kwargs):
         Parameters
         ----------
 
+        handles : sequence of `~.Artist`, optional
+            A list of Artists (lines, patches) to be added to the legend.
+            Use this together with *labels*, if you need full control on what
+            is shown in the legend and the automatic mechanism described above
+            is not sufficient.
+
+            The length of handles and labels should be the same in this
+            case. If they are not, they are truncated to the smaller length.
+
+        labels : sequence of strings, optional
+            A list of labels to show next to the artists.
+            Use this together with *handles*, if you need full control on what
+            is shown in the legend and the automatic mechanism described above
+            is not sufficient.
+
+        Other Parameters
+        ----------------
+
         loc : int or string or pair of floats, default: 'upper right'
             The location of the legend. Possible codes are:
 
diff --git a/lib/matplotlib/legend.py b/lib/matplotlib/legend.py
@@ -286,9 +286,7 @@ def _update_bbox_to_anchor(self, loc_in_canvas):
 
 class Legend(Artist):
     """
-    Place a legend on the axes at location loc.  Labels are a
-    sequence of strings and loc can be a string or an integer
-    specifying the legend location
+    Place a legend on the axes at location loc.
 
     """
     codes = {'best':         0,  # only implemented for axes legends
@@ -353,13 +351,22 @@ def __init__(self, parent, handles, labels,
                  handler_map=None,
                  ):
         """
-        - *parent*: the artist that contains the legend
-        - *handles*: a list of artists (lines, patches) to be added to the
-                      legend
-        - *labels*: a list of strings to label the legend
 
         Parameters
         ----------
+        parent : `.Axes` or `.Figure`
+            The artist that contains the legend.
+
+        handles : sequence of `.Artist`
+            A list of Artists (lines, patches) to be added to the legend.
+
+        labels : sequence of strings
+            A list of labels to show next to the artists. The length of handles
+            and labels should be the same. If they are not, they are truncated
+            to the smaller of both lengths.
+
+        Other Parameters
+        ----------------
 
         loc : int or string or pair of floats, default: 'upper right'
             The location of the legend. Possible codes are:
diff --git a/lib/matplotlib/pyplot.py b/lib/matplotlib/pyplot.py
@@ -283,8 +283,8 @@ def pause(interval):
     This can be used for crude animation.  For more complex animation, see
     :mod:`matplotlib.animation`.
 
-    Note
-    ----
+    Notes
+    -----
     This function is experimental; its behavior may be changed or extended in a
     future release.
     """
diff --git a/lib/matplotlib/tests/test_legend.py b/lib/matplotlib/tests/test_legend.py
@@ -40,9 +40,14 @@ def get_docstring_section(func, section):
 
 
 def test_legend_kwdocstrings():
-    stleg = get_docstring_section(mpl.legend.Legend.__init__, 'Parameters')
     stax = get_docstring_section(mpl.axes.Axes.legend, 'Parameters')
     stfig = get_docstring_section(mpl.figure.Figure.legend, 'Parameters')
+    assert stfig == stax
+
+    stleg = get_docstring_section(mpl.legend.Legend.__init__,
+                                  'Other Parameters')
+    stax = get_docstring_section(mpl.axes.Axes.legend, 'Other Parameters')
+    stfig = get_docstring_section(mpl.figure.Figure.legend, 'Other Parameters')
     assert stleg == stax
     assert stfig == stax
     assert stleg == stfig
