Copy `DateFormatter` from matplotlib

https://github.com/matplotlib/matplotlib/blob/d5210e4a87665581205f5147703dbd229b44cf66/lib/matplotlib/dates.py#L627-L655

plot_statistics.py

@@ -44,6 +44,36 @@ axesColors = ['blue', 'green', 'brown', 'orange', 'brown', 'red', 'purple']
 axesLabels = ['targets', 'compressed blockchain size (in blocks)', 'compressed blockchain score', 'constant difficulty compressed blockchain size (in blocks)', 'constant difficulty compressed blockchain score', 'compressed blockchain size keeping all blocks since last m higher block (in blocks)', 'compressed blockchain score keeping all blocks since last m higher block']
 axesYValues = [targets, data['compressSize'], data['compressScore'], dataConstantDifficulty['compressSize'], dataConstantDifficulty['compressScore'], dataKeepingAllBlocksSinceLastMHigherBlock['compressSize'], dataKeepingAllBlocksSinceLastMHigherBlock['compressScore']]
 
+class DateFormatter(ticker.Formatter):
+    """
+    Format a tick (in days since the epoch) with a
+    `~datetime.datetime.strftime` format string.
+    """
+
+    def __init__(self, fmt, tz=None, *, usetex=None):
+        """
+        Parameters
+        ----------
+        fmt : str
+            `~datetime.datetime.strftime` format string
+        tz : str or `~datetime.tzinfo`, default: :rc:`timezone`
+            Ticks timezone. If a string, *tz* is passed to `dateutil.tz`.
+        usetex : bool, default: :rc:`text.usetex`
+            To enable/disable the use of TeX's math mode for rendering the
+            results of the formatter.
+        """
+        self.tz = _get_tzinfo(tz)
+        self.fmt = fmt
+        self._usetex = (usetex if usetex is not None else
+                        mpl.rcParams['text.usetex'])
+
+    def __call__(self, x, pos=0):
+        result = num2date(x, self.tz).strftime(self.fmt)
+        return _wrap_in_tex(result) if self._usetex else result
+
+    def set_tzinfo(self, tz):
+        self.tz = _get_tzinfo(tz)
+
 plt.gca().xaxis.set_major_formatter(mdates.DateFormatter('%m/%Y'))
 
 curves = []
@@ -70,7 +100,7 @@ curves.insert(-2, legendNewLine[0])
 curves += legendNewLine + targetRecomputationCurve + [firstTargetDecreaseCurve] + [targetIncreaseCurve]
 labels = [curve.get_label() for curve in curves]
 
-plt.legend(curves, labels, loc='upper center', framealpha=1, bbox_to_anchor=(0.5, -0.125))
+#plt.legend(curves, labels, loc='upper center', framealpha=1, bbox_to_anchor=(0.5, -0.125))
 
 targetsAxis.set_xlabel('Block height')