Issue251 help matplotlib load times (#255)

* add controls to subplot

* convert plot() so that it can be called more than once to show Metrics on the same graph

* moved plot() call into it's own file and more importantly, made the loading of matplotlib lazy loaded only on plot() call. Also added some additional code as a direction for later

Author: mahtin

prometheus_api_client/metric.py

@@ -5,16 +5,6 @@
 
 from prometheus_api_client.exceptions import MetricValueConversionError
 
-try:
-    import matplotlib.pyplot as plt
-    from pandas.plotting import register_matplotlib_converters
-
-    register_matplotlib_converters()
-    _MPL_FOUND = True
-except ImportError as exce:  # noqa F841
-    _MPL_FOUND = False
-
-
 class Metric:
     r"""
     A Class for `Metric` object.
@@ -91,6 +81,9 @@ def __init__(self, metric, oldest_data_datetime=None):
         self.start_time = self.metric_values.iloc[0, 0]
         self.end_time = self.metric_values.iloc[-1, 0]
 
+        # We store the plot information as Class variable
+        Metric._plot = None
+
     def __eq__(self, other):
         """
         Overloading operator ``=``.
@@ -187,12 +180,19 @@ def __add__(self, other):
             error_string = "Different metric labels"
         raise TypeError("Cannot Add different metric types. " + error_string)
 
-    def plot(self):
+    _metric_plot = None
+
+    def plot(self, *args, **kwargs):
         """Plot a very simple line graph for the metric time-series."""
-        if _MPL_FOUND:
-            fig, axis = plt.subplots()
-            axis.plot_date(self.metric_values.ds, self.metric_values.y, linestyle=":")
-            fig.autofmt_xdate()
-        # if matplotlib was not imported
-        else:
-            raise ImportError("matplotlib was not found")
+        if not Metric._metric_plot:
+            from prometheus_api_client.metric_plot import MetricPlot
+            Metric._metric_plot = MetricPlot(*args, **kwargs)
+        metric = self
+        Metric._metric_plot.plot_date(metric)
+
+    def show(self, block=None):
+        """Plot a very simple line graph for the metric time-series."""
+        if not Metric._metric_plot:
+            # can't show before plot
+            TypeError("Invalid operation: Can't show() before plot()")
+        Metric._metric_plot.show(block)

prometheus_api_client/metric_plot.py

@@ -0,0 +1,65 @@
+"""plot code for metric class."""
+
+# This only gets called if there's a plot() call
+# This speeds up load time for all the non plot() users
+#
+# Only loads matplotlib etc during __init__
+#
+
+class MetricPlot:
+    r"""
+    A Class for `MetricPlot` object.
+
+    Internal use only at present
+
+    """
+
+    def __init__(self, *args, **kwargs):
+        """Functions as a Constructor for the Metric object."""
+        try:
+            import matplotlib.pyplot as plt
+            from pandas.plotting import register_matplotlib_converters
+
+            register_matplotlib_converters()
+        except ImportError as exce:  # noqa F841
+            raise ImportError("matplotlib was not found")
+
+        # One graph with potentially N lines - if plot() is called twice
+        self._plt = plt
+        self._fig, self._axis = self._plt.subplots(*args, **kwargs)
+
+    def plot_date(self, metric):
+        """Plot a very simple line graph for the metric time-series."""
+
+        # If we made it here, then we know matplotlib is installed and available
+        self._axis.plot_date(metric.metric_values.ds, metric.metric_values.y,
+            linestyle="solid",
+            label=str(metric.metric_name),
+        )
+        self._fig.autofmt_xdate()
+        # These are provided for documentation reasons only - it's presumptuous for this code to call them
+        # self._axis.set_xlabel('Date/Time')
+        # self._axis.set_ylabel('Metric')
+        # self._axis.set_title('Prometheus')
+        if len(self._axis.lines) > 1:
+            # We show a legend (or update the legend) if there's more than line on the plot
+            self._axis.legend()
+
+    def show(self, block=None):
+        """convience show() call."""
+        self._plt.show(block=block)
+
+    @property
+    def plt(self):
+        """ pyplot value for present plotting """
+        return self._plt
+
+    @property
+    def axis(self):
+        """ Axis value for present plotting """
+        return self._axis
+
+    @property
+    def fig(self):
+        """ Figure value for present plotting """
+        return self._fig