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# Source code for pyqtgraph.widgets.ValueLabel

    from time import perf_counter

    from .. import functions as fn
    from ..Qt import QtWidgets

    __all__ = ['ValueLabel']

    class ValueLabel(QtWidgets.QLabel):
        """
        QLabel specifically for displaying numerical values.
        Extends QLabel adding some extra functionality:

          - displaying units with si prefix
          - built-in exponential averaging
        """

        def __init__(self, parent=None, suffix='', siPrefix=False, averageTime=0, formatStr=None, suffixPower=1):
            """
            ==============      ==================================================================================
            **Arguments:**
            suffix              (str or None) The suffix to place after the value
            siPrefix            (bool) Whether to add an SI prefix to the units and display a scaled value
            averageTime         (float) The length of time in seconds to average values. If this value
                                is 0, then no averaging is performed. As this value increases
                                the display value will appear to change more slowly and smoothly.
            formatStr           (str) Optionally, provide a format string to use when displaying text. The text
                                will be generated by calling formatStr.format(value=, avgValue=, suffix=)
                                (see Python documentation on str.format)
                                This option is not compatible with siPrefix
            suffixPower         (int/float) The power to which the suffix is raised. For example, if suffix='m²',
                                the suffixPower should be 2. This ensures correct scaling when using SI prefixes.
                                Supports positive, negative and non-integral powers. Ignored if siPrefix is False.
                                Note: The power only affects the scaling, not the suffix itself. For example, with
                                suffix='m' and suffixPower=2, the displayed suffix will still be 'm'.
            ==============      ==================================================================================
            """
            QtWidgets.QLabel.__init__(self, parent)
            self.values = []
            self.averageTime = averageTime ## no averaging by default
            self.suffix = suffix
            self.siPrefix = siPrefix
            if formatStr is None:
                formatStr = '{avgValue:0.2g} {suffix}'
            self.formatStr = formatStr
            self.suffixPower = suffixPower

        def setValue(self, value):
            now = perf_counter()
            self.values.append((now, value))
            cutoff = now - self.averageTime
            while len(self.values) > 0 and self.values[0][0] < cutoff:
                self.values.pop(0)
            self.update()

        def setFormatStr(self, text):
            self.formatStr = text
            self.update()

        def setAverageTime(self, t):
            self.averageTime = t

        def averageValue(self):
            return sum(v[1] for v in self.values) / float(len(self.values))

        def paintEvent(self, ev):
            self.setText(self.generateText())
            return super().paintEvent(ev)

        def generateText(self):
            if len(self.values) == 0:
                return ''
            avg = self.averageValue()
            val = self.values[-1][1]
            if self.siPrefix:
                return fn.siFormat(avg, suffix=self.suffix, power=self.suffixPower)
            else:
                return self.formatStr.format(value=val, avgValue=avg, suffix=self.suffix)