Simple implementation of TimeAxisItem and test program

TimePlot.py

from pyqtgraph.Qt import QtGui, QtCore
import numpy as np
import pyqtgraph as pg
from PySide.QtCore import QTime, QTimer
from collections import deque

t = QTime()
t.start()
data = deque(maxlen=20)

class TimeAxisItem(pg.AxisItem):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

    def tickStrings(self, values, scale, spacing):
        # PySide's QTime() initialiser fails miserably and dismisses args/kwargs
        return [QTime().addMSecs(value).toString('mm:ss') for value in values]




app = QtGui.QApplication([])

win = pg.GraphicsWindow(title="Basic plotting examples")
win.resize(1000,600)

plot = win.addPlot(title='Timed data', axisItems={'bottom': TimeAxisItem(orientation='bottom')})
curve = plot.plot()

def update():
    global plot, curve, data
    data.append({'x': t.elapsed(), 'y': np.random.randint(0, 100)})
    x = [item['x'] for item in data]
    y = [item['y'] for item in data]
    curve.setData(x=x, y=y)

tmr = QTimer()
tmr.timeout.connect(update)
tmr.start(800)

if __name__ == '__main__':
    import sys
    if (sys.flags.interactive != 1) or not hasattr(QtCore, 'PYQT_VERSION'):
        QtGui.QApplication.instance().exec_()

Same code with PyQt4 but without global variables

    import sys
    import numpy as np
    from pyqtgraph.Qt import QtGui, QtCore
    import pyqtgraph as pg
    from PyQt4.QtCore import QTime, QTimer
    from collections import deque

    class TimeAxisItem(pg.AxisItem):
        def __init__(self, *args, **kwargs):
            super().__init__(*args, **kwargs)

        def tickStrings(self, values, scale, spacing):
            # PySide's QTime() initialiser fails miserably and dismisses args/kwargs
            return [QTime().addMSecs(value).toString('mm:ss') for value in values]

    class MyApplication(QtGui.QApplication):
        def __init__(self, *args, **kwargs):
            super(MyApplication, self).__init__(*args, **kwargs)
            self.t = QTime()
            self.t.start()

            self.data = deque(maxlen=20)

            self.win = pg.GraphicsWindow(title="Basic plotting examples")
            self.win.resize(1000,600)

            self.plot = self.win.addPlot(title='Timed data', axisItems={'bottom': TimeAxisItem(orientation='bottom')})
            self.curve = self.plot.plot()

            self.tmr = QTimer()
            self.tmr.timeout.connect(self.update)
            self.tmr.start(100)

        def update(self):
            self.data.append({'x': self.t.elapsed(), 'y': np.random.randint(0, 100)})
            x = [item['x'] for item in self.data]
            y = [item['y'] for item in self.data]
            self.curve.setData(x=x, y=y)

    def main():
        app = MyApplication(sys.argv)
        sys.exit(app.exec_())

    if __name__ == '__main__':
        main()

A random walk example with datetime as x axis:

import sys
import numpy as np
import datetime

from PyQt4.QtCore import QTime, QTimer
from pyqtgraph.Qt import QtGui, QtCore
import pyqtgraph as pg

from collections import deque

import pytz
UNIX_EPOCH_naive = datetime.datetime(1970, 1, 1, 0, 0) #offset-naive datetime
UNIX_EPOCH_offset_aware = datetime.datetime(1970, 1, 1, 0, 0, tzinfo = pytz.utc) #offset-aware datetime
UNIX_EPOCH = UNIX_EPOCH_naive

TS_MULT_us = 1e6

def now_timestamp(ts_mult=TS_MULT_us, epoch=UNIX_EPOCH):
    return(int((datetime.datetime.utcnow() - epoch).total_seconds()*ts_mult))

def int2dt(ts, ts_mult=TS_MULT_us):
    return(datetime.datetime.utcfromtimestamp(float(ts)/ts_mult))

def dt2int(dt, ts_mult=TS_MULT_us, epoch=UNIX_EPOCH):
    delta = dt - epoch
    return(int(delta.total_seconds()*ts_mult))

def td2int(td, ts_mult=TS_MULT_us):
    return(int(td.total_seconds()*ts_mult))

def int2td(ts, ts_mult=TS_MULT_us):
    return(datetime.timedelta(seconds=float(ts)/ts_mult))

class TimeAxisItem(pg.AxisItem):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

    def tickStrings(self, values, scale, spacing):
        # PySide's QTime() initialiser fails miserably and dismisses args/kwargs
        #return [QTime().addMSecs(value).toString('mm:ss') for value in values]
        return [int2dt(value).strftime("%H:%M:%S.%f") for value in values]

class MyApplication(QtGui.QApplication):
    def __init__(self, *args, **kwargs):
        super(MyApplication, self).__init__(*args, **kwargs)
        self.t = QTime()
        self.t.start()

        maxlen = 200
        self.data_x = deque(maxlen=maxlen)
        self.data_y = deque(maxlen=maxlen)

        self.win = pg.GraphicsWindow(title="Basic plotting examples")
        self.win.resize(1000,600)

        self.plot = self.win.addPlot(title='Timed data', axisItems={'bottom': TimeAxisItem(orientation='bottom')})
        #self.plot.setYRange(0, 150)
        self.curve = self.plot.plot()

        self.tmr = QTimer()
        self.tmr.timeout.connect(self.update)
        self.tmr.start(100)

        self.y = 100

    def update(self):
        #self.data.append({'x': self.t.elapsed(), 'y': np.random.randint(0, 100)})
        x = now_timestamp()
        self.y = self.y + np.random.uniform(-1, 1)

        self.data_x.append(x)
        self.data_y.append(self.y)
        self.curve.setData(x=list(self.data_x), y=list(self.data_y))

def main():
    app = MyApplication(sys.argv)
    sys.exit(app.exec_())

if __name__ == '__main__':
    main()

wonderful as @scls19fr wrote.Thx

fix to work with Python 2.7.12

import sys
import numpy as np
import datetime

from PyQt4.QtCore import QTime, QTimer
from pyqtgraph.Qt import QtGui, QtCore
import pyqtgraph as pg

from collections import deque

import pytz
UNIX_EPOCH_naive = datetime.datetime(1970, 1, 1, 0, 0) #offset-naive datetime
UNIX_EPOCH_offset_aware = datetime.datetime(1970, 1, 1, 0, 0, tzinfo = pytz.utc) #offset-aware datetime
UNIX_EPOCH = UNIX_EPOCH_naive

TS_MULT_us = 1e6

def now_timestamp(ts_mult=TS_MULT_us, epoch=UNIX_EPOCH):
    return(int((datetime.datetime.utcnow() - epoch).total_seconds()*ts_mult))

def int2dt(ts, ts_mult=TS_MULT_us):
    return(datetime.datetime.utcfromtimestamp(float(ts)/ts_mult))

def dt2int(dt, ts_mult=TS_MULT_us, epoch=UNIX_EPOCH):
    delta = dt - epoch
    return(int(delta.total_seconds()*ts_mult))

def td2int(td, ts_mult=TS_MULT_us):
    return(int(td.total_seconds()*ts_mult))

def int2td(ts, ts_mult=TS_MULT_us):
    return(datetime.timedelta(seconds=float(ts)/ts_mult))

class TimeAxisItem(pg.AxisItem):
    def __init__(self, *args, **kwargs):
        #  super().__init__(*args, **kwargs)
        super(TimeAxisItem, self).__init__(*args, **kwargs)

    def tickStrings(self, values, scale, spacing):
        # PySide's QTime() initialiser fails miserably and dismisses args/kwargs
        #return [QTime().addMSecs(value).toString('mm:ss') for value in values]
        return [int2dt(value).strftime("%H:%M:%S.%f") for value in values]

class MyApplication(QtGui.QApplication):
    def __init__(self, *args, **kwargs):
        super(MyApplication, self).__init__(*args, **kwargs)
        self.t = QTime()
        self.t.start()

        maxlen = 200
        self.data_x = deque(maxlen=maxlen)
        self.data_y = deque(maxlen=maxlen)

        self.win = pg.GraphicsWindow(title="Basic plotting examples")
        self.win.resize(1000,600)

        tai = TimeAxisItem(orientation='bottom')
        self.plot = self.win.addPlot(title='Timed data', axisItems={'bottom': TimeAxisItem(orientation='bottom')})
        #self.plot.setYRange(0, 150)
        self.curve = self.plot.plot()

        self.tmr = QTimer()
        self.tmr.timeout.connect(self.update)
        self.tmr.start(100)

        self.y = 100

    def update(self):
        #self.data.append({'x': self.t.elapsed(), 'y': np.random.randint(0, 100)})
        x = now_timestamp()
        self.y = self.y + np.random.uniform(-1, 1)

        self.data_x.append(x)
        self.data_y.append(self.y)
        self.curve.setData(x=list(self.data_x), y=list(self.data_y))

def main():
    app = MyApplication(sys.argv)
    sys.exit(app.exec_())

if __name__ == '__main__':
    main()

Thanks a lot for these sample…
For my need with only seconds and not utc but France local time, and python 3.6.1 :

class TimeAxisItem(pg.AxisItem):
    def __init__(self, *args, **kwargs):
        super(TimeAxisItem, self).__init__(*args, **kwargs)

    def tickStrings(self, values, scale, spacing):
        return [int2dt(value).strftime("%Hh%Mmn%Ss") for value in values]

def now_timestamp():
    return int(time.time())

def int2dt(ts):
    if not ts:
        return datetime.datetime.utcfromtimestamp(ts) # workaround fromtimestamp bug (1)
    return(datetime.datetime.fromtimestamp(ts))

…
(1) https://github.com/home-assistant/appdaemon/issues/83!