如何使用PyQtGraph的DateAxisItem？

Question

我在Python 3.6.2（32位）和Windows 10上使用PyQtGraph'0.9.8 + gd627e39'。

我的目标是使用显示日期时间的X轴绘制实时数据。

Time                                                Value
datetime.datetime(2018, 3, 1, 9, 36, 50, 136415)    10
datetime.datetime(2018, 3, 1, 9, 36, 51, 330912)    9
datetime.datetime(2018, 3, 1, 9, 36, 51, 382815)    12
datetime.datetime(2018, 3, 1, 9, 36, 52, 928818)    11
...

我查了一些相关的问题，比如 https://gist.github.com/friendzis/4e98ebe2cf29c0c2c232，pyqtgraph, plotting time series，但我仍然很难掌握如何使用DateAxisItem

我尝试使用模块制作一个简单的代码，

import numpy as np
import pyqtgraph as pg
from pyqtgraph.Qt import QtCore, QtGui
from datetime import datetime
from time import time

t1 = datetime.now()
t2 = datetime.now()

list_x = [ t1, t2 ]
list_y = [ 0, 1 ]

date_axis = pg.graphicsItems.DateAxisItem.DateAxisItem(orientation = 'bottom')
graph = pg.PlotWidget(axisItems = {'bottom': date_axis})

graph.plot(x=list_x, y=list_y, pen=None, symbol='o')
graph.show()

但它显示错误消息，并且根本不显示其X轴。

Traceback (most recent call last):
File "<tmp 10>", line 19, in <module>
    graph.plot(x=list_x, y=list_y, pen=None, symbol='o')
File "d:\python36-32\lib\site-packages\pyqtgraph\graphicsItems\PlotItem\PlotItem.py", line 636, in plot
    item = PlotDataItem(*args, **kargs)
File "d:\python36-32\lib\site-packages\pyqtgraph\graphicsItems\PlotDataItem.py", line 177, in __init__
    self.setData(*args, **kargs)
File "d:\python36-32\lib\site-packages\pyqtgraph\graphicsItems\PlotDataItem.py", line 461, in setData
    self.updateItems()
File "d:\python36-32\lib\site-packages\pyqtgraph\graphicsItems\PlotDataItem.py", line 493, in updateItems
    self.scatter.setData(x=x, y=y, **scatterArgs)
File "d:\python36-32\lib\site-packages\pyqtgraph\graphicsItems\ScatterPlotItem.py", line 308, in setData
    self.addPoints(*args, **kargs)
File "d:\python36-32\lib\site-packages\pyqtgraph\graphicsItems\ScatterPlotItem.py", line 388, in addPoints
    newData['x'] = kargs['x']
TypeError: float() argument must be a string or a number, not 'datetime.datetime'

是因为DateAxisItem不支持日期时间吗？如果我能通过查看代码来理解模块，那将是很棒的，但不幸的是，我的技能并不好。

如果有人能告诉我如何将模块与一些简单的数据一起使用，我会很感激。

Answer 1

基于之前的answer，pyqtgraph中的绘图只接受数字类型的数据，因此您必须对其进行转换，在这种情况下，我们使用timestamp()，然后在自定义AxisItem中将其转换为字符串，以便在fromtimestamp的帮助下显示它。

import numpy as np
import pyqtgraph as pg
from pyqtgraph.Qt import QtCore, QtGui
from datetime import datetime


class TimeAxisItem(pg.AxisItem):
    def tickStrings(self, values, scale, spacing):
        return [datetime.fromtimestamp(value) for value in values]

list_x = [datetime(2018, 3, 1, 9, 36, 50, 136415), 
        datetime(2018, 3, 1, 9, 36, 51, 330912),
        datetime(2018, 3, 1, 9, 36, 51, 382815),
        datetime(2018, 3, 1, 9, 36, 52, 928818)]

list_y = [10, 9, 12, 11]

app = QtGui.QApplication([])

date_axis = TimeAxisItem(orientation='bottom')
graph = pg.PlotWidget(axisItems = {'bottom': date_axis})

graph.plot(x=[x.timestamp() for x in list_x], y=list_y, pen=None, symbol='o')
graph.show()

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