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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"A \"TypeError\" is raised if subclass inherited from \"datetime\" is used","articleBody":"Hello!\r\n\r\n**Bug summary**\r\n\r\nWhile trying to use `matplotlib` with custom subclass of `datetime` objects as x-values, a `TypeError` is raised.\r\n\r\nIt seems to exist a workaround using `matplotlib.units`: https://stackoverflow.com/a/10239347/2291710\r\n\r\nHowever, I would like to know is it could be possible or not to support any subclass inherited from `datetime` natively (using `issubclass()` for example)? I tried to dig into the `matplotlib` source code but this is too complex for me.\r\n\r\nThe main use-case is for users of alternative datetime libraries like `Pendulum` or `Arrow`.\r\n\r\n**Code for reproduction**\r\n\r\n\r\n```python\r\nimport datetime\r\nimport matplotlib.pyplot as plt\r\n\r\nclass MyDatetime(datetime.datetime):\r\n    pass\r\n\r\nvalues = range(4)\r\ndatetimes = [MyDatetime.now() for _ in values]\r\n\r\nfig, ax = plt.subplots()\r\nax.plot(datetimes, values)\r\n```\r\n\r\n**Actual outcome**\r\n\r\n```\r\nTraceback (most recent call last):\r\n  File \"C:\\Users\\delgan\\Desktop\\test.py\", line 11, in \u003cmodule\u003e\r\n    ax.plot(datetimes, values)\r\n  File \"C:\\Users\\delgan\\AppData\\Local\\Programs\\Python\\Python36\\lib\\site-packages\\matplotlib\\__init__.py\", line 1710, in inner\r\n    return func(ax, *args, **kwargs)\r\n  File \"C:\\Users\\delgan\\AppData\\Local\\Programs\\Python\\Python36\\lib\\site-packages\\matplotlib\\axes\\_axes.py\", line 1438, in plot\r\n    self.add_line(line)\r\n  File \"C:\\Users\\delgan\\AppData\\Local\\Programs\\Python\\Python36\\lib\\site-packages\\matplotlib\\axes\\_base.py\", line 1759, in add_line\r\n    self._update_line_limits(line)\r\n  File \"C:\\Users\\delgan\\AppData\\Local\\Programs\\Python\\Python36\\lib\\site-packages\\matplotlib\\axes\\_base.py\", line 1781, in _update_line_limits\r\n    path = line.get_path()\r\n  File \"C:\\Users\\delgan\\AppData\\Local\\Programs\\Python\\Python36\\lib\\site-packages\\matplotlib\\lines.py\", line 951, in get_path\r\n    self.recache()\r\n  File \"C:\\Users\\delgan\\AppData\\Local\\Programs\\Python\\Python36\\lib\\site-packages\\matplotlib\\lines.py\", line 652, in recache\r\n    x = _to_unmasked_float_array(xconv).ravel()\r\n  File \"C:\\Users\\delgan\\AppData\\Local\\Programs\\Python\\Python36\\lib\\site-packages\\matplotlib\\cbook\\__init__.py\", line 2008, in _to_unmasked_float_array\r\n    return np.asarray(x, float)\r\n  File \"C:\\Users\\delgan\\AppData\\Local\\Programs\\Python\\Python36\\lib\\site-packages\\numpy\\core\\numeric.py\", line 531, in asarray\r\n    return array(a, dtype, copy=False, order=order)\r\nTypeError: float() argument must be a string or a number, not 'MyDatetime'\r\n```\r\n\r\n**Expected outcome**\r\n\r\nThere should be no error, and the graph should be plotted as if the dates was proper `datetime` objects.\r\n\r\n**Matplotlib version**\r\n\u003c!--Please specify your platform and versions of the relevant libraries you are using:--\u003e\r\n  * Operating system: WSL\r\n  * Matplotlib version: 2.1.0\r\n  * Matplotlib backen: TkAgg\r\n  * Python version: 3.6.4\r\n","author":{"url":"https://github.com/Delgan","@type":"Person","name":"Delgan"},"datePublished":"2018-05-18T23:40:20.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/11275/matplotlib/issues/11275"}