Pygal plots involving datetime throw error with dates prior to 1970

Question

Trying out the sample code for an XY plot in pygal involving datetime or date, any dates prior to 1970 cause this traceback:

Traceback (most recent call last):
  File "C:/Users/***/dt_test.py", line 30, in <module>
    datetimeline.render()
  File "C:\Python\Python36\lib\site-packages\pygal\graph\public.py", line 52, 
in render
    self.setup(**kwargs)
  File "C:\Python\Python36\lib\site-packages\pygal\graph\base.py", line 217, 
in setup
self._draw()
  File "C:\Python\Python36\lib\site-packages\pygal\graph\graph.py", line 924, 
in _draw
    self._compute_x_labels()
  File "C:\Python\Python36\lib\site-packages\pygal\graph\dual.py", line 61, 
in _compute_x_labels
    self._x_labels = list(zip(map(self._x_format, x_pos), x_pos))
  File "C:\Python\Python36\lib\site-packages\pygal\graph\time.py", line 103, 
in datetime_to_str
    dt = datetime.utcfromtimestamp(x)
OSError: [Errno 22] Invalid argument

Does anyone else get this behavior? (I'm using PyCharm.) lPerhaps the 'millennium' is returning an unexpected negative number?

(Edit) I used the code under "date", running in PyCharm:

from datetime import datetime
datetimeline = pygal.DateTimeLine(
    x_label_rotation=35, truncate_label=-1,
    x_value_formatter=lambda dt: dt.strftime('%d, %b %Y at %I:%M:%S %p'))
datetimeline.add("Serie", [
    (datetime(2013, 1, 2, 12, 0), 300),
    (datetime(2013, 1, 12, 14, 30, 45), 412),
    (datetime(2013, 2, 2, 6), 823),
    (datetime(2013, 2, 22, 9, 45), 672)
])
datetimeline.render()

... when I change the '2013' to '1969,' I get the Traceback shown above.

Can you show us your code and the time you used? I tried to change "2013" to "1969" and I was able to plot the data. — TYZ, Mar 23 '18 at 17:56

score 1 · Accepted Answer · answered Jun 22 '18 at 19:41

This is caused by limitations in the underlying C functions that python uses for some date and time handling. These functions are implemented differently on different platforms, which is why it doesn't affect everybody (I had to borrow a Windows box to replicate the error).

The docs for datetime.utcfromtimestamp mention these limitations:

This may raise OverflowError, if the timestamp is out of the range of values supported by the platform C gmtime() function, and OSError on gmtime() failure. It’s common for this to be restricted to years in 1970 through 2038.

Fortunately the same docs suggest a workaround, and, as the function in the DateTimeLine class that contains the troublesome line is so short we can easily create our own class that inherits from DateTimeLine and over-rides the function.

import pygal
from datetime import datetime, timedelta, timezone

class MyDateTimeLine(pygal.DateTimeLine):

    @property
    def _x_format(self):
        def datetime_to_str(x):
            dt = datetime(1970, 1, 1, tzinfo=timezone.utc) + timedelta(seconds=x)
            return self.x_value_formatter(dt)
        return datetime_to_str

This is pretty much just copied from the source code for DateTimeLine. The only change is to the line assigning a value to dt.

We can now use this class as a drop-in replacement for DateTimeLine to plot dates in 2013 or 1969:

formatter = lambda dt: dt.strftime("%d, %b %Y at %I:%M:%S %p")

chart = MyDateTimeLine(x_label_rotation=35, truncate_label=-1,
                       x_value_formatter=formatter, width=640, height=300)
chart.add("2013", [(datetime(2013, 1, 2, 12, 0), 300),
                   (datetime(2013, 1, 12, 14, 30, 45), 412),
                   (datetime(2013, 2, 2, 6), 823),
                   (datetime(2013, 2, 22, 9, 45), 672)])
chart.render_to_png("chart2013.png")

chart = MyDateTimeLine(x_label_rotation=35, truncate_label=-1,
                       x_value_formatter=formatter, width=640, height=300)
chart.add("1969", [(datetime(1969, 1, 2, 12, 0), 300),
                   (datetime(1969, 1, 12, 14, 30, 45), 412),
                   (datetime(1969, 2, 2, 6), 823),
                   (datetime(1969, 2, 22, 9, 45), 672)])
chart.render_to_png("chart1969.png")

Pygal plots involving datetime throw error with dates prior to 1970

1 Answers1