Matplotlib ignoring timezone

Question

The following plot

import matplotlib
f= plt.figure(figsize=(12,4))
ax = f.add_subplot(111)
df.set_index('timestamp')['values'].plot(ax=ax)
ax.xaxis.set_major_locator(matplotlib.dates.HourLocator(interval=1))
ax.xaxis.set_major_formatter(matplotlib.dates.DateFormatter('%I'))
plt.show()

Renders the hour in the wrong zone (GMT) even though I have:

> df['timestamp'][0]
Timestamp('2014-09-02 18:37:00-0400', tz='US/Eastern')

As a matter of fact, if I comment out the line:

ax.xaxis.set_major_formatter(matplotlib.dates.DateFormatter('%I'))

the hour is rendered in the right time zone.

Why?

Answer 1

I think you can have the desired functionality by setting the timezone in rcParams:

import matplotlib
matplotlib.rcParams['timezone'] = 'US/Eastern'

The formatter is timezone aware and will convert the timestamp to your rcParams timezone (which is probably at UTC), while if you don't format it, it will just take the timestamp and ignore the timezone. If I understand correctly.

More reading:

• Matplotlib dates
• A related answer

Answer 2

If you don't want to change rcParams (which seems to be an easy fix), then you can pass the timezone to mdates.DateFormatter.

from dateutil import tz
mdates.DateFormatter('%H:%M', tz=tz.gettz('Europe/Berlin'))

The problem is that mdates.DateFormatter completely ignores everything you set in like plot_date or xaxis_date or whatever you use.