Date tick labels

Show how to make date plots in Matplotlib using date tick locators and formatters. See Major and minor ticks for more information on controlling major and minor ticks.

All matplotlib date plotting is done by converting date instances into days since 0001-01-01 00:00:00 UTC plus one day (for historical reasons). The conversion, tick locating and formatting is done behind the scenes so this is most transparent to you. The dates module provides several converter functions matplotlib.dates.date2num and matplotlib.dates.num2date. These can convert between datetime.datetime objects and numpy.datetime64 objects.

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.dates as mdates
import matplotlib.cbook as cbook

years = mdates.YearLocator()   # every year
months = mdates.MonthLocator()  # every month
years_fmt = mdates.DateFormatter('%Y')

# Load a numpy structured array from yahoo csv data with fields date, open,
# close, volume, adj_close from the mpl-data/example directory.  This array
# stores the date as an np.datetime64 with a day unit ('D') in the 'date'
# column.
with cbook.get_sample_data('goog.npz') as datafile:
    data = np.load(datafile)['price_data']

fig, ax = plt.subplots()
ax.plot('date', 'adj_close', data=data)

# format the ticks
ax.xaxis.set_major_locator(years)
ax.xaxis.set_major_formatter(years_fmt)
ax.xaxis.set_minor_locator(months)

# round to nearest years.
datemin = np.datetime64(data['date'][0], 'Y')
datemax = np.datetime64(data['date'][-1], 'Y') + np.timedelta64(1, 'Y')
ax.set_xlim(datemin, datemax)

# format the coords message box
ax.format_xdata = mdates.DateFormatter('%Y-%m-%d')
ax.format_ydata = lambda x: '$%1.2f' % x  # format the price.
ax.grid(True)

# rotates and right aligns the x labels, and moves the bottom of the
# axes up to make room for them
fig.autofmt_xdate()

plt.show()