matplotlib how to specify time locator's start-ticking timestamp?

Question

All I want is quite straight forward, I just want the locator ticks to start at a specified timestamp:
peudo code: locator.set_start_ticking_at( datetime_dummy )

Answer 1

@unutbu: Many thanks: I've been looking everywhere for the answer to a related problem!

@eliu: I've adapted unutbu's excellent answer to demonstrate how you can define lists (to create different 'dateutil' rules) which give you complete control over which x-ticks are displayed. Try un-commenting each example below in turn and play around with the values to see the effect. Hope this helps.

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.dates as mdates

idx = pd.date_range('2017-01-01 05:03', '2017-01-01 18:03', freq = 'min')
df = pd.Series(np.random.randn(len(idx)),  index = idx)
fig, ax = plt.subplots()

# Choose which major hour ticks are displayed by creating a 'dateutil' rule e.g.:

# Only use the hours in an explicit list:
# hourlocator = mdates.HourLocator(byhour=[6,12,8])

# Use the hours in a range defined by: Start, Stop, Step:
# hourlocator = mdates.HourLocator(byhour=range(8,15,2))

# Use every 3rd hour:
# hourlocator = mdates.HourLocator(interval = 3)

# Set the format of the major x-ticks:
majorFmt = mdates.DateFormatter('%H:%M')  

ax.xaxis.set_major_locator(hourlocator)
ax.xaxis.set_major_formatter(majorFmt)

#... and ditto to set minor_locators and minor_formatters for minor x-ticks if needed as well)

ax.plot(df.index, df.values, color = 'black', linewidth = 0.4)

fig.autofmt_xdate() # optional: makes 30 deg tilt on tick labels

plt.show()