Matplotlib: xticks every 15 minutes, starting on the hour

Question

I am trying to plot values of temperature against time with the time formatted as HH:MM. I am able to set the xticks to recur every 15 minutes but the first tick is at the first time (e.g. 04:40).

Is there a way to shift the ticks to occur on the hour and on the concurrent quarter-hours (04:45, 05:00, 05:15, etc.)? My current code is as follows:

import matplotlib.pyplot as plt
import matplotlib.dates as md
import datetime as dt

## Dummy times and temperatures
time = [dt.datetime(2017,2,15,4,40),dt.datetime(2017,2,15,4,46),dt.datetime(2017,2,15,4,52),dt.datetime(2017,2,15,4,58),dt.datetime(2017,2,15,5,4),dt.datetime(2017,2,15,5,10)]
temp = [7, 8, 9, 10, 11, 12]

## Plot the data
figtemp, ax = plt.subplots(1, 1)
ax.plot(time, temp)

## Set time format and the interval of ticks (every 15 minutes)
xformatter = md.DateFormatter('%H:%M')
xlocator = md.MinuteLocator(interval = 15)

## Set xtick labels to appear every 15 minutes
ax.xaxis.set_major_locator(xlocator)

## Format xtick labels as HH:MM
plt.gcf().axes[0].xaxis.set_major_formatter(xformatter)

Answer 1

You could tell the MinuteLocator to only use the minutes 0,15,30,45 using the byminute argument.

xlocator = md.MinuteLocator(byminute=[0,15,30,45], interval = 1)

Answer 2

Use Axes.set_xticklabels,

labels = ['04:45', '05:00', '05:15']
plt.gca().set_xticklabels(labels)

which produces,

---

Shift time to the concurrent quarter-hours,

import datetime

list_dt = [ datetime.datetime(2017,2,15,4,40),
            datetime.datetime(2017,2,15,4,46),
            datetime.datetime(2017,2,15,4,52),
            datetime.datetime(2017,2,15,4,58),
            datetime.datetime(2017,2,15,5,4),
            datetime.datetime(2017,2,15,5,10)]

adjust_list_dt = list()

for dt in list_dt:
    print(dt.minute//15)

    if dt.minute % 15 == 0:
        adjust_minutes = dt.minute
    else:
        adjust_minutes = (dt.minute//15 + 1)*15

    if adjust_minutes == 60:
        adjust_list_dt.append(dt.replace(hour=dt.hour+1, minute=0))
    else:
        adjust_list_dt.append(dt.replace(minute=adjust_minutes))

print(adjust_list_dt)
# Output
'''
[datetime.datetime(2017, 2, 15, 4, 45), 
 datetime.datetime(2017, 2, 15, 5, 0),
 datetime.datetime(2017, 2, 15, 5, 0), 
 datetime.datetime(2017, 2, 15, 5, 0), 
 datetime.datetime(2017, 2, 15, 5, 15), 
 datetime.datetime(2017, 2, 15, 5, 15)]
'''