当xaxis是日期时间时如何在python图形上放置文本框

Question

I have made a figure with the x-axis as datetime (2012-8-1, 2012-10,7....)

I want to put a textbox to label this figure

id = ("(A)","(B)","(C)","(D)","(E)","(Average)")

X-axis

months = mpl.dates.MonthLocator() # every month
days = mpl.dates.DayLocator(interval=5) # every 10 days
dateFmt=mpl.dates.DateFormatter('%m-%d')    
ax.xaxis.set_major_formatter(dateFmt)
ax.xaxis.set_major_locator(months)
#ax.xaxis.set_minor_locator(days)
ax.xaxis_date()

Y-axis

ax.set_ylim(ymin[i],ymax[i])
ax.set_ylabel(ylabels)
ax.axhline(linewidth=0.5,color="k")
ax.yaxis.set_major_locator(tk.MaxNLocator(nbins=3))
ax.yaxis.set_minor_locator(tk.MaxNLocator(nbins=6))
[tickline.set_markersize(3) for tickline in ax.yaxis.get_ticklines(minor=True)]
[tickline.set_markersize(2.5) for tickline in ax.yaxis.get_ticklines(minor=True)]

Text

ax.text(0.25,ymax[i],id[i],fontsize=15)

But I can't see the labels at all.

How can I realize it?

Answer 1

You need to either enter the x-coordinate in the same format (a date) as for the other plot methods, or transform the coordinates. If you want to stick with the x=.25 you could use:

ax.text(0.25,ymax[i],id[i], transform=ax.transAxes, fontsize=15)

It will place the text at a quarter of the ax's width.

Answer 2

An approach is to convert the date to a number and use the number in subsequent calls:

dates = matplotlib.dates.date2num([x])
ax.text(dates[0], y, message, color='red')

where x is the datetime you want to convert, y is assumed not to be in datetime format but in numerical format, and message contains the string you want to have displayed.