Adding arrows to mpf finance plots

I am trying to add an arrow on a given date and price to mpf plot. To do this i have the following code:

import pandas as pd
import yfinance as yf
import datetime
from dateutil.relativedelta import relativedelta
import pandas as pd, mplfinance as mpf, matplotlib.pyplot as plt

db = yf.download(tickers='goog', start=datetime.datetime.now()-relativedelta(days=7), end= datetime.datetime.now(), interval="5m")
db = db.dropna()
a = db['Close'][31:32]
test =  mpf.make_addplot(a, type='scatter', markersize=200, marker='^')
mpf.plot(db, type='candle', style= 'charles', addplot=test)

But it is producing the following error:

ValueError: x and y must be the same size

Could you please advise how can i resolve this.

Answer

If your ultimate goal is to add an arrow to the title of the question, you can add it in the way shown in @Daniel Goldfarb’s How to add value of hlines in y axis using mplfinance python. I used this answer to create a code that meets the end goal. As you can see in the answer, the way to do this is to get the axis and then add an annotation for that axis, where 31 is the date/time index and a[0] is the closing price.

import pandas as pd
import yfinance as yf
import datetime
from dateutil.relativedelta import relativedelta
import pandas as pd
import mplfinance as mpf
import matplotlib.pyplot as plt

db = yf.download(tickers='goog', start=datetime.datetime.now()-relativedelta(days=7), end= datetime.datetime.now(), interval="5m")
db = db.dropna()
a = db['Close'][31:32]

#test =  mpf.make_addplot(a, type='scatter', markersize=200, marker='^')
fig, axlist = mpf.plot(db, type='candle', style= 'charles', returnfig=True)#addplot=test

axlist[0].annotate('X', (31, a[0]), fontsize=20, xytext=(34, a[0]+20),
                   color='r', 
                   arrowprops=dict(
                       arrowstyle='->',
                       facecolor='r',
                       edgecolor='r'))
                    
mpf.show()