Scraping days and months from a website using BeautifulSoup

I am to scrap all dates and month of some events from a given website.
There is a special class (for example let's look how days are written):

<span class="date-day">28</span>

My code looks like this:

from bs4 import BeautifulSoup   
soup_2 = BeautifulSoup(r.content, 'html.parser')
temp_1 = soup_2.find_all('span', class_ = 'date-day')
event_day = []
for a in temp_1:
    event_day.append(a['date-day'])

However there is a KeyError which I guess mean that something is wrong with event_day.append(a['date-day']) this part.
How should the proper key look like?
And what is the key for months?

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There is a similar post here but the solution completely doesn't match my problem (or maybe my code is wrong but similar way worked with scraping links and for some alternative texts).