import bs4
html = """<div class="someClass">
<a href="href">
<img alt="some" src="some"/>
</a>
</div>"""
soup = bs4.BeautifulSoup(html, "html.parser")
# this will return src attrib from img tag that is inside 'a' tag
soup.a.img['src']
>>> 'some'
# if you have more then one 'a' tag
for a in soup.find_all('a'):
if a.img:
print(a.img['src'])
>>> 'some'