import re
strs= ['AbcS:sdaf', 'AbcSsdaf']
pattern= re.compile(r'([^:]*):')
for s in strs:
m = re.match(pattern, s)
if m:
print(m.group(1))
else:
print(m)
aW1wb3J0IHJlCnN0cnM9IFsnQWJjUzpzZGFmJywgJ0FiY1NzZGFmJ10KcGF0dGVybj0gcmUuY29tcGlsZShyJyhbXjpdKik6JykKZm9yIHMgaW4gc3RyczoKCW0gPSByZS5tYXRjaChwYXR0ZXJuLCBzKQoJaWYgbToKCQlwcmludChtLmdyb3VwKDEpKQoJZWxzZToKCQlwcmludChtKQo=