$text = 'text';
if(preg_match("/слово/", $text))
{
echo 'есть';
}
else {
echo 'нет';
}

if 'text' in 'some text':
    print 'yes'
else:
    print 'no'

print 'yes' if 'text' in 'some_text' else 'no'

import re
list_of_finded_text = re.findall( r'.*?(слово).*?' , source_text )

import re
text = 'underworld world worldly'
list_of_finded_text = re.findall(r'.*?(world).*?', text)
print(list_of_finded_text)  # Ответ: ['world', 'world', 'world']
res = re.findall(r'\bworld\b', text)
print(res)  # Ответ: ['world']

res = re.search(r'\bслово\b', text) is not None