import re

haystack = "Hello world"
needle = 'ello'

mo = re.search(needle, haystack)
print(mo)

# Does not work on python 3.6:
# assert isinstance(mo, re.Match)
assert mo.start() == 1
assert mo.end() == 5

assert re.escape('python.exe') == 'python\\.exe'

p = re.compile('ab')
s = p.sub('x', 'abcabca')
print(s)
assert s == 'xcxca'

idpattern = r'([_a-z][_a-z0-9]*)'

mo = re.search(idpattern, '7382 _boe0+2')
print(mo)
# TODO:
# assert mo.group(0) == '_boe0'