len('\\')

len(r'\\')

import re

re.fullmatch(r'a*bb*a((a|b)b*a)*', 'aaaba') is not None

re.fullmatch(r'a*bb*a((a|b)b*a)*', 'aaabab') is not None

re.fullmatch(r'a*bb*a((a|b)b*a)*', 'aaababa') is not None

re.findall(r'<.*>', '<h1>Title</h1><h2>Subtitle</h2>')

re.findall(r'<.*?>', '<h1>Title</h1><h2>Subtitle</h2>')

re.search(r'([_0-9a-zA-Z.]+)?@([_0-9a-zA-Z.]+)', 'My email is d.v.kornev@gmail.com')

mo = re.search(r'([_0-9a-zA-Z.]+)?@([_0-9a-zA-Z.]+)', 'My email is d.v.kornev@gmail.com')

mo.group()

mo.group(0)

mo.group(1)

mo.group(2)

re.fullmatch(r'(.*)cad\1', 'abracadabra') is not None

re.search(r'.*(?= Newton)', 'Isaac Newton')

very_big_data = ['some good string'] * 10000 + ['some bad string'] * 10000

len(very_big_data)

def count_good_strings(data):
    count = 0
    for string in data:
        if re.search(r'good', string) is not None:
            count += 1
    return count

count_good_strings(very_big_data)

%timeit count_good_strings(very_big_data)

def count_good_strings_fast(data):
    regex = re.compile(r'good')
    count = 0
    for string in data:
        if regex.search(string):
            count += 1
    return count

count_good_strings_fast(very_big_data)

%timeit count_good_strings_fast(very_big_data)

import re
import requests

r = requests.get('http://python.org/')
r.text

urls = re.findall(r'<a href="(.+?)"', r.text)
urls

for url in urls:
    print(re.sub(r"^([#/])", r'http://python.org/\1', url))