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"""

Regular expressions is a way to search text efficiently. Implementing them

is difficult but thankfully Python provides a package for us to use them

easily. This module shows a few examples of how to use the `re` package to

search predefined text snippets stored in module-level constants.

"""

import re

# Module-level constants

_TEXT_HELLO = "World Hello Hello"

_TEXT_NAMES = "John, Jane"

_TEXT_ABC123 = "abc123"

_TEXT_BYE = "Bye for now"

def main():

# Running `search` with "Hello" has a match for first Hello

assert re.search(r"Hello", _TEXT_HELLO).start() == 6

# Running `search` with "Hello$" has a match for last Hello

assert re.search(r"Hello$", _TEXT_HELLO).start() == 12

# Running `search` with "(Hello) (Hello)" has matches for Hello

assert re.search(r"(Hello) (Hello)", _TEXT_HELLO).groups() == ("Hello", "Hello")

# Running `findall` with "Hi \w+" has a list of strings

assert re.findall(r"\w+", _TEXT_NAMES) == ["John", "Jane"]

# Running `match` with "[123]+" has nothing

assert re.match(r"[123]+", _TEXT_ABC123) is None

# Running `match` with "[abc]+" has a match for abc

assert re.match(r"[abc]+", _TEXT_ABC123).group(0) == "abc"

# Running `fullmatch` with "[\w]+" has nothing

assert re.fullmatch(r"[\w]+", _TEXT_BYE) is None

# Running `fullmatch` with "[\w ]+" has a full match

assert re.fullmatch(r"[\w ]+", _TEXT_BYE).group(0) == _TEXT_BYE

# To learn more about regular expressions:

# https://en.wikipedia.org/wiki/Regular_expression

# https://github.com/ziishaned/learn-regex

# To play around with regular expressions in the browser:

# https://regex101.com

if __name__ == "__main__":

main()