string.py

"""
Strings are an ordered collection of unicode characters that cannot be
modified at runtime. This module shows how strings are created, iterated,
accessed and concatenated.
"""

# Module-level constants
_DELIMITER = " | "


def main() -> None:
 # Strings are some of the most robust data structures around
 content = "Ultimate Python study guide"

 # We can compute the length of a string just like all other data structures
 assert len(content) > 0

 # We can use range slices to get substrings from a string
 assert content[:8] == "Ultimate"
 assert content[9:15] == "Python"
 assert content[::-1] == "ediug yduts nohtyP etamitlU"

 # Like tuples, we cannot change the data in a string. However, we can
 # create a new string from existing strings
 new_content = f"{content.upper()}{_DELIMITER}{content.lower()}"
 assert _DELIMITER in new_content

 # We can split one string into a list of strings
 split_content = new_content.split(_DELIMITER)
 assert isinstance(split_content, list)
 assert len(split_content) == 2
 assert all(isinstance(item, str) for item in split_content)

 # A two-element list can be decomposed as two variables
 upper_content, lower_content = split_content
 assert upper_content.isupper() and lower_content.islower()

 # Notice that the data in `upper_content` and `lower_content` exists
 # in the `new_content` variable as expected
 assert upper_content in new_content
 assert new_content.startswith(upper_content)
 assert lower_content in new_content
 assert new_content.endswith(lower_content)

 # Notice that `upper_content` and `lower_content` are smaller in length
 # than `new_content` and have the same length as the original `content`
 # they were derived from
 assert len(upper_content) < len(new_content)
 assert len(lower_content) < len(new_content)
 assert len(upper_content) == len(lower_content) == len(content)

 # We can also join `upper_content` and `lower_content` back into one
 # string with the same contents as `new_content`. The `join` method is
 # useful for joining an arbitrary amount of text items together
 joined_content = _DELIMITER.join(split_content)
 assert isinstance(joined_content, str)
 assert new_content == joined_content


if __name__ == "__main__":
 main()