markdown.py

text = """Text attributes _italic_, **bold**, `monospace`. Some implementations may use *single-asterisks* for italic text."""

expected = """<p>Text attributes <em>italic</em>, <strong>bold</strong>, <code>monospace</code>. Some implementations may use <i>single-asterisks</i> for italic text.</p>"""

def lookup(text, start, size):
    return text[start:start+size]

token_italic = "_"
token_italic_alt = "*"
token_strong = "**"
token_monospace = "`"

def tokenize(text):
    index = 0
    result = []
    while index < len(text):
        if lookup(text, index, 2) == token_strong:
            result.append(token_strong)
            index += 2
        elif lookup(text, index, 1) == token_italic:
            result.append(token_italic)
            index += 1
        elif lookup(text, index, 1) == token_italic_alt:
            result.append(token_italic_alt)
            index += 1
        elif lookup(text, index, 1) == token_monospace:
            result.append(token_monospace)
            index += 1
        else:
            result.append(lookup(text, index, 1))
            index += 1
            
    return result

tokens = tokenize(text)

flags = {
    "italic": False,
    "italic_alt": False,
    "strong": False,
    "monospace": False,
}

paragraph_start = "<p>"
paragraph_end = "</p>"
italic_start = "<em>"
italic_end = "</em>"
italic_alt_start = "<i>"
italic_alt_end = "</i>"
strong_start = "<strong>"
strong_end = "</strong>"
monospace_start = "<code>"
monospace_end = "</code>"

result = ""
for token in tokens:
    if token == token_italic:
        flags["italic"] = not flags["italic"]
        result += italic_start if flags["italic"] else italic_end
    elif token == token_italic_alt:
        flags["italic_alt"] = not flags["italic_alt"]
        result += italic_alt_start if flags["italic_alt"] else italic_alt_end
    elif token == token_strong:
        flags["strong"] = not flags["strong"]
        result += strong_start if flags["strong"] else strong_end
    elif token == token_monospace:
        flags["monospace"] = not flags["monospace"]
        result += monospace_start if flags["monospace"] else monospace_end
    else:
        result += token
        
actual = paragraph_start + result + paragraph_end
        
print(tokens)
print(actual)
print(expected)
assert actual == expected