def match(text, pattern):
        if not pattern: return not text
        first_match = bool(text) and pattern[0] in {text[0], '.'}
        return first_match and match(text[1:], pattern[1:])

I'm new to python and I don't understand the syntax. What is the purpose of elements in braces and what does "bool(text) and pattern[0] in {text[0], '.'}"

CodePudding user response：

In python, braces are used to create either a dictionary, or a set.

    my_set = {1, 2, 3}
    my_dict = {'a': 1, 'b': 2, 'c': 3}

bool(text) and pattern[0] in {text[0], '.'} is checking whether the text is true (i.e. not empty or false), and the first element in pattern is either equal to text[0] or is a '.'

CodePudding user response：

If we were to destruct your function into distinct pieces, it will be easier to understand

def match(text: str, pattern: str) -> bool:
    # if pattern is an empty string or None
    if not pattern:
        # True if text is empty string or None, otherwise - false
        result: bool = not text
        return result

    # If text is empty or None return False
    if not text:
        return False

    # Equivalent to set(first letter of text, dot)
    # We use set/{} instead of list/[] or tuple/() to remove duplicates, 
    # however i don't see why should we care about duplicated dots here
    subset: set = {text[0], '.'}

    # If first letter of pattern is not in subset, return False
    if pattern[0] not in subset:
       return False

    # Go one level deeper in recursion and return it's answer
    result: bool = match(text[1:], pattern[1:])
    return result

About curly braces. In python they mean two things:

• dict / dictionary: {"foo": "bar", "count": 10}
• set / unique list: {1, 2, 3, 3} will create set {1, 2, 3}

Follow the links to learn more from python's docs