Tools to convert between dictionaries and strings with proper escaping

dictionary_to_string.py

_ENCODED_ESCAPE_TRANSLATION = str.maketrans({
    '\\': r'\\',
    ',': r'\,',
    '=': r'\=',
})

def dictionary_to_string(d):

    components = [
        '{}={}'.format(
            str(key).translate(_ENCODED_ESCAPE_TRANSLATION),
            str(value).translate(_ENCODED_ESCAPE_TRANSLATION))

        for key, value
        in d.items()
    ]

    encoded = ','.join(components)
    return encoded

def _split_by_unescaped_character(s, separator):

    last = 0
    for i, c in enumerate(s):
        if c != separator:
            continue
        elif i > 0 and s[i - 1] == '\\':
            continue

        value = s[last:i]
        yield value

        last = i + 1

    value = s[last:]
    yield value

def _unescape(s):

    # Process the string in reverse, because we'll need to 'lookahead' in order
    # to skip the preceding slashes

    chars = []
    len_ = len(s)
    i = 0
    r = list(reversed(s))
    while i < len_:
        c = r[i]
        chars.append(c)

        i += 1

        # If it was escaped, remove the slash and step another position
        if i < len_ and r[i] == '\\':
            i += 1


    return ''.join(reversed(chars))

def string_to_dictionary(s):

    components = _split_by_unescaped_character(s, ',')
    components = list(components)

    d = {}
    for component in components:

        couplet = _split_by_unescaped_character(component, '=')
        couplet = list(couplet)

        assert \
            len(couplet) == 2, \
            "Name-value couplet does not have two parts: {}".format(couplet)

        escaped_key, escaped_value = couplet

        key = _unescape(escaped_key)
        value = _unescape(escaped_value)

        d[key] = value

    return d