Resolve tokens in strings

tokenstring.py

# :coding: utf-8

"""Replace tokens in strings."""

import re


DOUBLE_CURLY_BRACED_TOKEN = r"{{\s*(\w+)\s*}}"  # E.g.: '{{ token }}'


def resolve(tokenstr, replacements, pattern=DOUBLE_CURLY_BRACED_TOKEN):
    """Apply the replacements dict to the string that contains tokens.

    The replacements can contain tokens themselves: All tokens will be
    expanded if a replacement exists.
    """
    def replace(match):
        """Return replacement for token of match object."""
        token_name = match.groups()[0]
        return replacements[token_name]

    tokenstr, count_replaced = re.subn(pattern, replace, tokenstr)
    # If we replaced at least one thing, we may have added new tokens
    # with that replacement, so give it another try. When the count
    # reaches 0, we have expanded all tokens that we know of.
    while count_replaced:
        tokenstr, count_replaced = re.subn(pattern, replace, tokenstr)
    return tokenstr


def test_resolve():
    teststring = "This is a {{ nested }} {{ test }}, {{mod}}."
    replacements = {"test": "working example",
                    "nested": "{{ mod }}",
                    "mod": "really"}
    expectation = "This is a really working example, really."

    result = resolve(teststring, replacements)
    assert result == expectation