Python string formatting when string contains “%s” without escaping

Question

When formatting a string, my string may contain a modulo \"%\" that I do not wish to have converted. I can escape the string and change each \"%\"

Answer 1

You can use regular expressions to replace % by %% where % is not followed by (

def format_with_dict(str, dictionary):
    str = re.sub(r"%([^\(])", r"%%\1", str)
    str = re.sub(r"%$", r"%%", str)  # There was a % at the end?
    return str % dictionary

This way:

print format_with_dict('Day old bread, 50% sale %(when)s', {'when': 'today'})

Will output:

Day old bread, 50% sale today

This method is useful to avoid "not enough arguments for format string" errors.