find_placeholders.py

import re

# According to printf format string specification from Wikipedia, the format is:
# %[parameter][flags][width][.precision][length]type
# see http://en.wikipedia.org/wiki/Printf_format_string#Format_placeholders
PLACEHOLDERS_REGEX = """
    (                                       # Capture everything in group 1
    %                                       # Look for a literal '%'
    (?:                                     # Match an actual placeholder (and not '%%')
    (?:\d+\$)?                              # Look for an optional paramter - number and then '$'
    [-+ 0#]{0,5}                            # 0 to 5 optional flags
    (?:\d+|\*)?                             # Optional width
    (?:\.(?:\d+|\*))?                       # Optional precision
    (?:hh|h|l|ll|L|z|j|t|q|I|I32|I64|w)?    # Optional length
    [diufFeEgGxXoscqaAn]                    # Type
    |                                       # OR
    %))                                     # literal "%%"
    """


def find_placeholders_in_format_string(format_string):
    """
    Find inside a C-style format string, all the the placeholders for parameters
    i.e. for "Worker name is %s and id is %d" will return the indexes and the placeholders:
    [(15, "%s"), (28, "%d")]
    :param format_string: The string to find placeholders in
    :return: List of placeholders location and value
    """

    matches = re.finditer(PLACEHOLDERS_REGEX, format_string, flags=re.X)
    results = []
    for i in matches:
        # Remove all the "%%" found. These are literal "%", not placeholders
        if i.group(0) != "%%":
            results.append((i.start(0), i.group(0)))
    return results