Creates nested entities

nestedentities.py

#!/usr/bin/env python3
#
"""
<!ENTITY a "aaaaaa">
<!ENTITY b "&a;">
<!ENTITY c "&c;">
 ...
<!ENTITY z "&y;">
"""

import itertools
import sys

__author__ = "Tom Schraitle"


def pairwise(iterable):
    """
    Iterate pairwise over an iterable

    s -> (s0, s1), (s1, s2), (s2, s3), ...
    """
    a, b = itertools.tee(iter(iterable), 2)
    next(b, None)
    return zip(a, b)


def chain(n:int):
    """
    Chain the pairwise tuples

    n=1 -> ("a", "b"), ("b", "c"), ...
    n=2 -> ("aa", "ab"), ("ab", "ac"), ...
    """
    az = [chr(c) for c in range(ord('a'), ord('z')+1)]
    s_az = "".join(az)

    it = pairwise(itertools.product(az, repeat=n))

    for a, b in it:
        yield "".join(a), "".join(b)


def entities(n:int, inittext:str):
    """
    Create lines with <!ENTITY name "value">
    """
    tmpl = '<!ENTITY {a} "{t}">'

    it = chain(n)
    ent, nxt = next(it)
    # Create first two items manually
    yield tmpl.format(a=ent, t=inittext)
    yield tmpl.format(a=nxt, t="&{};".format(ent))

    for ent, nxt in it:
        yield tmpl.format(a=nxt, t="&{};".format(ent))


def get(index:int, default):
    """
    Extract information from sys.argv; if index is not available in
    sys.argv, return default
    """
    try:
        return sys.argv[index]
    except IndexError:
        return default


if __name__ == "__main__":

    n = int(get(1, 1))
    inittext = get(2, "aaaaa")

    for ent in entities(n, inittext):
        print(ent)

# eof