Recursion remover for CFG

example_input.txt

X XaZ|YWc|W
Y Yd|WbZ|ZWc|X
W WXa|ZZd|YYe|c
Z XX|Zc

recursion_remover.py

import sys

all_prods = []

line = None
while line != '':
    line = input(
            'Production as A bc|d (or ""): '
            if sys.stdin.isatty()
            else ''
    )
    if not line:
        break

    letter = line[0]
    line = line[2:]
    letter_prods = [ [*prod] for prod in line.split('|') ]

    all_prods.append([letter, letter_prods])

def print_prods():
    for i, [letter, prods] in enumerate(all_prods):
        print(f'{letter:<2} -> ', end='')
        for ip, prod in enumerate(prods):
            for prod_l in prod:
                print(f'{prod_l:<2}', end=' ')
            if not prod:
                print('ε', end='')

            print()
            if ip < len(prods) - 1:
                print('    | ', end='')

        print()

    print('-'*15)
    print()

print('INIZIO')
print_prods()

for i, [curr_l, curr_p] in enumerate(all_prods):
    if curr_l.endswith("'"): continue

    # Prev letters
    for prev_l, prev_p in all_prods[:i]:
        if prev_l.endswith("'"): continue

        all_prods[i][1] = curr_p = [
                p
                for p in curr_p
                if p[0] != prev_l
            ] + [
                prev_pp + p[1:]
                for prev_pp in prev_p
                for p in curr_p
                if p[0] == prev_l
            ]
        print(f'POST SUBS {prev_l} IN {curr_l}')
        print_prods()

    # Current recursion
    all_prods[i][1] = [ # curr_p assigned
                p + [curr_l + "'"]
                for p in curr_p
                if p[0] != curr_l
            ]

    # New variable X'
    all_prods.append([curr_l + "'", [
            p[1:] + [curr_l + "'"]
            for p in curr_p
            if p[0] == curr_l
        ] + [[
            # Epsilon
            ]]
    ])

    print(f'POST IMMEDIATE {curr_l}')
    print_prods()

# Sort by letter
all_prods.sort(key=lambda prod: prod[0])

print('FINALE')
print_prods()