Заменить каждую букву на цифру в большом текстовом файле

s = input('Введите предложение на английском: ')
print( *list( map( lambda x: 0 if x==' ' else ord(x.lower())-ord('a')+1 if x.isalpha() else x, s ) ) )

with open('in_text.txt', 'r') as f:
    text = f.read()
rez = ''
for i in text:
    if ord(i) in range(97,123):
        rez += str(ord(i))
    elif ord(i) in range(65,91):
        rez += f'0{ord(i)}'
    else:
        rez += i
with open('out_text.txt', 'w') as f:
    f.write(rez)

with open('in_text.txt', 'r') as f:
    text = f.read()
rez = ''
for i in text:
    if ord(i) in range(97,123):
        rez += str(ord(i) - 96)
    elif ord(i) in range(65,91):
        rez += f'0{ord(i) - 64}'
    else:
        rez += i
with open('out_text.txt', 'w') as f:
    f.write(rez)

def let_to_num(symb):
    if 'a' <= symb.lower() <= 'z':
         return ('0' if symb.isupper() else '') + str(ord(symb.lower()) - ord('a') + 1)
    return symb
open('out.txt', 'w').write(''.join(map(let_to_num, open('in.txt').read())))

from string import ascii_lowercase
def let_to_num(symb):
    try:        return ('','0')[symb.isupper()] + str(ascii_lowercase.index(symb.lower()) + 1)
    except:     return symb
open('out.txt','w').write(''.join(map(let_to_num, open('in.txt').read())))

from string import ascii_lowercase, ascii_uppercase
from contextlib import suppress
def let_to_num(symb):
    with suppress(ValueError): return str(ascii_lowercase.index(symb) + 1)
    with suppress(ValueError): return '0' + str(ascii_uppercase.index(symb) + 1)
    return symb
open('out.txt','w').write(''.join(map(let_to_num, open('in.txt').read())))

from string import ascii_lowercase
def let_to_num(symb):
    try:        return ('','0')[symb.isupper()] + str(ascii_lowercase.index(symb.lower()) + 1)
    except:     return symb
with open('in.txt') as in_f:
    with open('out.txt','a') as out_f:
        while True:
            piece = in_f.read(512*1024)
            if not piece:
                break
            out_f.write(''.join(map(let_to_num, piece)))