macos default fd ulimit is 256. why do i see 252?

fd.py

import tempfile

files = []

while True:
    try:
        file = tempfile.TemporaryFile()
        print("Created file:", file, file.name)
        files.append(file)
    except OSError:
        print("Total: {}".format(len(files)))
        break

for x in files:
    x.close()

oh but when i try it in python 3, it starts at 3:

10292 ◯  python3 fd.py
Created file: <_io.BufferedRandom name=3> 3
Created file: <_io.BufferedRandom name=4> 4
Created file: <_io.BufferedRandom name=5> 5
...
Created file: <_io.BufferedRandom name=254> 254
Created file: <_io.BufferedRandom name=255> 255
Total: 253

It gets one additional file in the count somehow

(this is 3.6) python 3 still gives me

Max for process: 8
Traceback (most recent call last):
  File "fd.py", line 16, in <module>
AttributeError: module 'resource' has no attribute 'RLIMIT_OFILE'

lolololol real dingus hours right here, these look and act like enums. here's how i should be doing it:

print("Max for process:", resource.getrlimit(resource.RLIMIT_NOFILE))
print("Max for process:", resource.getrlimit(resource.RLIMIT_OFILE))

Max for process: (256, 9223372036854775807)
Traceback (most recent call last):
  File "fd.py", line 16, in <module>
AttributeError: module 'resource' has no attribute 'RLIMIT_OFILE'

I wonder what 9223372036854775807 is 2^64-1. that tuple output is (soft, hard) limits.