(CkPython) How to Tell if a File is .p7m or .p7s

This example explains how to detect if a file is a .p7m or .p7s. It provides as solution to the following problem:

Sometimes people submit P7S/P7M with wrong extensions. Can I check if file is P7S or P7M with Chilkat?

Also see What is a P7M or P7S File?

Chilkat Python Downloads install with pip pip3 install chilkat or download... Python Module for Windows, MacOS, Linux, Alpine Linux, Solaris

import sys
import chilkat

# A .p7m or .p7s file is binary and contains PKCS7.
# PKCS7 is ASN.1, and always begins with a SEQUENCE tag (a byte equal to 0x30)
# followed by an encoded length.
# If the file is larger than 128 bytes (and it SHOULD be), the encoded length will begin with either 0x80, 0x81, 0x82, or 0x83.
# It can also begin with 0x84, but only for very large files (where the length is too large for 3 bytes).
# See How ASN.1 Encodes Lengths

# Therefore, if we have a file that might be .p7m or .p7s, we can check by
# examining the 1st 2 bytes of the file.

bd = chilkat.CkBinData()

success = bd.LoadFile("qa_data/p7m/a.p7m")
if (success == False):
    print("Failed to load the file.")
    sys.exit()

sb = chilkat.CkStringBuilder()
sb.Append(bd.getEncodedChunk(0,2,"hex"))

caseSensitive = True
if (sb.ContentsEqual("3080",caseSensitive) or sb.ContentsEqual("3081",caseSensitive) or sb.ContentsEqual("3082",caseSensitive) or sb.ContentsEqual("3083",caseSensitive)):
    print("This is a .p7m or .p7s file.")
else:
    print("This is not a .p7m or .p7s file.")