(Wait for completion... pre-submitted) I use the following approach because my program was replacing a C program, which is naturally faster than Python, so I was looking for ways to optimize this operation. It's very similar to @zeitghaist's answer, but with a couple differences.

encodedData = None
dataLength = 0

with open(self.inputDataFilePath, 'rb') as inputDataFile:
    encodedData = inputDataFile.read()
    dataLength = len(encodedData)

asn1Decoder = asn1tools.compile_files(schemaFilePaths, codec) #BER in my case