PySMI library

The MibCompiler object is the top-most interface to PySMI library features. It holds together the otherwise isolated pieces of the compiler infrastructure and manages the workflow of ASN.1 MIB transformation.

This example showcases some of its features:

from pysmi.reader import HttpReader
from pysmi.searcher import StubSearcher
from pysmi.writer import CallbackWriter
from pysmi.parser import SmiStarParser
from pysmi.codegen import JsonCodeGen
from pysmi.compiler import MibCompiler

inputMibs = ['IF-MIB', 'IP-MIB']

httpSources = [('', 80, '/asn1/@mib@')]

# store compiled MIBs by calling this function
def store_mibs(mibName, jsonDoc, cbCtx):
    print('# MIB module %s' % mibName)

mibCompiler = MibCompiler(
    SmiStarParser(), JsonCodeGen(), CallbackWriter(store_mibs)

# pull ASN.1 MIBs over HTTP
mibCompiler.addSources(*[HttpReader(*x) for x in httpSources])

# never recompile MIBs with ASN.1 MACROs

status = mibCompiler.compile(*inputMibs)


MIB sources

PySMI offers a handful of distinct transport mechanisms for fetching MIBs by name from specific locations. In all cases MIB module name to file name match may not be exact – some name fuzzying can be performed to mitigate possible changes to MIB file name.

Conditional compilation

There are cases when MIB transformation may or must not be performed. Such cases include:

  • foundation MIBs containing manually implemented pieces or ASN.1 MACRO’s
  • obsolete MIBs fully reimplemented within modern MIBs
  • already transformed MIBs

MibCompiler expects user to supply a searcher object that would allow or skip MIB transformation for particular name based on whatever reason it is aware of.

In general, searcher logic is specific to target format. At the time being, only pysnmp code generation backend requires such filtering.

Parser configuration

MIBs may be written in one of the two major SMI language versions (v1 and v2). Some MIBs may contain typical errors.

PySMI offers a way to customize the parser to consume either of the major SMI grammars as well as to recover from well-known errors in MIB files.

Code generators

Once ASN.1 MIB is parsed up, AST is passed to a code generator which turns AST into desired representation of the MIB.

Borrow pre-compiled MIBs

Some MIBs in circulation appear broken beyond automatic repair. To handle such cases PySMI introduces the MIB borrowing functionality. When MibCompiler gives up compiling a MIB, it can try to go out and take a copy of already transformed MIB to complete the request successfully.

Write compiled MIBs

Successfully transformed MIB modules’ contents will be passed to writer object given to MibCompiler on instantiation.


The following examples focus on various feature of the PySMI library.

In case of any troubles or confusion, try enabling PySMI debugging and watch the output:

from pysmi import debug