Quickstart Guide

vmt-util provides utility functions and classes for vmt-connect, and does not itself provide any direct API methods or calls. The most useful functions will likely be evaluate, and unit_cast which has two pre-built wrappers: mem_cast and cpu_cast.

Unit Conversions

The base conversion utility unit_cast is a general purpose unit converter for scales that have a static conversion factor, such as metric measurements. Two convenience wrapper functions are provided to make repetetive conversions easier.

Suppose we have pulled VM statistics and wish to convert the VMem from the reported value in KB, to something more useful such as GB for reporting. Assuming we have stored our value in a variable called vm_memory, we might do like so:

mem_cast(vm_memory)

And if we wanted it in an alternate unit, such as TB or MB, we could specify the destination unit to the cast function.

# memory in TB
mem_cast(vm_memory, 'TB')

# memory in GB
mem_cast(vm_memory, 'MB')

Likewise, there is a convenience wrapper for CPU speeds reported in Mhz, which defaults to Ghz.

# speed in Ghz
cpu_cast(cpu_speed)

# speed in Thz
cpu_cast(cpu_speed, 'THZ')

Expression Parser

The evaluate function provides an extensible expression parser which may be adapted as needed to create domain specific languages for advanced configurations. The base expression syntax is CPython.

# basic expression evaluation
exp = '1 + 10 / 5'
evaluate(exp)

# returns 3

# this also returns 3
exp = 'int(5 / 2 + 1.4)'
evaluate(exp)

Control flow capabilities are intentionally not present within the base expression syntax, though as shown above, functions are, including most safe default Pthon functions. Additionally, the parser may be extended with custom functions using a mapper dictionary.

import random

# our own unique function
def number():
    return random.random() * 10

# map our function to the name we want the parser to recognize
map = {"get_num": number}

exp = 'get_num() < 5'
evaluate(exp, map)

# returns True or False depending on results of get_num() at runtime

Multiple logic conditions can be combined, the same as in Python.

def number():
    return random.random() * 10

def status_check():
    # produce some conditional response
    return True

map = {"get_num": number, "status": status_check}
exp = '(get_num() < 5 and get_num() > 1) or !status()'
evaluate(exp, map)