pyeda.util — Utilities

The pyeda.util module contains top-level utilities, such as fundamental functions and decorators.

Interface Functions:

• bit_on() — Return the value of a number’s bit position
• clog2() — Return the ceiling log base two of an integer
• parity() — Return the parity of an integer

Decorators:

• cached_property()

Interface Functions

pyeda.util.bit_on(num: int, bit: int) → int

Return the value of a number’s bit position.

For example, since \(42 = 2^1 + 2^3 + 2^5\), this function will return 1 in bit positions 1, 3, 5:

>>> [bit_on(42, i) for i in range(clog2(42))]
[0, 1, 0, 1, 0, 1]

pyeda.util.clog2(num: int) → int

Return the ceiling log base two of an integer \(\ge 1\).

This function tells you the minimum dimension of a Boolean space with at least N points.

For example, here are the values of clog2(N) for \(1 \le N < 18\):

>>> [clog2(n) for n in range(1, 18)]
[0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 5]

This function is undefined for non-positive integers:

>>> clog2(0)
Traceback (most recent call last):
    ...
ValueError: expected num >= 1

pyeda.util.parity(num: int) → int

Return the parity of a non-negative integer.

For example, here are the parities of the first ten integers:

>>> [parity(n) for n in range(10)]
[0, 1, 1, 0, 1, 0, 0, 1, 1, 0]

This function is undefined for negative integers:

>>> parity(-1)
Traceback (most recent call last):
    ...
ValueError: expected num >= 0

Decorators

pyeda.util.cached_property(func)

Return a cached property calculated by the input function.

Unlike the property decorator builtin, this decorator will cache the return value in order to avoid repeated calculations. This is particularly useful when the property involves some non-trivial computation.

For example, consider a class that models a right triangle. The hypotenuse c will only be calculated once.

import math

class RightTriangle:
    def __init__(self, a, b):
        self.a = a
        self.b = b

    @cached_property
    def c(self):
        return math.sqrt(self.a**2 + self.b**2)