from contextlib import contextmanager

import torch
import torch.nn as nn


@contextmanager
def low_precision_init(target_dtype: torch.dtype = torch.float16):
    dtype = torch.get_default_dtype()
    try:
        torch.set_default_dtype(target_dtype)
        yield
    finally:
        torch.set_default_dtype(dtype)


def get_model_numel(model: nn.Module) -> int:
    return sum(p.numel() for p in model.parameters())


def format_numel_str(numel: int) -> str:
    B = 1024**3
    M = 1024**2
    K = 1024
    if numel >= B:
        return f'{numel / B:.2f} B'
    elif numel >= M:
        return f'{numel / M:.2f} M'
    elif numel >= K:
        return f'{numel / K:.2f} K'
    else:
        return f'{numel}'