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(beta) Bundling inputs to PyTorch Models

Author: Jacob Szwejbka

Introduction

This tutorial introduces the steps to use PyTorch’s utility to bundle example or trivial inputs directly into your TorchScript Module.

The interface of the model remains unchanged (other than adding a few methods), so it can still be safely deployed to production. The advantage of this standardized interface is that tools that run models can use it instead of having some sort of external file (or worse, document) that tells you how to run the model properly.

Common case, bundling an input to a model that only uses ‘forward’ for inference

  1. Prepare model: Convert your model to TorchScript through either tracing or scripting

import torch
import torch.jit
import torch.utils
import torch.utils.bundled_inputs

class Net(nn.Module):
    def __init__(self):
        super(Net, self).__init__()
        self.lin = nn.Linear(10, 1)

    def forward(self, x):
        return self.lin(x)

model = Net()
scripted_module = torch.jit.script(model)
  1. Create example input and attach to model

# For each method create a list of inputs and each input is a tuple of arguments
sample_input = [(torch.zeros(1,10),)]

# Create model with bundled inputs, if type(input) is list then the input is bundled to 'forward'
bundled_model = bundle_inputs(scripted_module, sample_input)
  1. Run model with input as arguments

sample_inputs = bundled_model.get_all_bundled_inputs()

print(bundled_model(*sample_inputs[0]))

Uncommon case, bundling and retrieving inputs for functions beyond ‘forward’

  1. Prepare model: Convert your model to TorchScript through either tracing or scripting

import torch
import torch.jit
import torch.utils
import torch.utils.bundled_inputs
from typing import Dict

class Net(nn.Module):
    def __init__(self):
        super(Net, self).__init__()
        self.lin = nn.Linear(10, 1)

    def forward(self, x):
        return self.lin(x)

    @torch.jit.export
    def foo(self, x: Dict[String, int]):
        return x['a'] + x['b']


model = Net()
scripted_module = torch.jit.script(model)
  1. Create example input and attach to model

# For each method create a list of inputs and each input is a tuple of arguments
example_dict = {'a' : 1, 'b' : 2}
sample_input = {
    scripted_module.forward : [(torch.zeros(1,10),)],
    scripted_module.foo : [(example_dict,)]
}

# Create model with bundled inputs, if type(sample_input) is Dict then each callable key is mapped to its corresponding bundled input
bundled_model = bundle_inputs(scripted_module, sample_input)
  1. Retrieve inputs and run model on them

all_info = bundled_model.get_bundled_inputs_functions_and_info()

# The return type for get_bundled_inputs_functions_and_info is complex, but essentially we are retrieving the name
# of a function we can use to get the bundled input for our models method
for func_name in all_info.keys():
    input_func_name = all_info[func_name]['get_inputs_function_name'][0]
    func_to_run = getattr(bundled_model, input_func_name)
    # retrieve input
    sample_input = func_to_run()
    model_function = getattr(bundled_model, func_name)
    for i in range(len(sample_input)):
        print(model_function(*sample_input[i]))

Inflatable args

Attaching inputs to models can result in nontrivial size increases. Inflatable args are a way to compress and decompress inputs to minimize this impact.

Note

Any automatic compression, or parsing of inflatable args only happens to top level arguments in the input tuple.

  • ie if your model takes in a List type of inputs you would need to create an inflatable arg that returned a list not create a list of inflatable args.

  1. Existing Inflatable args

The following input types are compressed automatically without requiring an explicit inflatable arg:
  • Small contiguous tensors are cloned to have small storage.

  • Inputs from torch.zeros, torch.ones, or torch.full are moved to their compact representations.

# bundle_randn will generate a random tensor when the model is asked for bundled inputs
sample_inputs = [(torch.utils.bundled_inputs.bundle_randn((1,10)),)]
bundled_model = bundle_inputs(scripted_module, sample_inputs)
print(bundled_model.get_all_bundled_inputs())
  1. Creating your own

Inflatable args are composed of 2 parts, the deflated (compressed) argument, and an expression or function definition to inflate them.

def create_example(*size, dtype=None):
    """Generate a tuple of 2 random tensors both of the specified size"""

    deflated_input = (torch.zeros(1, dtype=dtype).expand(*size), torch.zeros(1, dtype=dtype).expand(*size))

    # {0} is how you access your deflated value in the inflation expression
    return torch.utils.bundled_inputs.InflatableArg(
        value=stub,
        fmt="(torch.randn_like({0}[0]), torch.randn_like({0}[1]))",
    )
  1. Using a function instead

    If you need to create a more complicated input providing a function is an easy alternative

sample = dict(
    a=torch.zeros([10, 20]),
    b=torch.zeros([1, 1]),
    c=torch.zeros([10, 20]),
)

def condensed(t):
    ret = torch.empty_like(t).flatten()[0].clone().expand(t.shape)
    assert ret.storage().size() == 1
    return ret

# An example of how to create an inflatable arg for a complex model input like Optional[Dict[str, Tensor]]
# here we take in a normal input, deflate it, and define an inflater function that converts the mapped tensors to random values
def bundle_optional_dict_of_randn(template: Optional[Dict[str, Tensor]]):
    return torch.utils.bundled_inputs.InflatableArg(
        value=(
            None
            if template is None
            else {k: condensed(v) for (k, v) in template.items()}
        ),
        fmt="{}",
        fmt_fn="""
        def {}(self, value: Optional[Dict[str, Tensor]]):
            if value is not None:
                output = {{}}
                for k, v in value.items():
                    output[k] = torch.randn_like(v)
                return output
            else:
                return None
        """,
    )

sample_inputs = (
    bundle_optional_dict_of_randn(sample),
)

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