function - defines pytensor.function

Guide

This module provides function(), commonly accessed as pytensor.function, the interface for compiling graphs into callable objects.

You’ve already seen example usage in the basic tutorial… something like this:

>>> import pytensor
>>> x = pytensor.tensor.dscalar()
>>> f = pytensor.function([x], 2*x)
>>> f(4)
array(8.0)

The idea here is that we’ve compiled the symbolic graph (2*x) into a function that can be called on a number and will do some computations.

The behaviour of function can be controlled in several ways, such as In, Out, mode, updates, and givens. These are covered in the tutorial examples and tutorial on modes.

Reference

class pytensor.compile.function.In

A class for attaching information to function inputs.

variable

A variable in an expression graph to use as a compiled-function parameter

name

A string to identify an argument for this parameter in keyword arguments.

value

The default value to use at call-time (can also be a Container where the function will find a value at call-time.)

update

An expression which indicates updates to the Value after each function call.

mutable

True means the compiled-function is allowed to modify this argument. False means it is not allowed.

borrow

True indicates that a reference to internal storage may be returned, and that the caller is aware that subsequent function evaluations might overwrite this memory.

strict

If False, a function argument may be copied or cast to match the type required by the parameter variable. If True, a function argument must exactly match the type required by variable.

allow_downcast

True indicates that the value you pass for this input can be silently downcasted to fit the right type, which may lose precision. (Only applies when strict is False.)

autoname

True means that the name is set to variable.name.

implicit

True means that the input is implicit in the sense that the user is not allowed to provide a value for it. Requires ‘value’ to be set. False means that the user can provide a value for this input.

__init__(self, variable, name=None, value=None, update=None, mutable=None, strict=False, allow_downcast=None, autoname=True, implicit=None, borrow=None, shared=False)

Initialize attributes from arguments.

class pytensor.compile.function.Out

A class for attaching information to function outputs

variable

A variable in an expression graph to use as a compiled-function output

borrow

True indicates that a reference to internal storage may be returned, and that the caller is aware that subsequent function evaluations might overwrite this memory.

__init__(variable, borrow=False)

Initialize attributes from arguments.

pytensor.compile.function.function(inputs, outputs, mode=None, updates=None, givens=None, no_default_updates=False, accept_inplace=False, name=None, rebuild_strict=True, allow_input_downcast=None, profile=None, on_unused_input='raise')

Return a callable object that will calculate outputs from inputs.

Parameters:

• params (list of either Variable or In instances, but not shared variables.) – the returned Function instance will have parameters for these variables.

• outputs (list of Variables or Out instances) – expressions to compute.

• mode (None, string or Mode instance.) – compilation mode

• updates (iterable over pairs (shared_variable, new_expression). List, tuple or dict.) – expressions for new SharedVariable values

• givens (iterable over pairs (Var1, Var2) of Variables. List, tuple or dict. The Var1 and Var2 in each pair must have the same Type.) – specific substitutions to make in the computation graph (Var2 replaces Var1).

• no_default_updates (either bool or list of Variables) – if True, do not perform any automatic update on Variables. If False (default), perform them all. Else, perform automatic updates on all Variables that are neither in updates nor in no_default_updates.

• name – an optional name for this function. The profile mode will print the time spent in this function.

• rebuild_strict – True (Default) is the safer and better tested setting, in which case givens must substitute new variables with the same Type as the variables they replace. False is a you-better-know-what-you-are-doing setting, that permits givens to replace variables with new variables of any Type. The consequence of changing a Type is that all results depending on that variable may have a different Type too (the graph is rebuilt from inputs to outputs). If one of the new types does not make sense for one of the Ops in the graph, an Exception will be raised.

• allow_input_downcast (Boolean or None) – True means that the values passed as inputs when calling the function can be silently downcasted to fit the dtype of the corresponding Variable, which may lose precision. False means that it will only be cast to a more general, or precise, type. None (default) is almost like False, but allows downcasting of Python float scalars to floatX.

• profile (None, True, or ProfileStats instance) – accumulate profiling information into a given ProfileStats instance. If argument is True then a new ProfileStats instance will be used. This profiling object will be available via self.profile.

• on_unused_input – What to do if a variable in the ‘inputs’ list is not used in the graph. Possible values are ‘raise’, ‘warn’, and ‘ignore’.

Return type:

Function instance

Returns:

a callable object that will compute the outputs (given the inputs) and update the implicit function arguments according to the updates.

Inputs can be given as variables or In instances. In instances also have a variable, but they attach some extra information about how call-time arguments corresponding to that variable should be used. Similarly, Out instances can attach information about how output variables should be returned.

The default is typically ‘FAST_RUN’ but this can be changed in pytensor.config. The mode argument controls the sort of rewrites that will be applied to the graph, and the way the rewritten graph will be evaluated.

After each function evaluation, the updates mechanism can replace the value of any (implicit) SharedVariable inputs with new values computed from the expressions in the updates list. An exception will be raised if you give two update expressions for the same SharedVariable input (that doesn’t make sense).

If a SharedVariable is not given an update expression, but has a Variable.default_update member containing an expression, this expression will be used as the update expression for this variable. Passing no_default_updates=True to function disables this behavior entirely, passing no_default_updates=[sharedvar1, sharedvar2] disables it for the mentioned variables.

Regarding givens: Be careful to make sure that these substitutions are independent, because behaviour when Var1 of one pair appears in the graph leading to Var2 in another expression is undefined (e.g. with {a: x, b: a + 1}). Replacements specified with givens are different from replacements that occur during normal rewriting, in that Var2 is not expected to be equivalent to Var1.

pytensor.compile.function.function_dump(filename, inputs, outputs=None, mode=None, updates=None, givens=None, no_default_updates=False, accept_inplace=False, name=None, rebuild_strict=True, allow_input_downcast=None, profile=None, on_unused_input=None, extra_tag_to_remove=None, trust_input=False)

This is helpful to make a reproducible case for problems during PyTensor compilation.

Ex:

replace pytensor.function(...) by pytensor.function_dump('filename.pkl', ...).

If you see this, you were probably asked to use this function to help debug a particular case during the compilation of an PyTensor function. function_dump allows you to easily reproduce your compilation without generating any code. It pickles all the objects and parameters needed to reproduce a call to pytensor.function(). This includes shared variables and their values. If you do not want that, you can choose to replace shared variables values with zeros by calling set_value(…) on them before calling function_dump.

To load such a dump and do the compilation:

>>> import pickle
>>> import pytensor
>>> d = pickle.load(open("func_dump.bin", "rb"))  
>>> f = pytensor.function(**d)  

Note: The parameter extra_tag_to_remove is passed to the StripPickler used. To pickle graph made by Blocks, it must be: ['annotations', 'replacement_of', 'aggregation_scheme', 'roles']

class pytensor.compile.function.types.Function(vm, input_storage, output_storage, indices, outputs, defaults, unpack_single, return_none, output_keys, maker, trust_input=False, name=None)

A class that wraps the execution of a VM making it easier for use as a “function”.

Function is the callable object that does computation. It has the storage of inputs and outputs, performs the packing and unpacking of inputs and return values. It implements the square-bracket indexing so that you can look up the value of a symbolic node.

Functions are copyable via Function.copy and the copy.copy interface. When a function is copied, this instance is duplicated. Contrast with self.maker (instance of FunctionMaker) that is shared between copies. The meaning of copying a function is that the containers and their current values will all be duplicated. This requires that mutable inputs be copied, whereas immutable inputs may be shared between copies.

A Function instance is hashable, on the basis of its memory address (its id). A Function instance is only equal to itself. A Function instance may be serialized using the pickle or cPickle modules. This will save all default inputs, the graph, and WRITEME to the pickle file.

A Function instance has a Function.trust_input field that defaults to False. When True, the Function will skip all checks on the inputs.

finder

Dictionary mapping several kinds of things to containers.

We set an entry in finder for: - the index of the input - the variable instance the input is based on - the name of the input

All entries map to the container or to DUPLICATE if an ambiguity is detected.

inv_finder

Reverse lookup of finder. It maps containers to SymbolicInputs.

__call__(*args, output_subset=None, **kwargs)

Evaluates value of a function on given arguments.

Parameters:

• args (list) – List of inputs to the function. All inputs are required, even when some of them are not necessary to calculate requested subset of outputs.

• kwargs (dict) –

  The function inputs can be passed as keyword argument. For this, use the name of the input or the input instance as the key.

  Keyword argument output_subset is a list of either indices of the function’s outputs or the keys belonging to the output_keys dict and represent outputs that are requested to be calculated. Regardless of the presence of output_subset, the updates are always calculated and processed. To disable the updates, you should use the copy method with delete_updates=True.

Returns:

List of outputs on indices/keys from output_subset or all of them, if output_subset is not passed.

Return type:

list

copy(share_memory=False, swap=None, delete_updates=False, name=None, profile=None)

Copy this function. Copied function will have separated maker and fgraph with original function. User can choose whether to separate storage by changing the share_memory arguments.

Parameters:

• share_memory (boolean) – When True, two function share intermediate storages(storages except input and output storages). Otherwise two functions will only share partial storages and same maker. If two functions share memory and allow_gc=False, this will increase executing speed and save memory.

• swap (dict) – Dictionary that map old SharedVariables to new SharedVariables. Default is None. NOTE: The shared variable swap in only done in the new returned function, not in the user graph.

• delete_updates (boolean) – If True, Copied function will not have updates.

• name (string) – If provided, will be the name of the new Function. Otherwise, it will be old + “ copy”

• profile (bool | str | ProfileStats | None) – as pytensor.function profile parameter

Returns:

Copied pytensor.Function

Return type:

pytensor.Function

free()

When allow_gc = False, clear the Variables in storage_map