Source code for pennylane.measurements.shots
# Copyright 2018-2023 Xanadu Quantum Technologies Inc.
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# http://www.apache.org/licenses/LICENSE-2.0
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""This module contains the Shots class to hold shot-related information."""
# pylint:disable=inconsistent-return-statements
from typing import NamedTuple
from typing import Sequence, Tuple
[docs]class ShotCopies(NamedTuple):
"""A namedtuple that represents a shot quantity being repeated some number of times.
For example, ``ShotCopies(10 shots x 2)`` indicates two executions with 10 shots each for 20 shots total.
"""
shots: int
copies: int
def __str__(self):
"""The string representation of the class"""
return f"{self.shots} shots{' x '+str(self.copies) if self.copies > 1 else ''}"
def __repr__(self):
"""The representation of the class"""
return f"ShotCopies({self.shots} shots x {self.copies})"
def valid_int(s):
"""Returns True if s is a positive integer."""
return isinstance(s, int) and s > 0
def valid_tuple(s):
"""Returns True if s is a tuple of the form (shots, copies)."""
return isinstance(s, tuple) and len(s) == 2 and valid_int(s[0]) and valid_int(s[1])
[docs]class Shots:
"""
A data class that stores shot information.
Args:
shots (Union[None, int, Sequence[int, Tuple[int, int]]]): Raw shot information
Defining shots enables users to specify circuit executions, and the Shots class standardizes
the internal representation of shots. There are three ways to specify shot values:
* The value ``None``
* A positive integer
* A sequence consisting of either positive integers or a tuple-pair of positive integers of the form ``(shots, copies)``
The tuple-pair of the form ``(shots, copies)`` is represented internally by a NamedTuple called
:class:`~ShotCopies`. The first value is the number of shots to execute, and the second value is the
number of times to repeat a circuit with that number of shots.
The ``Shots`` class exposes two properties:
* ``total_shots``, the total number of shots to be executed
* ``shot_vector``, the tuple of :class:`~ShotCopies` to be executed
Instances of this class are static. If an instance is passed to the constructor, that same
instance is returned. If an instance is constructed with a ``None`` value, ``total_shots``
will be ``None``. This indicates analytic execution. A ``Shots`` object created with a
``None`` value is Falsy, while any other value results in a Truthy object:
>>> bool(Shots(None)), bool(Shots(1))
(False, True)
**Examples**
Example constructing a Shots instance with ``None``:
>>> shots = Shots(None)
>>> shots.total_shots, shots.shot_vector
(None, ())
Example constructing a Shots instance with an int:
>>> shots = Shots(100)
>>> shots.total_shots, shots.shot_vector
(100, (ShotCopies(100 shots),))
Example constructing a Shots instance with another instance:
>>> shots = Shots(100)
>>> Shots(shots) is shots
True
Example constructing a Shots instance with a sequence of ints:
>>> shots = Shots([100, 200])
>>> shots.total_shots, shots.shot_vector
(300, (ShotCopies(100 shots x 1), ShotCopies(200 shots x 1)))
Example constructing a Shots instance with a sequence of tuple-pairs:
>>> shots = Shots(((100, 3), (200, 4),))
>>> shots.total_shots, shots.shot_vector
(1100, (ShotCopies(100 shots x 3), ShotCopies(200 shots x 4)))
Example constructing a Shots instance with a sequence of both ints and tuple-pairs.
Note that the first stand-alone ``100`` gets absorbed into the subsequent tuple because the
shot value matches:
>>> shots = Shots((10, 100, (100, 3), (200, 4),))
>>> shots.total_shots, shots.shot_vector
(1210, (ShotCopies(10 shots x 1), ShotCopies(100 shots x 4), ShotCopies(200 shots x 4)))
Example constructing a Shots instance by multiplying an existing one by an int or float:
>>> Shots(100) * 2
Shots(total_shots=200, shot_vector=(ShotCopies(200 shots x 1),))
>>> Shots([7, (100, 2)]) * 1.5
Shots(total_shots=310, shot_vector=(ShotCopies(10 shots x 1), ShotCopies(150 shots x 2)))
One should also note that specifying a single tuple of length 2 is considered two different
shot values, and *not* a tuple-pair representing shots and copies to avoid special behaviour
depending on the iterable type:
>>> shots = Shots((100, 2))
>>> shots.total_shots, shots.shot_vector
(102, (ShotCopies(100 shots x 1), ShotCopies(2 shots x 1)))
>>> shots = Shots(((100, 2),))
>>> shots.total_shots, shots.shot_vector
(200, (ShotCopies(100 shots x 2),))
"""
total_shots: int = None
"""The total number of shots to be executed."""
shot_vector: Tuple[ShotCopies] = None
"""The tuple of :class:`~ShotCopies` to be executed. Each element is of the form ``(shots, copies)``."""
_SHOT_ERROR = ValueError(
"Shots must be a single positive integer, a tuple pair of the form (shots, copies), or a sequence of these types."
)
_frozen = False
def __new__(cls, shots=None):
return shots if isinstance(shots, cls) else object.__new__(cls)
def __setattr__(self, name, value):
if self._frozen:
raise AttributeError(
"Shots is an immutable class. Consider creating a new instance if you need different shot values."
)
return super().__setattr__(name, value)
def __init__(self, shots=None):
if shots is None:
self.total_shots = None
self.shot_vector = ()
elif isinstance(shots, int):
if shots < 1:
raise self._SHOT_ERROR
self.total_shots = shots
self.shot_vector = (ShotCopies(shots, 1),)
elif isinstance(shots, Sequence):
if not all(valid_int(s) or valid_tuple(s) for s in shots):
raise self._SHOT_ERROR
self.__all_tuple_init__([s if isinstance(s, tuple) else (s, 1) for s in shots])
elif isinstance(shots, self.__class__):
return # self already _is_ shots as defined by __new__
else:
raise self._SHOT_ERROR
self._frozen = True
def __copy__(self):
return self
def __deepcopy__(self, memo):
memo[id(self)] = self
return self
def __str__(self):
"""The string representation of the class"""
if not self.has_partitioned_shots:
return f"Shots(total={self.total_shots})"
shot_copy_str = ", ".join([str(sc) for sc in self.shot_vector]) or None
return f"Shots(total={self.total_shots}, vector=[{shot_copy_str}])"
def __repr__(self):
"""The representation of the class"""
return f"Shots(total_shots={self.total_shots}, shot_vector={self.shot_vector})"
def __eq__(self, other):
"""Equality between Shot instances."""
return (
isinstance(other, Shots)
and self.total_shots == other.total_shots
and self.shot_vector == other.shot_vector
)
def __hash__(self):
"""Hash for a given Shot instance."""
return hash(self.shot_vector)
def __iter__(self):
for shot_copy in self.shot_vector:
for _ in range(shot_copy.copies):
yield shot_copy.shots
def __all_tuple_init__(self, shots: Sequence[Tuple]):
res = []
total_shots = 0
current_shots, current_copies = shots[0]
for s in shots[1:]:
if s[0] == current_shots:
current_copies += s[1]
else:
res.append(ShotCopies(current_shots, current_copies))
total_shots += current_shots * current_copies
current_shots, current_copies = s
self.shot_vector = tuple(res + [ShotCopies(current_shots, current_copies)])
self.total_shots = total_shots + current_shots * current_copies
def __bool__(self):
return self.total_shots is not None
def __mul__(self, scalar):
if not isinstance(scalar, (int, float)):
raise TypeError("Can't multiply Shots with non-integer or float type.")
if self.total_shots is None:
return self
scaled_shot_vector = tuple(
ShotCopies(int(i.shots * scalar), i.copies) for i in self.shot_vector
)
return self.__class__(scaled_shot_vector)
def __rmul__(self, scalar):
return self.__mul__(scalar)
@property
def has_partitioned_shots(self):
"""
Evaluates to True if this instance represents either multiple shot
quantities, or the same shot quantity repeated multiple times.
Returns:
bool: whether shots are partitioned
"""
if not self:
return False
return len(self.shot_vector) > 1 or self.shot_vector[0].copies > 1
@property
def num_copies(self):
"""The total number of copies of any shot quantity."""
return sum(s.copies for s in self.shot_vector)
_modules/pennylane/measurements/shots
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