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---
title: ParameterExpression
description: API reference for qiskit.circuit.ParameterExpression
in_page_toc_min_heading_level: 1
python_api_type: class
python_api_name: qiskit.circuit.ParameterExpression
---
<span id="qiskit-circuit-parameterexpression" />
# qiskit.circuit.ParameterExpression
<Class id="qiskit.circuit.ParameterExpression" isDedicatedPage={true} github="https://github.com/qiskit/qiskit/tree/stable/0.16/qiskit/circuit/parameterexpression.py" signature="ParameterExpression(symbol_map, expr)" modifiers="class">
ParameterExpression class to enable creating expressions of Parameters.
Create a new [`ParameterExpression`](#qiskit.circuit.ParameterExpression "qiskit.circuit.ParameterExpression").
Not intended to be called directly, but to be instantiated via operations on other [`Parameter`](qiskit.circuit.Parameter "qiskit.circuit.Parameter") or [`ParameterExpression`](#qiskit.circuit.ParameterExpression "qiskit.circuit.ParameterExpression") objects.
**Parameters**
* **symbol\_map** (*Dict\[*[*Parameter*](qiskit.circuit.Parameter "qiskit.circuit.Parameter")*, \[*[*ParameterExpression*](#qiskit.circuit.ParameterExpression "qiskit.circuit.ParameterExpression")*, float, or int]]*) – Mapping of [`Parameter`](qiskit.circuit.Parameter "qiskit.circuit.Parameter") instances to the `sympy.Symbol` serving as their placeholder in expr.
* **expr** (*sympy.Expr*) – Expression of `sympy.Symbol` s.
### \_\_init\_\_
<Function id="qiskit.circuit.ParameterExpression.__init__" signature="__init__(symbol_map, expr)">
Create a new [`ParameterExpression`](#qiskit.circuit.ParameterExpression "qiskit.circuit.ParameterExpression").
Not intended to be called directly, but to be instantiated via operations on other [`Parameter`](qiskit.circuit.Parameter "qiskit.circuit.Parameter") or [`ParameterExpression`](#qiskit.circuit.ParameterExpression "qiskit.circuit.ParameterExpression") objects.
**Parameters**
* **symbol\_map** (*Dict\[*[*Parameter*](qiskit.circuit.Parameter "qiskit.circuit.Parameter")*, \[*[*ParameterExpression*](#qiskit.circuit.ParameterExpression "qiskit.circuit.ParameterExpression")*, float, or int]]*) – Mapping of [`Parameter`](qiskit.circuit.Parameter "qiskit.circuit.Parameter") instances to the `sympy.Symbol` serving as their placeholder in expr.
* **expr** (*sympy.Expr*) – Expression of `sympy.Symbol` s.
</Function>
## Methods
| | |
| --------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------- |
| [`__init__`](#qiskit.circuit.ParameterExpression.__init__ "qiskit.circuit.ParameterExpression.__init__")(symbol\_map, expr) | Create a new [`ParameterExpression`](#qiskit.circuit.ParameterExpression "qiskit.circuit.ParameterExpression"). |
| [`assign`](#qiskit.circuit.ParameterExpression.assign "qiskit.circuit.ParameterExpression.assign")(parameter, value) | Assign one parameter to a value, which can either be numeric or another parameter expression. |
| [`bind`](#qiskit.circuit.ParameterExpression.bind "qiskit.circuit.ParameterExpression.bind")(parameter\_values) | Binds the provided set of parameters to their corresponding values. |
| [`conjugate`](#qiskit.circuit.ParameterExpression.conjugate "qiskit.circuit.ParameterExpression.conjugate")() | Return the conjugate, which is the ParameterExpression itself, since it is real. |
| [`subs`](#qiskit.circuit.ParameterExpression.subs "qiskit.circuit.ParameterExpression.subs")(parameter\_map) | Returns a new Expression with replacement Parameters. |
## Attributes
| | |
| -------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------- |
| [`parameters`](#qiskit.circuit.ParameterExpression.parameters "qiskit.circuit.ParameterExpression.parameters") | Returns a set of the unbound Parameters in the expression. |
### assign
<Function id="qiskit.circuit.ParameterExpression.assign" signature="assign(parameter, value)">
Assign one parameter to a value, which can either be numeric or another parameter expression.
**Parameters**
* **parameter** ([*Parameter*](qiskit.circuit.Parameter "qiskit.circuit.Parameter")) – A parameter in this expression whose value will be updated.
* **value** (`Union`\[`ParameterExpression`, `float`, `int`]) – The new value to bind to.
**Return type**
`ParameterExpression`
**Returns**
A new expression parameterized by any parameters which were not bound by assignment.
</Function>
### bind
<Function id="qiskit.circuit.ParameterExpression.bind" signature="bind(parameter_values)">
Binds the provided set of parameters to their corresponding values.
**Parameters**
**parameter\_values** (`Dict`) – Mapping of Parameter instances to the numeric value to which they will be bound.
**Raises**
* **CircuitError** –
* If parameter\_values contains Parameters outside those in self. - If a non-numeric value is passed in parameter\_values.
* **ZeroDivisionError** –
* If binding the provided values requires division by zero.
**Return type**
`ParameterExpression`
**Returns**
A new expression parameterized by any parameters which were not bound by parameter\_values.
</Function>
### conjugate
<Function id="qiskit.circuit.ParameterExpression.conjugate" signature="conjugate()">
Return the conjugate, which is the ParameterExpression itself, since it is real.
**Return type**
`ParameterExpression`
</Function>
### parameters
<Attribute id="qiskit.circuit.ParameterExpression.parameters">
Returns a set of the unbound Parameters in the expression.
**Return type**
`Set`
</Attribute>
### subs
<Function id="qiskit.circuit.ParameterExpression.subs" signature="subs(parameter_map)">
Returns a new Expression with replacement Parameters.
**Parameters**
**parameter\_map** (`Dict`) – Mapping from Parameters in self to the ParameterExpression instances with which they should be replaced.
**Raises**
**CircuitError** –
* If parameter\_map contains Parameters outside those in self. - If the replacement Parameters in parameter\_map would result in a name conflict in the generated expression.
**Return type**
`ParameterExpression`
**Returns**
A new expression with the specified parameters replaced.
</Function>
</Class>
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