# Getting Started with Python and the Quantum Development Kit

The qsharp package for Python provides interoperability with the Quantum Development Kit and with the Q# language, making it easy to simulate Q# operations and functions from within Python.

## Pre-requisites

To get started with the qsharp package, you'll need the following prerequisites:

• IQ#.
• Python 3.6 or later,

Make sure you have followed the installation steps in the getting started guide for IQ#.

To install Python, we recommend using the Anaconda distribution of Python. Please see https://www.anaconda.com/distribution/ for more details.

## Installation

Install qsharp using pip:

pip install qsharp --upgrade


You will also need to explicitly install the iqsharp kernel using this command:

dotnet iqsharp install


## Usage

The qsharp package finds all the files under the current working folder with a .qs extension and compiles them.

To get started, create a new Quantum.qs file with the following content:

namespace Microsoft.Samples
{
open Microsoft.Quantum.Intrinsic;
open Microsoft.Quantum.Canon;

operation HelloQ() : Result
{
Message($"Hello from quantum world!"); return Zero; } }  Note All .qs files under the current working folder need to correctly compile before any of the operations can be used from Python. To call the HelloQ Q# operation from Python, first import the qsharp module: import qsharp  After this, Q# namespaces can be imported as Python packages, for example: from Microsoft.Samples import HelloQ  ### Simulation Once imported, to simulate a Q# operation invoke it's simulate method: If the Q# operation returns a value, the corresponding value is returned from the simulate method. If the method uses Message the messages will be displayed on the console, for example: >>> HelloQ.simulate() Hello from quantum world! 0  A .qs file may contain multiple operations, for example we could add the following code to Quantum.qs:  /// # Summary: /// A more sophisticated operation that shows how to /// specify parameters, instantiate qubits, and return values. operation HelloAgain(count: Int, name: String) : Result[] { Message($"Hello {name} again!");

mutable r = new Result[count];
using (q = Qubit()) {
for (i in 1..count) {
ApplyIf(X, i == 2, q);
set r w/= (i - 1) <- M(q);
Reset(q);
}
}

return r;
}


File changes are automatically picked up when the Python environment is restarted. To pick up the changes immediately without having to restart Python, you can invoke reload method:

>>> qsharp.reload()
>>> from Microsoft.Samples import HelloAgain


If the Q# operation expects parameters, include them as named parameters to the simulate method:

>>> HelloAgain.simulate(count=3, name="old friend")
Hello "old friend" again!
[0, 1, 0]


### Resources Estimation

On top of simulation, you can also do quantum resources estimation including the count of primitive operations used by the algorithm and the number of required qubits. For this, invoke the estimate_resources method on the operation which returns a dictionary with the list of estimated resources:

>>> HelloAgain.estimate_resources(count=3, name="resources")
Hello "resources" again!
{'CNOT': 0, 'QubitClifford': 1, 'R': 0, 'Measure': 6, 'T': 0, 'Depth': 0, 'Width': 1, 'BorrowedWidth': 0}


The list of metrics and their description can be found in the resources estimator documentation.

### Quantum Libraries

All .qs files can automatically use all standard operations defined in the Quantum Development Kit. To import operations defined in other libraries, their corresponding nuget package needs to be added first. In particular, to use the operations from the chemistry library you need to add the Microsoft.Quantum.Chemistry package to qsharp.

>>>import qsharp

If your .qs uses operations from the chemistry library, qsharp will need to be reloaded to pick up the new references:
>>> qsharp.reload()