In the following code, some basic attributes of the virtual machine are set before it is created. In fact, there are a large number of attributes specific to a virtual machine that can be set to control how the virtual machine is configured. Here the most basic attributes have been selected to create a virtual machine using Xen para-virtualization with its configuration located on the repository called 'MyRepository'. The virtual machine is also attached to the server pool called 'MyServerPool'.

...
repo_id=get_id_from_name(s,baseUri,'Repository','MyRepository')
sp_id=get_id_from_name(s,baseUri,'ServerPool','MyServerPool')
data={
        'name': 'MyVirtualMachine',
        'description': 'A virtual machine created using the REST API',
        'vmDomainType': 'XEN_PVM',
        'repositoryId': repo_id,
        'serverPoolId': sp_id,
    }
uri='{base}/Vm'.format(base=baseUri)
r=s.post(uri,data=json.dumps(data))
job=r.json()
# wait for the job to complete
vm_id=wait_for_job(job['id']['uri'],s)

The VM created in this example is very simple and few attributes have been configured. If you intend to create virtual machines like this, it is worthwhile referring to the API documentation to discover what attributes can be set to fully configure your virtual machine.