numpy

In the previous blog post, we introduced the concept of a ‘remote laboratory’, which would enable users to access the various features of the PSLab via the internet. Many aspects of the project were worked upon, which also involved creation of a web-app using EmberJS that enables users to create accounts , sign in, and prepare Python programs to be sent to the server for execution. A backend APi server based on Python-flask was also developed to handle these tasks, and maintain a postgresql database using sqlalchemy . The following screencast shows the basic look and feel of the proposed remote lab running in a web browser. This blog post will deal with implementing a way for the remote user to submit a simple function string, such as get_voltage(‘CH1’), and retrieve the results from the server. There are three parts to this: Creating a dictionary of the functions available in the sciencelab instance. The user will only be allowed access to these functions remotely, and we may protect some functions as the initialization and destruction routines by blocking them from the remote user Creating an API method to receive a form containing the function string, execute the corresponding function from the dictionary, and reply with JSON data Testing the API using the postman chrome extension Creating a dictionary of functions : The function dictionary maps function names against references to the actual functions from an instance of PSL.sciencelab . A simple dictionary containing just the get_voltage function can be generated in the following way: from PSL import sciencelab I=sciencelab.connect() functionList = {'get_voltage':I.get_voltage} This dictionary is then used with the eval method in order to evaluate a function string: result = eval('get_voltage('CH1')',functionList) print (result) 0.0012 A more efficient way to create this list is to use the inspect module, and automatically extract all the available methods into a dictionary functionList = {} for a in dir(I): attr = getattr(I, a) if inspect.ismethod(attr) and a!='__init__': functionList[a] = attr In the above, we have made a dictionary of all the methods except __init__ This approach can also be easily extrapolated to automatically generate a dictionary for inline documentation strings which can then be passed on to the web app. Creating an API method to execute submitted function strings We create an API method that accepts a form containing the function string and option that specifies if the returned value is to be formatted as a string or JSON data. A special case arises for numpy arrays which cannot be directly converted to JSON, and the toList function must first be used for them. @app.route('/evalFunctionString',methods=['POST']) def evalFunctionString(): if session.get('user'): _stringify=False try: _user = session.get('user')[1] _fn = request.form['function'] _stringify = request.form.get('stringify',False) res = eval(_fn,functionList) except Exception as e: res = str(e) #dump string if requested. Otherwise json array if _stringify: return json.dumps({'status':True,'result':str(res),'stringified':True}) else: #Try to simply convert the results to json try: return json.dumps({'status':True,'result':res,'stringified':False}) # If that didn't work, it's due to the result containing numpy arrays. except Exception as e: #try to convert the…