title: From string to float with argv in python
body: <p>I can't convert a string passed throug command line to a function to float. </p>
  
  <p>I'll explain better. 
  I have this function who takes two arguments, the second one is a float</p>
  
  <pre><code>def function():
     first_param = sys.argv[1]
     second_param = float(sys.argv[2])
  </code></pre>
  
  <p>Then I have this other function who calls the first one in a software container</p>
  
  <pre><code>def callFunction(first_arg, second_arg):
     cmd = 'docker run --rm -v pathFunction:/home/fenics/shared -w /home/fenics/shared quay.io/fenicsproject/stable "python2 function.py ' + first_arg + str(second_arg)
     process = subprocess.Popen(cmd, shell=True)
  </code></pre>
  
  <p>When I call:</p>
  
  <pre><code>callFunction("some_string",0.02)
  </code></pre>
  
  <p>it returns me an error in function at the line at whick I try the conversione to float saying:
  could not convert string to float : shell </p>
  
  <p>UPDATE 
  I've found that the problem is that the first string I'm passing is a path with some spaces in it. Something like: 
  some_string = C:\blabla\my directory\file.txt" 
  with a space between 'my' and 'directory'. I can't change the path, do you know how could I fix it?</p>