title: TypeError: coercing to Unicode, need string or buffer, NoneType found
body: <p>Currently writing a function for a program and one component is to search whether a single variables are being used within a python file. </p>
  
  <p>FUNCTION:</p>
  
  <pre><code>def SINGLE_CHAR_VAR(python_filename):
      file = open(python_filename)
      lines = [0]
      SINGLE_CHAR_VAR = []
      for line in file:
          stripped = line.strip('\n\r')
          lines.append(stripped)
  
      from utils import vars_indents
      variable_list = (vars_indents(python_filename))[0]
      for i in range(1, len(variable_list)):
          if len(variable_list[i][0][0]) == 1:
              SINGLE_CHAR_VAR.append(['SINGLE_CHAR_VAR', i, variable_list[i][0][1], variable_list[i][0][0], lines[i]])      
      return SINGLE_CHAR_VAR​
  </code></pre>
  
  <p>When i used the function by itself - the function works properly.
  However when i call upon the program as a whole - i get the following error message:</p>
  
  <pre><code>Traceback (most recent call last):
    File "&lt;web session&gt;", line 1, in &lt;module&gt;
    File "lint_2.py", line 141, in lint
      sorted_error_list = sorted_list(list_of_file_errors)
    File "lint_2.py", line 84, in sorted_list
      error_list = total_error_list(python_filename)
    File "lint_2.py", line 65, in total_error_list
      single_char_var_list = SINGLE_CHAR_VAR(python_filename)
    File "lint_2.py", line 33, in SINGLE_CHAR_VAR
      file = open(python_filename)
  TypeError: coercing to Unicode: need string or buffer, NoneType found
  </code></pre>
  
  <p>I have absolutely no idea - where I am going wrong - any help would be very, very, very cherished!!!</p>
  
  <p>thanks. </p>