title: PyYAML shows "ScannerError: mapping values are not allowed here" in my unittest
body: <p>I am trying to test a number of Python 2.7 classes using unittest.</p>
  
  <p>Here is the exception:</p>
  
  <pre><code>ScannerError: mapping values are not allowed here
      in "&lt;unicode string&gt;", line 3, column 32:
              ... file1_with_path: '../../testdata/concat1.csv'
  </code></pre>
  
  <p>Here is the example the error message relates to:</p>
  
  <pre><code>class TestConcatTransform(unittest.TestCase):
  
  def setUp(self):
      filename1 = os.path.dirname(os.path.realpath(__file__)) + '/../../testdata/concat1.pkl'
      self.df1 = pd.read_pickle(filename1)
      filename2 = os.path.dirname(os.path.realpath(__file__)) + '/../../testdata/concat2.pkl'
      self.df2 = pd.read_pickle(filename2)
  
      self.yamlconfig =  u'''
          --- !ConcatTransform
          file1_with_path: '../../testdata/concat1.csv'
          file2_with_path: '../../testdata/concat2.csv'
          skip_header_lines: [0]
          duplicates: ['%allcolumns']
          outtype: 'dataframe'
          client: 'testdata'
          addcolumn: []
      '''
      self.testconcat = yaml.load(self.yamlconfig)
  </code></pre>
  
  <p>What is the the problem?</p>
  
  <p>Something not clear to me is that the directory structure I have is:</p>
  
  <pre><code>app
  app/etl
  app/tests
  </code></pre>
  
  <p>The <code>ConcatTransform</code> is in <code>app/etl/concattransform.py</code> and <code>TestConcatTransform</code> is in <code>app/tests</code>. I import <code>ConcatTransform</code> into the <code>TestConcatTransform</code> unittest with this import:</p>
  
  <pre><code>from app.etl import concattransform
  </code></pre>
  
  <p>How does PyYAML associate that class with the one defined in yamlconfig?</p>