title: sqlalchemy.exc.InvalidRequestError: Mapper '...' has no property '...'
body: <p>I have two classes, <code>TrialIdentifier</code> and <code>TimeCourse</code></p>
  
  <p>TimeCourse has an instance variable containing a TrialIdentifier, and I am trying to setup a foreign key relationship between the two.</p>
  
  <p>in TrialIdentifier</p>
  
  <pre><code>__tablename__ = 'trial_identifiers'
  
  relationships = relationship('TimeCourse', 
                               back_populates = 'trial_identifier', uselist = False)
  </code></pre>
  
  <p>in TimeCourse</p>
  
  <pre><code>__tablename__ = 'time_course'
  
  trial_identifier_id = Column(Integer, ForeignKey('trial_identifiers.id'))
  trial_identifier = relationship('TrialIdentifier', back_populates = 'relationships')`
  </code></pre>
  
  <p>If I name the variable <code>trial_identifier</code> in <code>TimeCourse</code> the following error is thrown:</p>
  
  <pre><code>sqlalchemy.exc.InvalidRequestError: Mapper 'Mapper|TimeCourse|time_course' has no property 'trial_identifier'
  </code></pre>
  
  <p>If I name it anything else, everything works fine. The entire package is built on the <code>TimeCourse().trial_identifier</code> so I would like to avoid refactoring it if possible. Or at least understand this behavior.</p>