title: Unpickling dictionary that holds pandas dataframes throws AttributeError: 'Dataframe' object has no attribute '_data'
body: <p>I have a class that performs analyses and attaches the results, which are pandas dataframes, as object attributes:</p>
  <pre><code>&gt;&gt;&gt; print(test.image.locate_DF)
                y          x       mass  ...    raw_mass        ep  frame
  0     60.177142  59.788709  33.433414  ...  242.080256       NaN      0
  1     60.651991  59.773904  33.724308  ...  242.355784       NaN      1
  2     60.790437  60.190234  31.117164  ...  236.276671       NaN      2
  3     60.771933  60.048123  33.558372  ...  240.981395       NaN      3
  4     60.251282  59.775139  31.881009  ...  239.239022       NaN      4
  ...         ...        ...        ...  ...         ...       ...    ...
  7212  68.186380  76.477449  18.122817  ...  176.523091       NaN   9410
  7213  68.764444  76.574091  17.486454  ...  173.448306       NaN   9415
  7214  68.191152  76.473477  17.402975  ...  172.848119  0.868326   9429
  7215  67.034103  76.025885  17.010951  ...  170.928067 -0.600854   9431
  7216  68.583276  75.309592  17.852992  ...  178.271558       NaN   9432
  </code></pre>
  <p>Subsequently, I save all the important object attributes in a dictionary, and pickle it for later use:</p>
  <pre><code>def save_parameters(self, filepath):
          
          param_dict = {}
  
      try:
              self.image.locate_DF
          except AttributeError:
              pass
          else:
              param_dict['optical_locate_DF'] = self.image.locate_DF
  
      with open(filepath, 'wb') as handle:
              pickle.dump(param_dict, handle, 5)
  </code></pre>
  <p>When trying to load that pickled file, I have no problem at all, the dataframe loads perfectly:</p>
  <pre><code>&gt;&gt;&gt; test.save_parameters('test.pickle')
  &gt;&gt;&gt; with open('test.pickle', 'rb') as handle:
  ...     result = pickle.load(handle)
  ...
  &gt;&gt;&gt; print(result.keys())
  dict_keys(['optical_path', 'optical_feature_diameter', 'optical_feature_minmass', 'optical_locate_DF', 'electrical_path', 'electrical_raw_data', 'electrical_processed_data', 'electrical_mean_voltage'])
  &gt;&gt;&gt; print(result['optical_locate_DF'])
                y          x       mass  ...    raw_mass        ep  frame
  0     60.177142  59.788709  33.433414  ...  242.080256       NaN      0
  1     60.651991  59.773904  33.724308  ...  242.355784       NaN      1
  2     60.790437  60.190234  31.117164  ...  236.276671       NaN      2
  3     60.771933  60.048123  33.558372  ...  240.981395       NaN      3
  4     60.251282  59.775139  31.881009  ...  239.239022       NaN      4
  ...         ...        ...        ...  ...         ...       ...    ...
  7212  68.186380  76.477449  18.122817  ...  176.523091       NaN   9410
  7213  68.764444  76.574091  17.486454  ...  173.448306       NaN   9415
  7214  68.191152  76.473477  17.402975  ...  172.848119  0.868326   9429
  7215  67.034103  76.025885  17.010951  ...  170.928067 -0.600854   9431
  7216  68.583276  75.309592  17.852992  ...  178.271558       NaN   9432
  
  [7217 rows x 9 columns]
  </code></pre>
  <p>However, after running my analysis on a bunch of these files on a hpc, and then trying to open that same pickled file (it's named differently now but it's the same file as shown above, with the same analysis performed on it), I get thrown an attribute error by pandas. It states that the dataframe has no '_data' attribute. The dictionary has the same keys and the keys that are not a dataframe are printed without any issues:</p>
  <pre><code>&gt;&gt;&gt; resultfile = '../results/diam_15_minmass_17_dist_50_mem_5000_tracklength_500/R9_DNA_50mV_001.pickle'
  &gt;&gt;&gt; with open(resultfile, 'rb') as handle:
  ...     result = pickle.load(handle)
  ...
  &gt;&gt;&gt; print(result.keys())
  dict_keys(['optical_path', 'optical_feature_diameter', 'optical_feature_minmass', 'optical_locate_DF', 'optical_tracking_distance', 'optical_tracking_memory', 'optical_tracking_DF', 'optical_kinetics_DF', 'electrical_path', 'electrical_raw_data', 'electrical_processed_data', 'electrical_mean_voltage'])
  &gt;&gt;&gt; print(result['optical_locate_DF'])
  Traceback (most recent call last):
    File &quot;&lt;stdin&gt;&quot;, line 1, in &lt;module&gt;
    File &quot;/Users/stevenvanuytsel/miniconda3/envs/simultaneous_measurements/lib/python3.8/site-packages/pandas/core/frame.py&quot;, line 680, in __repr__
      self.to_string(
    File &quot;/Users/stevenvanuytsel/miniconda3/envs/simultaneous_measurements/lib/python3.8/site-packages/pandas/core/frame.py&quot;, line 801, in to_string
      formatter = fmt.DataFrameFormatter(
    File &quot;/Users/stevenvanuytsel/miniconda3/envs/simultaneous_measurements/lib/python3.8/site-packages/pandas/io/formats/format.py&quot;, line 593, in __init__
      self.max_rows_displayed = min(max_rows or len(self.frame), len(self.frame))
    File &quot;/Users/stevenvanuytsel/miniconda3/envs/simultaneous_measurements/lib/python3.8/site-packages/pandas/core/frame.py&quot;, line 1041, in __len__
      return len(self.index)
    File &quot;/Users/stevenvanuytsel/miniconda3/envs/simultaneous_measurements/lib/python3.8/site-packages/pandas/core/generic.py&quot;, line 5270, in __getattr__
      return object.__getattribute__(self, name)
    File &quot;pandas/_libs/properties.pyx&quot;, line 63, in pandas._libs.properties.AxisProperty.__get__
    File &quot;/Users/stevenvanuytsel/miniconda3/envs/simultaneous_measurements/lib/python3.8/site-packages/pandas/core/generic.py&quot;, line 5270, in __getattr__
      return object.__getattribute__(self, name)
  AttributeError: 'DataFrame' object has no attribute '_data'
  </code></pre>
  <p>I've looked into the pickle manual, and through a bunch of SO questions, but I can't seem to find out what is going wrong here. Does anyone have an idea how to fix this, and also whether I can still access that data?</p>