Add SportranBinaryFile

Working on #37.
A first draft of SportranBinaryFile.
The useful storable attributes (input_parameters, settings, current,
current_resampled, output_results) should be further defined/corrected.

TODO:
- Define proper data structures: SportranInput, SportranSettings,
SportranOutput, ...
  these can be seen as input/outputs of a "Workflow".
  A workflow for example is defined in analysis.py
- Define functions that collect all the data useful to save the current
calculation/namespace and dumps it into a SportranBinaryFile.
- Define functions that extract and use the data of a SportranBinaryFile
  to restore a calculation/data namespace.

thermocepstrum/i_o/binary.py

@@ -0,0 +1,134 @@
+# -*- coding: utf-8 -*-
+
+from thermocepstrum.utils.attributedict import AttributeDict
+from thermocepstrum.current import Current
+import pickle
+
+__all__ = ('SportranBinaryFile', 'SportranInput', 'SportranOutput', 'SportranSettings')
+
+
+def multi_pickle_dump(self, filename, **objs):
+    # dump a dictionary of all the passed objects
+    pickle.dump(objs, open(filename, 'wb'))
+
+
+def multi_pickle_load(self, filename):
+    # return a dictionary of all the stored objects
+    return pickle.load(open(filename, 'rb'))
+
+
+class SportranInput(AttributeDict):
+
+    pass
+
+
+class SportranOutput(AttributeDict):
+
+    pass
+
+
+class SportranSettings(AttributeDict):
+
+    pass
+
+
+class SportranBinaryFile():
+    """
+    A SporTran Binary File object, that stores information about a SporTran calculation, its inputs, data, and outputs.
+    The data stored can be used to restore a calculation that was previously run.
+
+    Attributes:
+        input_parameters    a SportranInput object, the input parameters of the calculation
+        settings            a SportranSettings object, the calculation settings
+        current             a Current object, the original current
+        current_resampled   a Current object, the current obtained by resampling current
+        output_results      a SportranOutput object, the calculation outputs
+
+    Methods:
+        :classmethod: load(filename)
+        :method: dump(filename)
+    """
+
+    _storable_attrs = ('input_parameters', 'settings', 'current', 'current_resampled', 'output_results')
+
+    def __init__(self, **kwargs):
+        for key in self._storable_attrs:
+            self.__setattr__(key, kwargs.pop(key, None))
+        if kwargs:
+            raise ValueError('Keys {} are not valid.'.format(kwargs.keys()))
+
+    @classmethod
+    def load(cls, filename):
+        """Load SporTran data from a binary file."""
+        return cls(**multi_pickle_load(filename))
+
+    def dump(self, filename):
+        """Dump SporTran data to a binary file."""
+        multi_pickle_dump(filename, **{key: self.key for key in self._storable_attrs})
+        print(f'Binary file "{filename}" successfully created, with the following data:')
+        print([key for key in self._storable_attrs if key is not None])
+
+    @property
+    def input_parameters(self):
+        return self._input_parameters
+
+    @input_parameters.setter
+    def input_parameters(self, value):
+        if value is None:
+            self._input_parameters = None
+        elif isinstance(value, SportranInput):
+            self._input_parameters = value
+        else:
+            raise TypeError()
+
+    @property
+    def settings(self):
+        return self._settings
+
+    @settings.setter
+    def settings(self, value):
+        if value is None:
+            self._settings = None
+        elif isinstance(value, SportranSettings):
+            self._settings = value
+        else:
+            raise TypeError()
+
+    @property
+    def current(self):
+        return self._current
+
+    @current.setter
+    def current(self, value):
+        if value is None:
+            self._current = None
+        elif isinstance(value, Current):
+            self._current = value
+        else:
+            raise TypeError()
+
+    @property
+    def current_resampled(self):
+        return self._current_resampled
+
+    @current_resampled.setter
+    def current_resampled(self, value):
+        if value is None:
+            self._current_resampled = None
+        elif isinstance(value, Current):
+            self._current_resampled = value
+        else:
+            raise TypeError()
+
+    @property
+    def output_results(self):
+        return self._output_results
+
+    @output_results.setter
+    def output_results(self, value):
+        if value is None:
+            self._output_results = None
+        elif isinstance(value, SportranOutput):
+            self._output_results = value
+        else:
+            raise TypeError()