DataModelDict 0.9.9
Class allowing for data models equivalently represented as Python dictionaries, JSON, and XML
Keywords: json,xml,dictionary

=============
DataModelDict
=============

Introduction
------------

The DataModelDict class is used for handling data models that have equivalent
representations in XML, JSON, and Python.  Constructing data models in this
way is convenient as it supports compatibility across different software
tools, such as different types of databases.

The DataModelDict class:

- is a child of OrderedDict,
- has methods for converting to/from XML and JSON, 
- has methods for searching through elements, and
- has methods that help with constructing and interacting with compliant data
  models.

Setup
-----

The code has no requirements that limit which systems it can be used on, i.e.
it should work on Linux, Mac and Windows computers.

The latest release can be installed using pip::

    pip install DataModelDict

The code and all documentation is hosted on GitHub and can be directly
downloaded at `https://github.com/usnistgov/DataModelDict`_.

.. _https://github.com/usnistgov/DataModelDict: 
   https://github.com/usnistgov/DataModelDict

Conversions
-----------

Some considerations need to be taken into account for designing data models
that allow for exact reversible transformations between the three formats:

- Valid, full XML requires that there is exactly one root element.  In other
  words, the top-level DataModelDict of a data model   can have only one key.
- Do not use lists of lists for representing data.  The XML conversions are
  only reversible for lists of values or lists of dictionaries.  Future
  updates may allow this.
- Avoid using XML attributes if possible.  While the XML conversions do
  reversibly handle attributes, it complicates the Python and JSON
  representations.
- Embedded XML content, i.e. "text with <embed>embedded</embed> content",
  might not be reversible:

    - If this is in a Python/JSON value, converting to XML gives "text with
      &amp;lt;embed&amp;gt;embedded&amp;lt;/embed&amp;gt; content". This is
      reversible.
    - If this is an XML text field, parsing to Python pulls the embedded
      elements out of the text, which is not reversible!

- XML subelements of the same name within an element should be given
  consecutively.  When parsed, all values of subelements of the same name are
  collected together in a list.  This will alter the original order of
  subelements if matching names were not originally consecutive. 

Conversion from Python to JSON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Python-JSON conversions use the standard Python JSON library.  In
converting from Python to JSON, all elements of the DataModelDict must be an
instance of a supported data type.

================  =========
Python            JSON     
================  =========
dict              object   
list, tuple       array    
str               string   
int, float        number   
True              true     
False             false    
None              null     
np.nan            NaN      
np.inf            Infinity 
-np.inf           -Infinity
================  =========

As DataModelDict is a child of OrderedDict, it registers as being an instance
of dict. Any other objects would first need to be converted to one of these
types, e.g. a numpy array would need to be converted to a list.

Conversion from Python to XML
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Python-XML conversions use the xmltodict Python package. The XML content
is constructed based on the Python data types.

================  ================
Python            XML             
================  ================
dict              subelement      
list, tuple       repeated element
str               text            
int, float        repr(val)       
True              'true'          
False             'false'         
None              ''              
np.nan            'NaN'           
np.inf            'Infinity'      
-np.inf           '-Infinity'     
================  ================

Some characters in the XML text fields will also be converted to avoid
conflicts.

- XML limited characters such as <, > and & are converted to their
  HTML entities.
- \\n, \\t, \\r are converted to \\\\n, \\\\t, and \\\\r

Any dictionary keys starting with '@' will be converted into XML attributes,
and the dictionary key '#text' is interpreted as the text value of the
element.

Conversion from JSON to Python
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Python-JSON conversions use the standard Python JSON library.  In
converting from JSON to Python, the conversions of types is straight-forward.

=============  =============
JSON           Python       
=============  =============
object         DataModelDict
array          list         
string         str          
number (int)   int          
number (real)  float        
true           True         
false          False        
null           None         
NaN            np.nan       
Infinity       np.inf       
-Infinity      -np.inf      
=============  =============

Conversion from XML to Python
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Python-XML conversions use the xmltodict Python package.  The text fields
will be interpreted based on the following sequential tests:

========================================  ========
XML text                                  Python  
========================================  ========
text == 'True' or 'true'                  True    
text == 'False' or 'false'                False   
text == ''                                None    
text == 'NaN'                             np.nan  
text == 'Infinity'                        np.inf  
text == '-Infinity'                       -np.inf 
try int(text) and text == str(int(text))  int     
try float(text)                           float   
otherwise                                 str     
========================================  ========

The int conversion test was updated for version 0.9.8 to check that the values
can reversably be changed back into a str.  This is necessary to properly
handle values, such as journal page numbers, that may contain leading zeroes.

The reverse conversions are done for the special characters mentioned in the
Conversion from Python to XML section above.

Any 'attr' attribute fields are converted to elements named '\@attr' and
corresponding '#text' elements are created if needed.

Code Documentation
------------------

=============
DataModelDict
=============

Introduction
------------

The DataModelDict class is used for handling data models that have equivalent
representations in XML, JSON, and Python.  Constructing data models in this
way is convenient as it supports compatibility across different software
tools, such as different types of databases.

The DataModelDict class:

- is a child of OrderedDict,
- has methods for converting to/from XML and JSON, 
- has methods for searching through elements, and
- has methods that help with constructing and interacting with compliant data
  models.

Setup
-----

The code has no requirements that limit which systems it can be used on, i.e.
it should work on Linux, Mac and Windows computers.

The latest release can be installed using pip::

    pip install DataModelDict

The code and all documentation is hosted on GitHub and can be directly
downloaded at `https://github.com/usnistgov/DataModelDict`_.

.. _https://github.com/usnistgov/DataModelDict: 
   https://github.com/usnistgov/DataModelDict

Conversions
-----------

Some considerations need to be taken into account for designing data models
that allow for exact reversible transformations between the three formats:

- Valid, full XML requires that there is exactly one root element.  In other
  words, the top-level DataModelDict of a data model   can have only one key.
- Do not use lists of lists for representing data.  The XML conversions are
  only reversible for lists of values or lists of dictionaries.  Future
  updates may allow this.
- Avoid using XML attributes if possible.  While the XML conversions do
  reversibly handle attributes, it complicates the Python and JSON
  representations.
- Embedded XML content, i.e. "text with <embed>embedded</embed> content",
  might not be reversible:

    - If this is in a Python/JSON value, converting to XML gives "text with
      &amp;lt;embed&amp;gt;embedded&amp;lt;/embed&amp;gt; content". This is
      reversible.
    - If this is an XML text field, parsing to Python pulls the embedded
      elements out of the text, which is not reversible!

- XML subelements of the same name within an element should be given
  consecutively.  When parsed, all values of subelements of the same name are
  collected together in a list.  This will alter the original order of
  subelements if matching names were not originally consecutive. 

Conversion from Python to JSON
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Python-JSON conversions use the standard Python JSON library.  In
converting from Python to JSON, all elements of the DataModelDict must be an
instance of a supported data type.

================  =========
Python            JSON     
================  =========
dict              object   
list, tuple       array    
str               string   
int, float        number   
True              true     
False             false    
None              null     
np.nan            NaN      
np.inf            Infinity 
-np.inf           -Infinity
================  =========

As DataModelDict is a child of OrderedDict, it registers as being an instance
of dict. Any other objects would first need to be converted to one of these
types, e.g. a numpy array would need to be converted to a list.

Conversion from Python to XML
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Python-XML conversions use the xmltodict Python package. The XML content
is constructed based on the Python data types.

================  ================
Python            XML             
================  ================
dict              subelement      
list, tuple       repeated element
str               text            
int, float        repr(val)       
True              'true'          
False             'false'         
None              ''              
np.nan            'NaN'           
np.inf            'Infinity'      
-np.inf           '-Infinity'     
================  ================

Some characters in the XML text fields will also be converted to avoid
conflicts.

- XML limited characters such as <, > and & are converted to their
  HTML entities.
- \\n, \\t, \\r are converted to \\\\n, \\\\t, and \\\\r

Any dictionary keys starting with '@' will be converted into XML attributes,
and the dictionary key '#text' is interpreted as the text value of the
element.

Conversion from JSON to Python
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Python-JSON conversions use the standard Python JSON library.  In
converting from JSON to Python, the conversions of types is straight-forward.

=============  =============
JSON           Python       
=============  =============
object         DataModelDict
array          list         
string         str          
number (int)   int          
number (real)  float        
true           True         
false          False        
null           None         
NaN            np.nan       
Infinity       np.inf       
-Infinity      -np.inf      
=============  =============

Conversion from XML to Python
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Python-XML conversions use the xmltodict Python package.  The text fields
will be interpreted based on the following sequential tests:

========================================  ========
XML text                                  Python  
========================================  ========
text == 'True' or 'true'                  True    
text == 'False' or 'false'                False   
text == ''                                None    
text == 'NaN'                             np.nan  
text == 'Infinity'                        np.inf  
text == '-Infinity'                       -np.inf 
try int(text) and text == str(int(text))  int     
try float(text)                           float   
otherwise                                 str     
========================================  ========

The int conversion test was updated for version 0.9.8 to check that the values
can reversably be changed back into a str.  This is necessary to properly
handle values, such as journal page numbers, that may contain leading zeroes.

The reverse conversions are done for the special characters mentioned in the
Conversion from Python to XML section above.

Any 'attr' attribute fields are converted to elements named '\@attr' and
corresponding '#text' elements are created if needed.

Class Documentation
-------------------

**class DataModelDict.DataModelDict(*args, kwargs)**

   Bases: ``collections.OrderedDict``

   Class for handling json/xml equivalent data structures.

   **append(key, value)**

      Adds a value for element key by either adding key to the
      dictionary or appending the value as a list to any current
      value.

      :Parameters:
         * **key** (*str*) â€“ The dictionary key.

         * **value** â€“ The value to add to the dictionary key.  If
            key exists, the element is converted to a list if needed
            and value is appended.

   **aslist(key)**

      Gets the value of a dictionary key as a list.  Useful for
      elements whose values may or may not be lists.

      :Parameters:
         **key** (*str*) â€“ Dictionary key

      :Returns:
         The dictionaryâ€™s element value or [value] depending on if it
         already is a list.

      :Return type:
         list

   **find(key, yes={}, no={})**

      Return the value of a subelement at any level uniquely
      identified by the specified conditions.

      :Parameters:
         * **key** (*str*) â€“ Dictionary key to search for.

         * **yes** (*dict*) â€“ Key-value terms which the subelement
            must have to be considered a match.

         * **no** (*dict*) â€“ Key-value terms which the subelement
            must not have to be considered a match.

      :Returns:
         The value of the uniquely identified subelement.

      :Return type:
         any

      :Raises:
         **ValueError** â€“ If exactly one matching subelement is not
         identified.

   **finds(key, yes={}, no={})**

      Finds the values of all subelements at any level identified by
      the specified conditions.

      :Parameters:
         * **key** (*str*) â€“ Dictionary key to search for.

         * **yes** (*dict*) â€“ Key-value terms which the subelement
            must have to be considered a match.

         * **no** (*dict*) â€“ Key-value terms which the subelement
            must not have to be considered a match.

      :Returns:
         The values of any matching subelements.

      :Return type:
         list

   **iteraslist(key)**

      Iterates through the values of a dictionary key.  Useful for
      elements whose values may or may not be lists.

      :Parameters:
         **key** (*str*) â€“ Dictionary key

      :Yields:
         *any* â€“ The dictionaryâ€™s value or each element in value if
         value is a list.

   **iterfinds(key, yes={}, no={})**

      Iterates over the values of all subelements at any level
      identified by the specified conditions.

      :Parameters:
         * **key** (*str*) â€“ Dictionary key to search for.

         * **yes** (*dict*) â€“ Key-value terms which the subelement
            must have to be considered a match.

         * **no** (*dict*) â€“ Key-value terms which the subelement
            must not have to be considered a match.

      :Yields:
         *any* â€“ The values of any matching subelements.

   **iterpaths(key, yes={}, no={})**

      Iterates over the path lists to all elements at any level
      identified by the specified conditions.

      :Parameters:
         * **key** (*str*) â€“ Dictionary key to search for.

         * **yes** (*dict*) â€“ Key-value terms which the subelement
            must have to be considered a match.

         * **no** (*dict*) â€“ Key-value terms which the subelement
            must not have to be considered a match.

      :Yields:
         *list of str* â€“ The path lists to any matching subelements.

   **itervaluepaths()**

      Iterates over path lists to all value elements at any level.

      :Yields:
         *list* â€“ The path lists to all value subelements.

   **json(fp=None, *args, kwargs)**

      Converts the DataModelDict to JSON content.

      :Parameters:
         * **fp** (*file-like object or None, optional*) â€“ An
            open file to write the content to.  If None (default),
            then the content is returned as a str.

         * ***args** (*any*) â€“ Any other positional arguments
            accepted by json.dump(s)

         * ****kwargs** (*any*) â€“ Any other keyword arguments
            accepted by json.dump(s)

      :Returns:
         The JSON content (only returned if fp is None).

      :Return type:
         str, optional

   **load(model, format=None)**

      Read in values from a json/xml string or file-like object.

      :Parameters:
         * **model** (*str or file-like object*) â€“ The XML or
            JSON content to read.  This is allowed to be either a file
            path, a string representation, or an open file-like object
            in byte mode.

         * **format** (*str or None, optional*) â€“ Allows for
            the format of the content to be explicitly stated (â€˜xmlâ€™
            or â€˜jsonâ€™).  If None (default), will try to determine
            which format based on if the first character of model is
            â€˜<â€™ or â€˜{â€˜.

      :Raises:
         **ValueError** â€“ If format is None and unable to identify
         XML/JON content, or if     format is not equal to â€˜xmlâ€™ or
         â€˜jsonâ€™.

   **path(key, yes={}, no={})**

      Return the path list of a subelement at any level uniquely
      identified by the specified conditions. Issues an error if
      either no match, or multiple matches are found.

      :Parameters:
         * **key** (*str*) â€“ Dictionary key to search for.

         * **yes** (*dict*) â€“ Key-value terms which the subelement
            must have to be considered a match.

         * **no** (*dict*) â€“ Key-value terms which the subelement
            must not have to be considered a match.

      :Returns:
         The subelement path list to the uniquely identified
         subelement.

      :Return type:
         list of str

      :Raises:
         **ValueError** â€“ If exactly one matching subelement is not
         identified.

   **paths(key, yes={}, no={})**

      Return a list of all path lists of all elements at any level
      identified by the specified conditions.

      :Parameters:
         * **key** (*str*) â€“ Dictionary key to search for.

         * **yes** (*dict*) â€“ Key-value terms which the subelement
            must have to be considered a match.

         * **no** (*dict*) â€“ Key-value terms which the subelement
            must not have to be considered a match.

      :Returns:
         The path lists for any matching subelements.

      :Return type:
         list

   **xml(fp=None, indent=None, kwargs)**

      Return the DataModelDict as XML content.

      :Parameters:
         * **fp** (*file-like object or None, optional*) â€“ An
            open file to write the content to.  If None (default),
            then the content is returned as a str.

         * **indent** (*int, str or None, optional*) â€“ If
            int, number of spaces to indent lines.  If str, will use
            that as the indentation. If None (default), the content
            will be inline.

         * ****kwargs** (*any*) â€“ Other keywords supported by
            xmltodict.unparse, except for output which is replaced by
            fp, and preprocessor, which is controlled.

      :Returns:
         The XML content (only returned if fp is None).

      :Return type:
         str, optional

**DataModelDict.joinpath(path: list, delimiter: str = '.',
openbracket: str = '[', closebracket: str = ']') -> str**

   Takes a path as a list and transforms it into a string.

   :Parameters:
      * **path** (*list*) â€“ The path list to join.

      * **delimiter** (*str*) â€“ The delimiter between subsequent
         element names.

      * **openbracket** (*str*) â€“ The opening indicator of list
         indices.

      * **closebracket** (*str*) â€“ The closing indicator of list
         indices.

   :Return type:
      The path as a delimited string.

**DataModelDict.parsepath(pathstr: str, delimiter: str = '.',
openbracket: str = '[', closebracket: str = ']') -> list**

   Takes a path as a string and parses it into a list of terms.

   :Parameters:
      * **pathstr** (*str*) â€“ The path string to parse.

      * **delimiter** (*str*) â€“ The delimiter between subsequent
         element names.

      * **openbracket** (*str*) â€“ The opening indicator of list
         indices.

      * **closebracket** (*str*) â€“ The closing indicator of list
         indices.

   :Returns:
      The path as a list.

   :Return type:
      list

**DataModelDict.uber_open_rmode(data: Union[str, bytes, pathlib.Path,
io.IOBase]) -> io.IOBase**

   Provides a uniform means of reading data from files, file-like
   objects, and string/bytes content.

   :Parameters:
      **data** (*file-like object, file path, or str/bytes
      file content*) â€“ The data that will be opened for reading.

   :Returns:
      An open file-like object that is in a bytes read mode.  If a
      file-like object is given, it is passed through after checking
      that it is for bytes content.  If a file path is given, the file
      is opened in â€˜rbâ€™ mode.  If bytes or string content is given,
      the content is returned in a BytesIO object.

   :Return type:
      file-like object

   :Raises:
      * **ValueError** â€“ If a file-like object in text mode is given.

      * **TypeError** â€“ If data is not a file-like object, bytes, str
         or Path.

      * **FileNotFoundError** â€“ If data is a pathlib.Path object and
         is not an existing file.