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Python library for BespON

Project description

The bespon package for Python encodes and decodes data in the BespON format.

Basic usage

Data is loaded in a manner analogous to Python’s json module:

  • bespon.load(<file-like object>)
  • bespon.loads(<string or bytes>)

Similarly, dumping data to a file or string:

  • bespon.dump(<obj>, <file-like object>)
  • bespon.dumps(<obj>)

At the moment, only dumping in indentation-style syntax is possible. Support for other styles is under development. Only dicts, lists, Unicode strings, byte strings, floats, ints, bools, and None are currently supported for dumping. Loading supports additional data types.

Lossless round-trip support

There is also support for lossless round-tripping. Data can be loaded, values can be modified, and then data can be saved again with minimal impact on the data file layout.

Data can be loaded from a file or string into an instance of the RoundtripAst class.

  • bespon.load_roundtrip_ast(<file-like object>)
  • bespon.loads_roundtrip_ast(<string or bytes>)

This class has two methods that allow data to be modified.

  • replace_val(<path>, <obj>) This replaces the object currently located at <path> within the data with <obj>. <path> must be a list or tuple consisting of dict keys and list indices. <obj> must currently be a Unicode string, float, int, or bool, and must have the same type as the object it is replacing.
  • replace_key(<path>, <obj>) This replaces the dict key at the end of <path> with the new key <obj> (which will map to the same value as the replaced key). <obj> must be a Unicode string, int, or bool, and must have the same type as the object it is replacing.

After data in a RoundtripAst instance has been modified, it may be encoded back into a string with the dumps() method. An example is shown below.

>>> ast = bespon.loads_roundtrip_ast("""
key.subkey.first = 123   # Comment
key.subkey.second = 0b1101
key.subkey.third = `literal \string`
>>> ast.replace_key(['key', 'subkey'], 'sk')
>>> ast.replace_val(['key', 'sk', 'second'], 7)
>>> ast.replace_val(['key', 'sk', 'third'], '\\another \\literal')
>>> ast.replace_key(['key', 'sk', 'third'], 'fourth')
>>> print(ast.dumps()) = 123   # Comment = 0b111 = `\another \literal`

This example illustrates several of BespON’s round-trip capabilities.

  • Comments and layout are preserved exactly.
  • Key renaming works with key paths. Every time a key appears in key paths, it is renamed.
  • When a number is modified, the new value is expressed in the same base as the old value.
  • When a quoted string is modified, the new value is quoted in the same style as the old value (at least to the extent that this is practical).
  • As soon as a key is modified, the new key must be used for further modifications. The old key is invalid.

Currently, round-trip support is limited to changing the value of any Unicode string, float, int, or bool, without changing the type. Support for changing data types and for more general data manipulation will be added in the future.

Advanced loading and dumping

The loading and dumping functions support several keyword arguments to customize data handling.


  • aliases (boolean, default True): Allow aliases.
  • circular_references (boolean, default False): Allow aliases to create circular references.
  • custom_parsers (dict, default None): Replace the default parser for a specified type with a custom parser. For example, using custom_parsers={'int': float} would cause all integers to be parsed with the float() function.
  • extended_types (boolean, default False): Enable preliminary support for set and odict tagged collections (for example, (set)> [1, 2, 3]). Enable preliminary support for complex number literals and rational number literals. Complex numbers currently use the general form 1.0+2.0i, where the real part is optional, the imaginary unit is represented with i, and numbers must be floats (either in decimal or hex form). Rational numbers use the form 1/2, where the numerator and denominator must both be decimal integers, and any sign must come before the fraction.
  • float_overflow_to_inf (boolean, default False): Whether non-inf floats are permitted to overflow into inf without raising an error.
  • integers (boolean, default True): Whether integers are permitted. Otherwise they are interpreted as floats.
  • only_ascii_unquoted (boolean, default True): Whether non-ASCII identifier-style strings are allowed unquoted.
  • only_ascii_source (boolean, default False): Whether non-ASCII code points are allowed to appear literally in the source (without being represented via backslash-escapes).
  • python_types (boolean, default False): Enable preliminary support for Python-specific data types. Currently this only supports tuple.
  • max_nesting_depth (int, default 100): Maximum permitted nesting depth for collections.


  • hex_floats (boolean, default False): Whether floats are dumped in hex form.
  • max_nesting_depth (int, default 100): Maximum permitted nesting depth of collections.

Spec conformance

The bespon package passes the BespON test suite.

Project details

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