Human-readable text syntax

The preserves.text module implements the Preserves human-readable text syntax.

The main entry points are functions stringify, parse, and parse_with_annotations.

>>> stringify(Record(Symbol('hi'), [1, [2, 3]]))
'<hi 1 [2 3]>'
>>> parse('<hi 1 [2 3]>')
#hi(1, (2, 3))

Formatter(format_embedded=lambda x: x, indent=None, with_commas=False, trailing_comma=False, include_annotations=True)

Bases: TextCodec

Printer (and indenting pretty-printer) for producing human-readable syntax from Preserves Values.

>>> f = Formatter()
>>> f.append({'a': 1, 'b': 2})
>>> f.append(Record(Symbol('label'), ['field1', ['field2item1', 'field2item2']]))
>>> print(f.contents())
{"a": 1 "b": 2} <label "field1" ["field2item1" "field2item2"]>

>>> f = Formatter(indent=4)
>>> f.append({'a': 1, 'b': 2})
>>> f.append(Record(Symbol('label'), ['field1', ['field2item1', 'field2item2']]))
>>> print(f.contents())
{
    "a": 1
    "b": 2
}
<label "field1" [
    "field2item1"
    "field2item2"
]>

Parameters:

Name	Type	Description	Default
format_embedded		function accepting an Embedded.embeddedValue and returning a Value for serialization.	lambda x: x
indent	int | None	None disables indented pretty-printing; otherwise, an int specifies indentation per nesting-level.	None
with_commas	bool	True causes commas to separate sequence and set items and dictionary entries; False omits commas.	False
trailing_comma	bool	True causes a comma to be printed after the final item or entry in a sequence, set or dictionary; False omits this trailing comma	False
include_annotations	bool	True causes annotations to be included in the output; False causes them to be omitted.	True

Attributes:

Name	Type	Description
indent_delta	int	indentation per nesting-level
chunks	list[str]	fragments of output

Source code in preserves/text.py

def __init__(self,
             format_embedded=lambda x: x,
             indent=None,
             with_commas=False,
             trailing_comma=False,
             include_annotations=True):
    super(Formatter, self).__init__()
    self.indent_delta = 0 if indent is None else indent
    self.indent_distance = 0
    self.nesting = 0
    self.with_commas = with_commas
    self.trailing_comma = trailing_comma
    self.chunks = []
    self._format_embedded = format_embedded
    self.include_annotations = include_annotations

append(v)

Extend self.chunks with at least one chunk, together making up the text representation of v.

Source code in preserves/text.py

def append(self, v):
    """Extend `self.chunks` with at least one chunk, together making up the text
    representation of `v`."""
    if self.chunks and self.nesting == 0:
        self.write_indent_space()
    try:
        self.nesting += 1
        self._append(v)
    finally:
        self.nesting -= 1

contents()

Returns a str constructed from the join of the chunks in self.chunks.

Source code in preserves/text.py

def contents(self):
    """Returns a `str` constructed from the join of the chunks in `self.chunks`."""
    return u''.join(self.chunks)

is_indenting()

Returns True iff this Formatter is in pretty-printing indenting mode.

Source code in preserves/text.py

def is_indenting(self):
    """Returns `True` iff this [Formatter][preserves.text.Formatter] is in pretty-printing
    indenting mode."""
    return self.indent_delta > 0

Parser(input_buffer='', include_annotations=False, parse_embedded=lambda x: x)

Bases: TextCodec

Parser for the human-readable Preserves text syntax.

Parameters:

Name	Type	Description	Default
input_buffer	str	initial contents of the input buffer; may subsequently be extended by calling extend.	''
include_annotations	bool	if True, wrap each value and subvalue in an Annotated object.	False
parse_embedded		function accepting a Value and returning a possibly-decoded form of that value suitable for placing into an Embedded object.	lambda x: x

Normal usage is to supply input text, and keep calling next until a ShortPacket exception is raised:

>>> d = Parser('123 "hello" @x []')
>>> d.next()
123
>>> d.next()
'hello'
>>> d.next()
()
>>> d.next()
Traceback (most recent call last):
  ...
preserves.error.ShortPacket: Short input buffer

Alternatively, keep calling try_next until it yields None, which is not in the domain of Preserves Values:

>>> d = Parser('123 "hello" @x []')
>>> d.try_next()
123
>>> d.try_next()
'hello'
>>> d.try_next()
()
>>> d.try_next()

For convenience, Parser implements the iterator interface, backing it with try_next, so you can simply iterate over all complete values in an input:

>>> d = Parser('123 "hello" @x []')
>>> list(d)
[123, 'hello', ()]

>>> for v in Parser('123 "hello" @x []'):
...     print(repr(v))
123
'hello'
()

Supply include_annotations=True to read annotations alongside the annotated values:

>>> d = Parser('123 "hello" @x []', include_annotations=True)
>>> list(d)
[123, 'hello', @#x ()]

If you are incrementally reading from, say, a socket, you can use extend to add new input as if comes available:

>>> d = Parser('123 "he')
>>> d.try_next()
123
>>> d.try_next() # returns None because the input is incomplete
>>> d.extend('llo"')
>>> d.try_next()
'hello'
>>> d.try_next()

Attributes:

Name	Type	Description
input_buffer	str	buffered input waiting to be processed
index	int	read position within input_buffer

Source code in preserves/text.py

def __init__(self, input_buffer=u'', include_annotations=False, parse_embedded=lambda x: x):
    super(Parser, self).__init__()
    self.input_buffer = input_buffer
    self.index = 0
    self.include_annotations = include_annotations
    self.parse_embedded = parse_embedded

extend(text)

Appends text to the remaining contents of self.input_buffer, trimming already-processed text from the front of self.input_buffer and resetting self.index to zero.

Source code in preserves/text.py

def extend(self, text):
    """Appends `text` to the remaining contents of `self.input_buffer`, trimming already-processed
    text from the front of `self.input_buffer` and resetting `self.index` to zero."""
    self.input_buffer = self.input_buffer[self.index:] + text
    self.index = 0

next()

Reads the next complete Value from the internal buffer, raising ShortPacket if too few bytes are available, or DecodeError if the input is invalid somehow.

Source code in preserves/text.py

def next(self):
    """Reads the next complete `Value` from the internal buffer, raising
    [ShortPacket][preserves.error.ShortPacket] if too few bytes are available, or
    [DecodeError][preserves.error.DecodeError] if the input is invalid somehow.

    """
    self.skip_whitespace()
    c = self.peek()
    if c == '"':
        self.skip()
        return self.wrap(self.read_string('"'))
    if c == '|':
        self.skip()
        return self.wrap(Symbol(self.read_string('|')))
    if c == '@':
        self.skip()
        return self.unshift_annotation(self.next(), self.next())
    if c == ';':
        raise DecodeError('Semicolon is reserved syntax')
    if c == ':':
        raise DecodeError('Unexpected key/value separator between items')
    if c == '#':
        self.skip()
        c = self.nextchar()
        if c in ' \t': return self.unshift_annotation(self.comment_line(), self.next())
        if c in '\n\r': return self.unshift_annotation('', self.next())
        if c == '!':
            return self.unshift_annotation(
                Record(Symbol('interpreter'), [self.comment_line()]),
                self.next())
        if c == 'f': self.require_delimiter('#f'); return self.wrap(False)
        if c == 't': self.require_delimiter('#t'); return self.wrap(True)
        if c == '{': return self.wrap(self.read_set())
        if c == '"': return self.wrap(self.read_literal_binary())
        if c == 'x':
            c = self.nextchar()
            if c == '"': return self.wrap(self.read_hex_binary())
            if c == 'd': return self.wrap(self.read_hex_float())
            raise DecodeError('Invalid #x syntax')
        if c == '[': return self.wrap(self.read_base64_binary())
        if c == ':':
            if self.parse_embedded is None:
                raise DecodeError('No parse_embedded function supplied')
            return self.wrap(Embedded(self.parse_embedded(self.next())))
        raise DecodeError('Invalid # syntax')
    if c == '<':
        self.skip()
        vs = self.upto('>', False)
        if len(vs) == 0:
            raise DecodeError('Missing record label')
        return self.wrap(Record(vs[0], vs[1:]))
    if c == '[':
        self.skip()
        return self.wrap(self.upto(']', True))
    if c == '{':
        self.skip()
        return self.wrap(self.read_dictionary())
    if c in '>]},':
        raise DecodeError('Unexpected ' + c)
    self.skip()
    return self.wrap(self.read_raw_symbol_or_number([c]))

try_next()

Like next, but returns None instead of raising ShortPacket.

Source code in preserves/text.py

def try_next(self):
    """Like [next][preserves.text.Parser.next], but returns `None` instead of raising
    [ShortPacket][preserves.error.ShortPacket]."""
    start = self.index
    try:
        return self.next()
    except ShortPacket:
        self.index = start
        return None

parse(text, **kwargs)

Yields the first complete encoded value from text, passing kwargs through to the Parser constructor. Raises exceptions as per next.

Parameters:

Name	Type	Description	Default
text	str	encoded data to decode	required

Source code in preserves/text.py

def parse(text, **kwargs):
    """Yields the first complete encoded value from `text`, passing `kwargs` through to the
    [Parser][preserves.text.Parser] constructor. Raises exceptions as per
    [next][preserves.text.Parser.next].

    Args:
        text (str): encoded data to decode

    """
    return Parser(input_buffer=text, **kwargs).next()

parse_with_annotations(bs, **kwargs)

Like parse, but supplying include_annotations=True to the Parser constructor.

Source code in preserves/text.py

def parse_with_annotations(bs, **kwargs):
    """Like [parse][preserves.text.parse], but supplying `include_annotations=True` to the
    [Parser][preserves.text.Parser] constructor."""
    return Parser(input_buffer=bs, include_annotations=True, **kwargs).next()

stringify(v, **kwargs)

Convert a single Value v to a string. Any supplied kwargs are passed on to the underlying Formatter constructor.

Source code in preserves/text.py

def stringify(v, **kwargs):
    """Convert a single `Value` `v` to a string. Any supplied `kwargs` are passed on to the
    underlying [Formatter][preserves.text.Formatter] constructor."""
    e = Formatter(**kwargs)
    e.append(v)
    return e.contents()