path: root/README.rst

===============================================================================
parse_type
===============================================================================

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`parse_type`_ extends the `parse`_ module (opposite of `string.format()`_)
with the following features:

* build type converters for common use cases (enum/mapping, choice)
* build a type converter with a cardinality constraint (0..1, 0..*, 1..*)
    from the type converter with cardinality=1.
* compose a type converter from other type converters
* an extended parser that supports the CardinalityField naming schema
    and creates missing type variants (0..1, 0..*, 1..*) from the
    primary type converter

.. _parse_type: http://pypi.python.org/pypi/parse_type
.. _parse:      http://pypi.python.org/pypi/parse
.. _`string.format()`: http://docs.python.org/library/string.html#format-string-syntax


Definitions
-------------------------------------------------------------------------------

*type converter*
    A type converter function that converts a textual representation
    of a value type into instance of this value type.
    In addition, a type converter function is often annotated with attributes
    that allows the `parse`_ module to use it in a generic way.
    A type converter is also called a *parse_type* (a definition used here).

*cardinality field*
    A naming convention for related types that differ in cardinality.
    A cardinality field is a type name suffix in the format of a field.
    It allows parse format expression, ala::

        "{person:Person}"     #< Cardinality: 1    (one; the normal case)
        "{person:Person?}"    #< Cardinality: 0..1 (zero or one  = optional)
        "{persons:Person*}"   #< Cardinality: 0..* (zero or more = many0)
        "{persons:Person+}"   #< Cardinality: 1..* (one  or more = many)

    This naming convention mimics the relationship descriptions in UML diagrams.


Basic Example
-------------------------------------------------------------------------------

Define an own type converter for numbers (integers):

.. code-block:: python

    # -- USE CASE:
    def parse_number(text):
        return int(text)
    parse_number.pattern = r"\d+"  # -- REGULAR EXPRESSION pattern for type.

This is equivalent to:

.. code-block:: python

    import parse

    @parse.with_pattern(r"\d+")
    def parse_number(text):
         return int(text)
    assert hasattr(parse_number, "pattern")
    assert parse_number.pattern == r"\d+"


.. code-block:: python

    # -- USE CASE: Use the type converter with the parse module.
    schema = "Hello {number:Number}"
    parser = parse.Parser(schema, dict(Number=parse_number))
    result = parser.parse("Hello 42")
    assert result is not None, "REQUIRE: text matches the schema."
    assert result["number"] == 42

    result = parser.parse("Hello XXX")
    assert result is None, "MISMATCH: text does not match the schema."

.. hint::

    The described functionality above is standard functionality
    of the `parse`_ module. It serves as introduction for the remaining cases.


Cardinality
-------------------------------------------------------------------------------

Create an type converter for "ManyNumbers" (List, separated with commas)
with cardinality "1..* = 1+" (many) from the type converter for a "Number".

.. code-block:: python

    # -- USE CASE: Create new type converter with a cardinality constraint.
    # CARDINALITY: many := one or more (1..*)
    from parse import Parser
    from parse_type import TypeBuilder
    parse_numbers = TypeBuilder.with_many(parse_number, listsep=",")

    schema = "List: {numbers:ManyNumbers}"
    parser = Parser(schema, dict(ManyNumbers=parse_numbers))
    result = parser.parse("List: 1, 2, 3")
    assert result["numbers"] == [1, 2, 3]


Create an type converter for an "OptionalNumbers" with cardinality "0..1 = ?"
(optional) from the type converter for a "Number".

.. code-block:: python

    # -- USE CASE: Create new type converter with cardinality constraint.
    # CARDINALITY: optional := zero or one (0..1)
    from parse import Parser
    from parse_type import TypeBuilder

    parse_optional_number = TypeBuilder.with_optional(parse_number)
    schema = "Optional: {number:OptionalNumber}"
    parser = Parser(schema, dict(OptionalNumber=parse_optional_number))
    result = parser.parse("Optional: 42")
    assert result["number"] == 42
    result = parser.parse("Optional: ")
    assert result["number"] == None


Enumeration (Name-to-Value Mapping)
-------------------------------------------------------------------------------

Create an type converter for an "Enumeration" from the description of
the mapping as dictionary.

.. code-block:: python

    # -- USE CASE: Create a type converter for an enumeration.
    from parse import Parser
    from parse_type import TypeBuilder

    parse_enum_yesno = TypeBuilder.make_enum({"yes": True, "no": False})
    parser = Parser("Answer: {answer:YesNo}", dict(YesNo=parse_enum_yesno))
    result = parser.parse("Answer: yes")
    assert result["answer"] == True


Create an type converter for an "Enumeration" from the description of
the mapping as an enumeration class (`Python 3.4 enum`_ or the `enum34`_
backport; see also: `PEP-0435`_).

.. code-block:: python

    # -- USE CASE: Create a type converter for enum34 enumeration class.
    # NOTE: Use Python 3.4 or enum34 backport.
    from parse import Parser
    from parse_type import TypeBuilder
    from enum import Enum

    class Color(Enum):
        red   = 1
        green = 2
        blue  = 3

    parse_enum_color = TypeBuilder.make_enum(Color)
    parser = Parser("Select: {color:Color}", dict(Color=parse_enum_color))
    result = parser.parse("Select: red")
    assert result["color"] is Color.red

.. _`Python 3.4 enum`: http://docs.python.org/3.4/library/enum.html#module-enum
.. _enum34:   http://pypi.python.org/pypi/enum34
.. _PEP-0435: http://www.python.org/dev/peps/pep-0435


Choice (Name Enumeration)
-------------------------------------------------------------------------------

A Choice data type allows to select one of several strings.

Create an type converter for an "Choice" list, a list of unique names
(as string).

.. code-block:: python

    from parse import Parser
    from parse_type import TypeBuilder

    parse_choice_yesno = TypeBuilder.make_choice(["yes", "no"])
    schema = "Answer: {answer:ChoiceYesNo}"
    parser = Parser(schema, dict(ChoiceYesNo=parse_choice_yesno))
    result = parser.parse("Answer: yes")
    assert result["answer"] == "yes"


Variant (Type Alternatives)
-------------------------------------------------------------------------------

Sometimes you need a type converter that can accept text for multiple
type converter alternatives. This is normally called a "variant" (or: union).

Create an type converter for an "Variant" type that accepts:

* Numbers (positive numbers, as integer)
* Color enum values (by name)

.. code-block:: python

    from parse import Parser, with_pattern
    from parse_type import TypeBuilder
    from enum import Enum

    class Color(Enum):
        red   = 1
        green = 2
        blue  = 3

    @with_pattern(r"\d+")
    def parse_number(text):
        return int(text)

    # -- MAKE VARIANT: Alternatives of different type converters.
    parse_color = TypeBuilder.make_enum(Color)
    parse_variant = TypeBuilder.make_variant([parse_number, parse_color])
    schema = "Variant: {variant:Number_or_Color}"
    parser = Parser(schema, dict(Number_or_Color=parse_variant))

    # -- TEST VARIANT: With number, color and mismatch.
    result = parser.parse("Variant: 42")
    assert result["variant"] == 42
    result = parser.parse("Variant: blue")
    assert result["variant"] is Color.blue
    result = parser.parse("Variant: __MISMATCH__")
    assert not result



Extended Parser with CardinalityField support
-------------------------------------------------------------------------------

The parser extends the ``parse.Parser`` and adds the following functionality:

* supports the CardinalityField naming scheme
* automatically creates missing type variants for types with
  a CardinalityField by using the primary type converter for cardinality=1
* extends the provide type converter dictionary with new type variants.

Example:

.. code-block:: python

    # -- USE CASE: Parser with CardinalityField support.
    # NOTE: Automatically adds missing type variants with CardinalityField part.
    # USE:  parse_number() type converter from above.
    from parse_type.cfparse import Parser

    # -- PREPARE: parser, adds missing type variant for cardinality 1..* (many)
    type_dict = dict(Number=parse_number)
    schema = "List: {numbers:Number+}"
    parser = Parser(schema, type_dict)
    assert "Number+" in type_dict, "Created missing type variant based on: Number"

    # -- USE: parser.
    result = parser.parse("List: 1, 2, 3")
    assert result["numbers"] == [1, 2, 3]