=============================================================================== parse_type =============================================================================== .. image:: https://img.shields.io/travis/jenisys/parse_type/master.svg :target: https://travis-ci.org/jenisys/parse_type :alt: Travis CI Build Status .. image:: https://img.shields.io/pypi/v/parse_type.svg :target: https://pypi.python.org/pypi/parse_type :alt: Latest Version .. image:: https://img.shields.io/pypi/dm/parse_type.svg :target: https://pypi.python.org/pypi/parse_type :alt: Downloads .. image:: https://img.shields.io/pypi/l/parse_type.svg :target: https://pypi.python.org/pypi/parse_type/ :alt: License `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]