1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
|
===============================================================================
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]
|