emitjson 0.0.4

Help composing objects to build JSON.

Help composing objects to emit JSON.

emitjson.repository() creates a repository of functions to convert various type of objects to JSON-friendly objects. The repository is a single-dispatch generic function that returns a converted object if the converter for the type is registered.

The repository contains some default converters for types that are not supported by json module such as set() or datetime.datetime(). Also, default repository returns (shallow) copies of standard container types such as collections.abc.Mapping or collection.abc.Sequence. Items in the container object are also converted recursively.

>>> import datetime
>>> import emitjson
>>> my_repo = emitjson.repository()  # create emitjson repository
>>> src = [1, 2, datetime.datetime.now(), {4, 5, 6}]
>>> new = my_repo(src)
>>> print(new)
(1, 2, '2016-04-20T22:09:18.731157', (4, 5, 6))

You can add your own converters as singledispatch function. Following example add a converter to generate Base64 strings from bytes objects.

>>> import emitjson
>>> import base64
>>> my_repo = emitjson.repository()  # create emitjson repository
>>> @my_repo.register(bytes)
>>> def conv_bytes(obj):
...    # encode bytes object in Base64 format
...    return base64.b64encode(obj).decode('ascii')
...
>>> print(my_repo([b'abcd']))
('YWJjZA==', )

You can also define mapper class to convert objects to dictionary.

from emitjson repository, attr, ObjConverter

class Class1:
    def __init__(self):
        self.prop1 = 'spam'
        self.prop2 = 'ham'

class Class2:
    def __init__(self):
        self.prop3 = [Class1()]


my_repo = emitjson.repository()  # create emitjson repository

@my_repo.register(Class1)
class Class1Converter(ObjConverter):
    prop1 = attr    # get obj.prop1
    prop2 = attr    # get obj.prop2

@my_repo.register(Class2)
class Class2Converter(ObjConverter):
    prop_x = attr('prop3')  # get obj.prop3 but store as 'prop_x'

Requirements

• Python 3.4 or later

Functions

@repository()

Create a repository of object converters. The repository is an instance of the single-dispatch generic function.

The repository overrides following types by default.

• collections.abc.Sequence objects are converted to tuple. Elements in the sequence are converted recursively.

• Keys and values of the collections.abc.Mapping are converted recursively.

• datetime.date and datetime.datetime objects are converted to isoformat() string.

ObjConverter class

ObjConverter class create a converter from an arbitrary object to a dictionary. Values obtained from objects are also converted recursively.

Attribute names to be converted are defined as attr class members of ObjConverter class.

If an attribute of the ObjConverter is an instance of attr, attrname arguments specifies attribute name to be converted.

Resulting dict objects are also converted recursively.

ObjConverter.on_convert(obj, values)

on_convert method is called to obtain attribute of obj and store the value to the values dictionary. You can override on_convert() method to customize conversion.

class Class3:
    prop = 1

@myrepo.register(Class3)
class Class3Converter(ObjConverter):
    def on_convert(self, obj, values):
        super().on_convert(obj, values)
        values['dynamic_prop'] = obj.prop

print(myrepo(Class3())  # prints {'dynamic_prop': 1}

attr(attrname=None, map=None) class

Converts an attribute of object.

attrname overrides the attribute name if not omitted.

map argument which is a functon to convert a target object to arbitrary objects.

SAModelConverter class

SAModelConverter class create a converter from an SQLAlchemy model. Columns of the model are converted unless specified in IGNORES member of the class.

class Test(Base):
    __tablename__ = 'test'
    a = Column(Integer, primary_key=True)
    b = Column(Integer)
    c = Column(Integer)
    d = Column(Integer)

@myrepo.register(Test)
class TestModelConverter(SAModelConverter):
    IGNORES = ('c', 'd')    # ommit Test.c and Test.d

repository.fromSQLAlchemyModel(model, attrs=None, ignores=None)

Another way to register a converter of SQLAlchemy model. Columns of the model are converted unless the name of column is listed in ignore argument. attrs is a dictionary of key name and attr object.

# Converts Test model
myrepo.fromSQLAlchemyModel(Test,
    attrs={
        'fld1': attr,           # Emits Test.fld1 as value of 'fld1'
        'X_VALUE':attr('fld_X') # Emits Test.fld_X as value of 'X_VALUE'
    },
    ignores=('fld3', 'fld4')) # ignore Test.fld3 and Test.fld2

Copyright

Copyright (c) 2016 Atsuo Ishimoto

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.