metaparams 1.0.4

metaparams

metaparams is a MetaClass/Class/Decorator infrastructure to define params without invoking objects and have them automatically parse/remove the kwargs passed to the class in which they are intalled

Documentation

Read the full documentation at readthedocs.org:

• metaparams documentation

Python 2/3 Support

• Python 2.7

• Python 3.2/3.3/3.4/3.5

• It also works with pypy and pypy3

Installation

From pypi:

pip install metaparams

From source:

• Place the metaparams directory found in the sources inside your project

Features:

• metaparams decorator to params-enable any class

• ParamsBase a class from which to subclass to also be params-enabled

• MetaParams a MetaClass for more complex usage pattern

Quick Usage

The example below is available in the source as a single file test. It’s broken down into parts to ease up reading:

from __future__ import (absolute_import, division, print_function,
                        unicode_literals)


from metaparams import metaparams, MetaParams, ParamsBase

print('=' * 50)
print('Creating A with params with DECORATOR')


@metaparams
class A(object):

    params = (
        ('p1', True, 'doc'),
        ('p2', 99),
    )

    def __init__(self):
        pass

print('-- Instantiating A with no kwargs')
a = A()

# Defined params are reachable below the attribute params
print('a.params.p1:', a.params.p1)
print('a.params.p2:', a.params.p2)

# Modification of default values can be checked
print('Checking if p1 has default value:', a.params._isdefault('p1'))

print('=' * 50)
print('Creating B as subclass from A, changing p1, adding p3')

This first part produces the following output:

==================================================
Creating A with params with DECORATOR
-- Instantiating A with no kwargs
a.params.p1: True
a.params.p2: 99
Checking if p1 has default value: True

The 2nd part:

# Inheriting with modification an extension
class B(A):

    params = (
        ('p1', False,),  # changed default value of p1
        ('p3', None),  # new parameter
    )

    def __init__(self):
        pass

print('-- Instantiating B with no kwargs')
b = B()

# Defined params are reachable below the attribute params
print('b.param.p1 (default changed):', b.params.p1)
print('b.params.p2 (same default):', b.params.p2)
print('b.params.p3 (new param):', b.params.p3)

# Modification of default values can be checked
print('Checking if p1 has default value:', b.params._isdefault('p1'))

# Over the class we can also check defaults
# B has different default value for p1 than A
print('Checking default in B for p1 is not the same as default in A:',
      b.params.p1 != A.params._default('p1'))

Output:

==================================================
Creating B as subclass from A, changing p1, adding p3
-- Instantiating B with no kwargs
b.param.p1 (default changed): False
b.params.p2 (same default): 99
b.params.p3 (new param): None
Checking if p1 has default value: True
Checking default in B for p1 is not the same as default in A: True

3rd part:

print('=' * 50)
print('Recreating A with Decorator - name is "kargs" and short alias')


# The name of the attribute 'params' can be changed
# and a shorter alias (PEP-8 ...) added
@metaparams(_pname='kargs', _pshort=True)
class A(object):

    kargs = (
        ('p1', True, 'doc'),
        ('p2', 99),
    )

    def __init__(self):
        pass

print('-- Instantiating A with no kwargs')
a = A()

# Defined params are reachable below the attribute params
print('Checking if a params are reachable over "kargs"')
print('a.kargs.p1:', a.kargs.p1)
print('a.kargs.p2:', a.kargs.p2)

print('Checking if a params are reachable over shorter alias "k"')
print(a.k.p1)
print(a.k.p2)

# Modification of default values can be checked
print('Checking if p1 has default value:', a.kargs._isdefault('p1'))

Output:

==================================================
Recreating A with Decorator - name is "kargs" and short alias
-- Instantiating A with no kwargs
Checking if a params are reachable over "kargs"
a.kargs.p1: True
a.kargs.p2: 99
Checking if a params are reachable over shorter alias "k"
True
99
Checking if p1 has default value: True

4th part:

print('=' * 50)
print('Recreating A with new attr for params - "kargs" and short alias')
print('USING THE METACLASS')


# The metaclass works also so ... but it's a metaclass
class A(MetaParams.as_metaclass(_pname='kargs', _pshort=True)):

    kargs = (
        ('p1', True, 'doc'),
        ('p2', 99),
    )

    def __init__(self):
        pass

a = A()

# Defined params are reachable below the attribute params
print('Checking if a params are reachable over "kargs"')
print('a.kargs.p1:', a.kargs.p1)
print('a.kargs.p2:', a.kargs.p2)

print('Checking if a params are reachable over shorter alias "k"')
print(a.k.p1)
print(a.k.p2)

# Modification of default values can be checked
print('Checking if p1 has default value:', a.kargs._isdefault('p1'))

Output:

==================================================
Recreating A with new attr for params - "kargs" and short alias
USING THE METACLASS
Checking if a params are reachable over "kargs"
a.kargs.p1: True
a.kargs.p2: 99
Checking if a params are reachable over shorter alias "k"
True
99
Checking if p1 has default value: True

Final part:

print('=' * 50)
print('Recreating A with ParamsBase ... nothing can be changed')

# And finally an already cooked base class with no customization
class A(ParamsBase):

    params = (
        ('p1', True, 'doc'),
        ('p2', 99),
    )

    def __init__(self):
        pass

a = A()

# Defined params are reachable below the attribute params
print('a.params.p1:', a.params.p1)
print('a.params.p2:', a.params.p2)

# Modification of default values can be checked
print('Checking if p1 has default value:', a.params._isdefault('p1'))

Output:

==================================================
Recreating A with ParamsBase ... nothing can be changed
a.params.p1: True
a.params.p2: 99
Checking if p1 has default value: True