formations/algo/poo/cours/annexes/symbol.txt

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Symbols
=======
Using sets
-----------
There are different ways of defining symbols.
You can do it very simply with sets::
>>> s = set("abc", "def", "ghi")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: set expected at most 1 arguments, got 3
>>> s = set(["abc", "def", "ghi"])
>>> s
set(['abc', 'ghi', 'def'])
>>> "abc" in s
True
>>>
If you are using python 3.X, the notation::
Python 3.5.2 (default, Sep 10 2016, 08:21:44)
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> 1 in {1,2,3}
True
>>>
is very effective for working with symbols.
Use immutable sets.
Using namespaces
-----------------
Here is a real world example from the tiramisu library
.. code-block:: python
# ____________________________________________________________
class _NameSpace(object):
"""convenient class that emulates a module
and builds constants (that is, unique names)
when attribute is added, we cannot delete it
"""
def __setattr__(self, name, value):
if name in self.__dict__: # pragma: optional cover
raise ConstError(_("can't rebind {0}").format(name))
self.__dict__[name] = value
def __delattr__(self, name): # pragma: optional cover
if name in self.__dict__:
raise ConstError(_("can't unbind {0}").format(name))
raise ValueError(name)
class GroupModule(_NameSpace):
"emulates a module to manage unique group (OptionDescription) names"
class GroupType(str):
"""allowed normal group (OptionDescription) names
*normal* means : groups that are not master
"""
pass
class DefaultGroupType(GroupType):
"""groups that are default (typically 'default')"""
pass
class MasterGroupType(GroupType):
"""allowed normal group (OptionDescription) names
*master* means : groups that have the 'master' attribute set
"""
pass
class OwnerModule(_NameSpace):
"""emulates a module to manage unique owner names.
owners are living in `Config._cfgimpl_value_owners`
"""
class Owner(str):
"""allowed owner names
"""
pass
class DefaultOwner(Owner):
"""groups that are default (typically 'default')"""
pass
class MultiTypeModule(_NameSpace):
"namespace for the master/slaves"
class MultiType(str):
pass
class DefaultMultiType(MultiType):
pass
class MasterMultiType(MultiType):
pass
class SlaveMultiType(MultiType):
pass
# ____________________________________________________________
def populate_groups():
"""populates the available groups in the appropriate namespaces
groups.default
default group set when creating a new optiondescription
groups.master
master group is a special optiondescription, all suboptions should be
multi option and all values should have same length, to find master's
option, the optiondescription's name should be same than de master's
option
groups.family
example of group, no special behavior with this group's type
"""
groups.default = groups.DefaultGroupType('default')
groups.master = groups.MasterGroupType('master')
groups.family = groups.GroupType('family')
def populate_owners():
"""populates the available owners in the appropriate namespaces
default
is the config owner after init time
user
is the generic is the generic owner
"""
setattr(owners, 'default', owners.DefaultOwner('default'))
setattr(owners, 'user', owners.Owner('user'))
def addowner(name):
"""
:param name: the name of the new owner
"""
setattr(owners, name, owners.Owner(name))
setattr(owners, 'addowner', addowner)
# ____________________________________________________________
# populate groups and owners with default attributes
groups = GroupModule()
populate_groups()
owners = OwnerModule()
populate_owners()