Re: Python Pseudo-Switch
# -*- python -*-
import sys
def switchFor (target):
sw = '__switch_table__'
# please pretend the frame hack is not here,
# it happens to work for classes and messing with
# frame stack in a try/except is probably okay
try:
raise Exception()
except:
defs = sys.exc_info()[2].tb_frame.f_back.f_locals
if sw not in defs:
defs[sw] = {}
table = defs[sw]
def _(meth):
table[target] = meth
return meth
return _
class SwitchMixin (object):
def __init__ (self):
self.__switch_table__ = self.__switch_table__.copy()
def switchOn (self, target, *args, **kw):
return self.__switch_table__[target](self, *args, **kw)
if __name__ == '__main__':
class SwitchTest(SwitchMixin):
@switchFor("foo")
def switch (self, arg):
print arg * 3
@switchFor("bar")
def switch (self, arg):
print "__%s__" % (arg,)
@switchFor("baz")
def switch (self, arg):
print arg + ''.join(reversed(arg))
st = SwitchTest()
st.switchOn("foo", "oof")
st.switchOn("bar", "rab")
st.switchOn("baz", "zab")
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Re: Python Pseudo-Switch
James Stroud wrote:
> Hello All,
>
> Because of my poorly designing a database, I have recently found it
necessary
> to explore the wonders of the Python pseudo-switch:
>
> do_case = { "A" : lambda x: x["bob"],
> "B" : lambda x: x["carol"],
> "C" : lambda x: "Ted",
> "D" : lambda x: do_something(x) }
>
class CaseThing:
def pref_A (self, x):
return x["bob"]
def pref_B (self, x):
return x["carol"]
def pref_C (self, x);
return "Ted"
def pref_D (self, x)
return do_something(x)
def getThing (self, x):
attr = getattr(self, 'pref_%s' % (x,))
if attr is not None:
return attr
else:
raise SomeError("Thing %s does not exist" % (x,))
my_thing = CaseThing().getThing(get_value_from_thin_air)(adict)
You can do something similar with method decorators for more complex
strings than what's allowed for python method names.
> my_thing = do_case[get_value_from_thin_air()](adict)
>
>
> How to handle this kind of thing when lambda is removed from the
language,
> beside the obvious def'ing those tiny little functions?
>
> James
>
> --
> James Stroud
> UCLA-DOE Institute for Genomics and Proteomics
> Box 951570
> Los Angeles, CA 90095
>
> http://www.jamesstroud.com/
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Re: Python Pseudo-Switch
James Stroud wrote:
> Hello All,
>
> Because of my poorly designing a database, I have recently found it
necessary
> to explore the wonders of the Python pseudo-switch:
>
> do_case = { "A" : lambda x: x["bob"],
> "B" : lambda x: x["carol"],
> "C" : lambda x: "Ted",
> "D" : lambda x: do_something(x) }
>
> my_thing = do_case[get_value_from_thin_air()](adict)
>
>
> How to handle this kind of thing when lambda is removed from the
language,
> beside the obvious def'ing those tiny little functions?
You can always re-invent lambda.
>>> def lambda2(arg_names, expression):
...exec 'def _(%s): return %s' % (','.join(arg_names), expression)
...return _
...
>>> add = lambda2(('x', 'y'), 'x + y')
>>> add(3, 4)
7
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Re: Python Pseudo-Switch
"James Stroud" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> Because of my poorly designing a database, I have recently found it
> necessary
> to explore the wonders of the Python pseudo-switch:
>
> do_case = { "A" : lambda x: x["bob"],
>"B" : lambda x: x["carol"],
>"C" : lambda x: "Ted",
>"D" : lambda x: do_something(x) }
>
> my_thing = do_case[get_value_from_thin_air()](adict)
>
> How to handle this kind of thing when lambda is removed from the
> language,
> beside the obvious def'ing those tiny little functions?
I don't believe any cast-in-concrete decision about lambda has been made
yet. I expect there will be a PEP for removals when appropriate. Comments
such as this will bolster the case against removal without replacement if
then resubmitted
TJR
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Python Pseudo-Switch
Hello All,
Because of my poorly designing a database, I have recently found it necessary
to explore the wonders of the Python pseudo-switch:
do_case = { "A" : lambda x: x["bob"],
"B" : lambda x: x["carol"],
"C" : lambda x: "Ted",
"D" : lambda x: do_something(x) }
my_thing = do_case[get_value_from_thin_air()](adict)
How to handle this kind of thing when lambda is removed from the language,
beside the obvious def'ing those tiny little functions?
James
--
James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095
http://www.jamesstroud.com/
--
http://mail.python.org/mailman/listinfo/python-list
