Lee C -
Here is a technique for avoiding the if-elseif-elseif...-else method
for building objects. It is a modified form of ChainOfResponsibility
pattern, in which you have a collection of factory methods that all
have a common signature, or a collection of Factory classes that all
implement a "makeObject" method. These common methods probably take a
string, and return a generic object. Fortunately, such type
flexibility is *very* easy in Python. :)
Example:
I want to convert individual strings to native data types. I want to
detect integers, reals, complex numbers, and booleans (indicated by
'True' or 'False'). This is kind of similar to a parsing problem, but
it could also be used for deserializing or unpickling data of an
unknown original type.
Note the special treatment I have to go through with boolean values - I
needed to write a special makeBool routine, since Python will take any
non-empty string to be True, when what I want is 'True' to yield true
and 'False' to yield false.
Hope this gives you some alternative ideas to your cascading if's.
-- Paul
def makeBool(s):
if s in ('True','False'):
return s == 'True'
raise ValueError
converters = [ int, float, complex, makeBool, str ]
def makeObject(stringVar):
for conv in converters:
try:
val = conv(stringVar)
except Exception:
continue
else:
break;
return val
def test(s):
val = makeObject(s)
print s, val, type(val)
test('1')
test('1.0')
test('1+2j')
test('1+0j')
test('True')
test('False')
test('A')
prints:
1 1 <type 'int'>
1.0 1.0 <type 'float'>
1+2j (1+2j) <type 'complex'>
1+0j (1+0j) <type 'complex'>
True True <type 'bool'>
False False <type 'bool'>
A A <type 'str'>
--
http://mail.python.org/mailman/listinfo/python-list
