I've never found any need for an is_defined function. If in doubt I just
make sure and initialise all variables to a suitable value before use.
However, I'll assume you have a good use case.
I admit that that is the better practice. George's example was the
conversion of data from one form to another where the data is mixed
with complete and incomplete items. And Kay is looking at tuple
unpacking.
It's hard to beat try/except for these situations though.
I cleaned it up some more and figured out the proper use of
_getframe(). So no lambdas, and no passing of locals needed., and it
checks for globals and builtins before defining the default value so
as not to over write a readable value.
I'm not sure what the best behavior should be. Maybe a routine to
tell where a name is, ie.. local, global, builtin, or a writable
global? maybe isa() return the location or None.? I think that would
be better.
The best purpose for utilities like these is for debugging and getting
feedback about the environment. So I'm thinking of putting them in a
module for that purpose. I have a subroutine to list all the names
attached to an object. I think I can add that a bit now too.
#---Here's the code---------------------
import sys
def isa(v):
"""
Check if a varable exists in the current
(parent to this function), global, or
builtin name spaces.
use: bool = isa( str )
returns True or False
"""
plocals = sys._getframe(1).f_locals
if plocals.has_key(v) or globals().has_key(v) or \
__builtins__.locals().has_key(v):
return True
return False
def ifno(v, obj=None):
"""
Check if a varable does not exists, return a
default value, otherwise return the varable obj.
use: obj = ifno( str [,obj=None] )
if str exist, returns str's object
if str does not exist, returns specified object
"""
plocals = sys._getframe(1).f_locals
if plocals.has_key(v):
return plocals[v]
if globals().has_key(v):
return globals()[v]
if __builtins__.locals().has_key(v):
return __builtins__.locals()[v]
return obj
def test():
"""
Test isa() and ifno() functions:
"""
# Totally useless routine.
import random
for n in range(25):
# Delete a random x,y,z coordinate to
# simulate an unrealiabe data source.
d = random.choice([1,2,3])
if d==1:
if isa('x'): del x
elif d==2:
if isa('y'): del y
else:
if isa('z'): del z
# Replace the missing Varible with a random number.
r = int(random.random()*100)
x, y, z = ifno('x',r), ifno('y',r), ifno('z',r)
print x, y, z
if __name__ == '__main__':
test()
#-------------------------------------
