handling python errors

[Patrick C]

hey everyone,

i'm working with a list that would be something like
xx = ['0.53', 'n/a', '0.36', '0.45', '0.60']

and i want to do some calcuations with each item, lets say subtract one item from the item prior...not bad say something like...

results = []
while second < len(xx):
    first = 0
    second = 1
    results.append(xx[second] - xx[first])
    first += 1
    secodn += 1

that wouldnt be too bad... if it weren't for the n/a. And its important to keep that n/a in there.

what i'd like is, if the code is soppose to do soemthing like n/a - 0.53 for it to return "BadMath".. .

But when i use the code above i get the following error...

Traceback (most recent call last):
  File "<interactive input>", line 4, in <module>
ValueError: invalid literal for float(): n/a

Any ideas how i could get around that? Thanks

PC

[ilikepython]

hey everyone,

i'm working with a list that would be something like
xx = ['0.53', 'n/a', '0.36', '0.45', '0.60']

and i want to do some calcuations with each item, lets say subtract one item from the item prior...not bad say something like...

results = []
while second < len(xx):
    first = 0
    second = 1
    results.append(xx[second] - xx[first])
    first += 1
    secodn += 1

that wouldnt be too bad... if it weren't for the n/a. And its important to keep that n/a in there.

what i'd like is, if the code is soppose to do soemthing like n/a - 0.53 for it to return "BadMath".. .

But when i use the code above i get the following error...

Traceback (most recent call last):
  File "<interactive input>", line 4, in <module>
ValueError: invalid literal for float(): n/a

Any ideas how i could get around that? Thanks

PC

You can use a try and except block:
[code=python]
try:
# code that might raise an exception here
except ValueError:
# code the runs if the specified exception is raised

# program resumes
[/code]
Also, you while loop seems wrong.

[Patrick C]

Thanks for your suggestion on the try/except method. I tried to implement it into my fixed (hopefully) while loop. But I'm having problems.

I put 2 try/except loops in it because at different stages I'd get different errors.
What I was hoping to end up with was
sub = -.17, error(of some type), error(of some type), .15

I say error(of some type) because i'm not sure which error it would yield.

here's what I have

>>> stuff2 = ['0.53', '0.36', 'n/a', '0.45', '0.60']
>>> bb = 1
>>> aa = 0
>>> sub = []
>>> sub
[]
>>> while bb < len(stuff2):
... 	try:
... 		sub.append(stuff2[bb] - stuff2[aa])
... 		bb += 1
... 		aa += 1
... 		try:
... 			sub.append(stuff2[bb] - stuff2[aa])
... 			bb += 1
... 			aa += 1
... 		except ValueError:
... 			sub.append("error1")		
... 			bb += 1
... 			aa += 1
... 	except TypeError:		
... 		sub.append("error2")
... 		bb += 1
... 		aa += 1
... 
>>> sub
['error2', 'error2', 'error2', 'error2']

[Patrick C]

Ignore that, i forgot that stuff2 is still a string, if i still am having a problem, i'll put another post up.

thanks