try/except within a while loop problem

[Patrick C]

Hey,

If i use a try/except clause to get around something like a TypeError, will that immediately bust me out of a while loop?

If so, is there any way i can tell it to stay in the while loop until its completed.

here's what I'm doing:

>>> stuff2
['0.53', '0.36', 'n/a', '0.45', '0.60']
>>> aa = 0
>>> bb = 1
>>> sub = []
>>> while bb < len(stuff2):
... 	try:
... 		sub.append(float(stuff2[bb]) - float(stuff2[aa]))
... 		bb += 1
... 		aa += 1
... 		try:
... 			sub.append(float(stuff2[bb]) - float(stuff2[aa]))
... 			bb += 1
... 			aa += 1
... 		except ValueError:
... 			sub.append("error1")		
... 			bb += 1
... 			aa += 1
... 	except TypeError:		
... 		sub.append("error2")
... 		bb += 1
... 		aa += 1
... 
Traceback (most recent call last):
  File "<interactive input>", line 3, in <module>
ValueError: invalid literal for float(): n/a
>>> sub
[-0.17000000000000004, 'error1']
>>>

thanks for all of your help

[bvdet]

Hey,

If i use a try/except clause to get around something like a TypeError, will that immediately bust me out of a while loop?

If so, is there any way i can tell it to stay in the while loop until its completed.

here's what I'm doing:

>>> stuff2
['0.53', '0.36', 'n/a', '0.45', '0.60']
>>> aa = 0
>>> bb = 1
>>> sub = []
>>> while bb < len(stuff2):
... 	try:
... 		sub.append(float(stuff2[bb]) - float(stuff2[aa]))
... 		bb += 1
... 		aa += 1
... 		try:
... 			sub.append(float(stuff2[bb]) - float(stuff2[aa]))
... 			bb += 1
... 			aa += 1
... 		except ValueError:
... 			sub.append("error1")		
... 			bb += 1
... 			aa += 1
... 	except TypeError:		
... 		sub.append("error2")
... 		bb += 1
... 		aa += 1
... 
Traceback (most recent call last):
  File "<interactive input>", line 3, in <module>
ValueError: invalid literal for float(): n/a
>>> sub
[-0.17000000000000004, 'error1']
>>>

thanks for all of your help

I am unsure about the result you are looking for. This code will pass on a ValueError (trying to convert 'n/a' to a float) and break out of the loop on an IndexError (trying to subtract an item that is beyond the length of the list):[code=Python]stuff2 = ['0.53', '0.36', 'n/a', '0.45', '0.60']
sub = []
for i, item in enumerate(stuff 2):
try:
sub.append(floa t(item) - float(stuff2[i+1]))
except ValueError:
pass
except IndexError:
break
print sub [/code]
Output:
>>> [0.1700000000000 0004, -0.1499999999999 9997]

[ilikepython]

Hey,

If i use a try/except clause to get around something like a TypeError, will that immediately bust me out of a while loop?

If so, is there any way i can tell it to stay in the while loop until its completed.

here's what I'm doing:

>>> stuff2
['0.53', '0.36', 'n/a', '0.45', '0.60']
>>> aa = 0
>>> bb = 1
>>> sub = []
>>> while bb < len(stuff2):
... 	try:
... 		sub.append(float(stuff2[bb]) - float(stuff2[aa]))
... 		bb += 1
... 		aa += 1
... 		try:
... 			sub.append(float(stuff2[bb]) - float(stuff2[aa]))
... 			bb += 1
... 			aa += 1
... 		except ValueError:
... 			sub.append("error1")		
... 			bb += 1
... 			aa += 1
... 	except TypeError:		
... 		sub.append("error2")
... 		bb += 1
... 		aa += 1
... 
Traceback (most recent call last):
  File "<interactive input>", line 3, in <module>
ValueError: invalid literal for float(): n/a
>>> sub
[-0.17000000000000004, 'error1']
>>>

thanks for all of your help

I think the exceptions that are being raised are ValueErrors so you only need one try/except block that catches a ValueError. However, I think there is an easier to do what you are trying to do:
[code=python]
stuff2 = ['0.53', '0.36', 'n/a', '0.45', '0.60']
sub = []

for (i, obj) in enumerate(stuff 2):
try:
sub.append(floa t(obj) - float(stuff2[i+1]))
except ValueError:
sub.append("Err or")
[/code]
I'm not sure if that does what you want.

[bvdet]

I noticed in your other thread that you want to include the error in the list 'sub'.[code=Python]stuff2 = ['0.53', '0.36', 'n/a', '0.45', '0.60']
sub = []
for i, item in enumerate(stuff 2):
try:
sub.append(floa t(item) - float(stuff2[i+1]))
except ValueError, e:
sub.append(str( e))
except IndexError:
break
print sub [/code]

>>> [0.1700000000000 0004, 'invalid literal for float(): n/a', 'invalid literal for float(): n/a', -0.1499999999999 9997]