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):

stuff2 = ['0.53', '0.36', 'n/a', '0.45', '0.60']
sub = []
for i, item in enumerate(stuff2):
    try:
        sub.append(float(item) - float(stuff2[i+1]))
    except ValueError:
        pass
    except IndexError:        
        break
print sub    

Output:
>>> [0.17000000000000004, -0.14999999999999997]

[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:

stuff2 = ['0.53', '0.36', 'n/a', '0.45', '0.60']
sub = []
 
for (i, obj) in enumerate(stuff2):
    try:
        sub.append(float(obj) - float(stuff2[i+1]))
    except ValueError:
        sub.append("Error")
 

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'.

stuff2 = ['0.53', '0.36', 'n/a', '0.45', '0.60']
sub = []
for i, item in enumerate(stuff2):
    try:
        sub.append(float(item) - float(stuff2[i+1]))
    except ValueError, e:
        sub.append(str(e))
    except IndexError:        
        break
print sub    

>>> [0.17000000000000004, 'invalid literal for float(): n/a', 'invalid literal for float(): n/a', -0.14999999999999997]