[Tutor] TypeError: unsupported operand type(s)

[DL Neil]

On 23/03/20 4:10 AM, SATYABRATA DATTA wrote:
> def x1(ap,dp,ph,e1,e2,e3,e4,e5,y):
>      if Delta(ap,dp,ph,e1,e2,e3,e4,e5,y) >= 0:
>          return 2*(b(ap,dp,ph,e1,e2,e3,e4,e5,y)**3) -
> 9*a*b(ap,dp,ph,e1,e2,e3,e4,e5,y)*c(ap,dp,ph,e1,e2,e3,e4,e5,y) +
> 27*(a**2)*d(ap,dp,ph,e1,e2,e3,e4,e5,y)
>      else:
>          return None
> def y1(ap,dp,ph,e1,e2,e3,e4,e5,y):
>      if Delta(ap,dp,ph,e1,e2,e3,e4,e5,y) >= 0:
>          return 3*np.sqrt(3)*a*np.sqrt(Delta(ap,dp,ph,e1,e2,e3,e4,e5,y))
>      else:
>          return None
> 
> This is creating a problem
> 
>      return
> np.sqrt(x1(ap,dp,ph,e1,e2,e3,e4,e5,y)**2+y1(ap,dp,ph,e1,e2,e3,e4,e5,y)**2)
> TypeError: unsupported operand type(s) for ** or pow(): 'NoneType' and 'int'
> 
> 
> I think the main problem is due to the condition for Delta>=0 which returns
> a None value for some input dataset but I only need the Delta>=0 condition
> values

At one time our programming languages gave us no choice but to return 
'flags' in some cases and valid-output in others. These days to avoid 
the frequent errors experienced working this way, the principle is to 
only ever return one type of data - not sometimes a float and sometimes 
None (etc).

Be aware that in Python, "exceptions" are not necessarily "errors". 
Thus, if the provided-data suits your analysis, there's no problem; but 
if it does not meet the criteria, 'exception[al] processing' side-steps 
the analysis, perhaps by dropping that data-set, without halting execution.

To solve this problem, if the data does not suit your (current) 
analysis, raise a custom exception within the function. In the 
'mainline' code, "wrap" the function calls within a try...except block, 
thus handling 'good data' situations differently from 'bad data'.
-- 
Regards =dn