Bypassing ValueError in a for loop in python

Question

def decade_total_count(decade, name):
    """
    sums up the number of births of the given 
    female baby `name` in a 10-year period
    
    Parameters:
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    decade ... starting year of the decade
    name   ... female name 
           ... str
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    """
    count = 0
    
    for i in range(decade, decade+10):
        yearly = females[(females['name']==name) & (females['year']==i)]['births'].item()
        count = count + yearly
        
    return count

I'm trying to use the function above to get the number of births for any name in the data but my loop stops whenever there's a year that the name does not occur in. In that case, I get this value error:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
/var/folders/yf/s14dt13x11n82t5kg4260v800000gn/T/ipykernel_4325/1603862037.py in <module>
----> 1 total_count('Jennifer')

/var/folders/yf/s14dt13x11n82t5kg4260v800000gn/T/ipykernel_4325/1143784105.py in total_count(name)
     42 
     43     for i in range(start, end, 10):
---> 44         counts.append(decade_total_count(i, name))
     45 
     46     return counts

/var/folders/yf/s14dt13x11n82t5kg4260v800000gn/T/ipykernel_4325/1143784105.py in decade_total_count(decade, name)
     15 
     16     for i in range(decade, decade+10):
---> 17         yearly = females[(females['name']==name) & (females['year']==i)]['births'].item()
     18         count = count + yearly
     19 

~/Desktop/anaconda3/lib/python3.9/site-packages/pandas/core/base.py in item(self)
    329         if len(self) == 1:
    330             return next(iter(self))
--> 331         raise ValueError("can only convert an array of size 1 to a Python scalar")
    332 
    333     @property

ValueError: can only convert an array of size 1 to a Python scalar

How can I bypass the error and keep my loop going even for years that does not contain the given 'name' in my data? I've messed around with try, except, else, and finally clause but somehow it breaks my loop and just returns 0.

score 0 · Answer 1 · answered Apr 02 '22 at 03:58

You haven't shown what you've tried, so I don't know where you're going wrong exactly. However, putting a try-except block within the loop should do the trick:

def decade_total_count(decade, name):
    """
    sums up the number of births of the given 
    female baby `name` in a 10-year period
    
    Parameters:
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    decade ... starting year of the decade
    name   ... female name 
           ... str
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    """
    count = 0
    
    for i in range(decade, decade+10):
        try:
            yearly = females[(females['name']==name) & (females['year']==i)]['births'].item()
            count = count + yearly
        except ValueError as e:
            print(f"Encountered error: {e}. Skipping.")
        
    return count

It's worth noting that this style is known as [Easier to Ask Forgiveness than Permission (EAFP)](https://stackoverflow.com/questions/11360858/what-is-the-eafp-principle-in-python). — Matthew MacGregor, Apr 02 '22 at 04:08

score 0 · Accepted Answer · answered Apr 02 '22 at 04:03

Sorry but I don't have enough information about the variable female.

Try this:

def decade_total_count(decade, name):
    """
    sums up the number of births of the given 
    female baby `name` in a 10-year period
    
    Parameters:
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    decade ... starting year of the decade
    name   ... female name 
           ... str
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    """
    count = 0
    
    for i in range(decade, decade+10):
        try:
            yearly = females[(females['name']==name) & (females['year']==i)]['births'].item()
        except ValueError:
            continue
        count = count + yearly
        
    return count

If a ValueError is raised, just catch it and run next iteration.

Bypassing ValueError in a for loop in python

2 Answers2