python mysqldb single row/column returned tuple value

Question

db_quote_cursor.execute("""select lastince 
                           from `here` 
                           order by `date` desc, `time` desc 
                           limit 1""")
thisout= db_quote_cursor.fetchone()

thisout is a single value that is a float. I need to do calculations on it but can't cast it as a float in the tuple.

!work(pleasework=float(thisout[0]))

I tried converting it to a list, that didn't work either. How do I directly access the value within the tuple when I don't want/need to loop through it? Or something else maybe...

Here's what I get back from the database:

print(this out)
# -> ((Decimal('118'),),)

And this is the error I'm getting:

>>> result = float(thisout[0]) 
Traceback (most recent call last): File "file.1.py", line 56, in <module> 
TypeError: float() argument must be a string or a number

Please post the exact error message you're getting. Thank you. — mechanical_meat
– mechanical_meat, Commented Mar 20, 2012 at 17:52
((Decimal('118'),),) (This is "print(this out)") Traceback (most recent call last): File "file.1.py", line 56, in <module> result=float(thisout[0]) TypeError: float() argument must be a string or a number — Pauly
– Pauly, Commented Mar 20, 2012 at 19:26
Ah, so it's already in a usable format for your calculations. — mechanical_meat
– mechanical_meat, Commented Mar 20, 2012 at 19:28

mechanical_meat · Accepted Answer · 2012-03-20 19:41:29Z

1

The situation is more clear now that you posted the traceback. Thank you.

You're getting back a Decimal object.
This is just as good, in fact, better than a float.

You needn't convert it, and may simply begin your calculations:

thisout[0] += 1 # works fine

However, note that you cannot do:

thisout[0] += 1.0 # this is a TypeError

In the above case you would do instead:

import decimal as dc
thisout[0] += dc.Decimal('1.0')

answered Mar 20, 2012 at 19:41

mechanical_meat

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4 Comments

Pauly Over a year ago

it may be better, but not for the calculation I need to do: result=sqrt(thisout[0]) TypeError: a float is required

mechanical_meat Over a year ago

@Pauly: for precisely this reason the Python core developers have created for you a sqrt() method. So you may simply do: result = thisout[0].sqrt()

Pauly Over a year ago

thank you for the help. However nothing seems to work. result=thisout[0].sqrt() AttributeError: 'tuple' object has no attribute 'sqrt'

mechanical_meat Over a year ago

You're not using fetchone() any longer. Instead do this: thisout[0][0].sqrt()

Collin Green · Accepted Answer · 2012-03-20 18:01:31Z

0

If the result is simply a 1-tuple, you can access it as bernie says (and your code apparently tries) with thisout[0]. I'm guessing you're having a different error when trying to parse the float; post the stacktrace or the exception.

answered Mar 20, 2012 at 18:01

Collin Green

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1 Comment

Pauly Over a year ago

result=sqrt(thisout[0]) TypeError: a float is required

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