#30290: Documentation should make clear that values on DecimalField is better
to be
passed as strings
-----------------------------------------+------------------------
Reporter: kantale | Owner: nobody
Type: Uncategorized | Status: new
Component: Documentation | Version: 2.1
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 1
UI/UX: 0 |
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On the documentation of
[https://docs.djangoproject.com/en/2.1/ref/models/fields/#django.db.models.DecimalField
DecimalField] it does not mention that passing values as string instead of
float has a significant difference. A user that tests the code in the
documentation might come to a surprise to find that the following part
raises a ValidationError:
{{{
class A(models.Model):
# A DecimalField as mentioned on the doc
# "For example, to store numbers up to 999 with a resolution of 2
decimal places, you’d use:"
f = models.DecimalField(max_digits=5, decimal_places=2)
}}}
{{{
A(f=10.1).clean_fields() # This raises the following exception:
django.core.exceptions.ValidationError: {'f': ['Ensure that there are no
more than 2 decimal places.']}
}}}
If the value of f is passed as string, then it works as expected.
{{{
A(f="10.1").clean_fields()
}}}
There is a very subtle reference about this on the documentation of the
[https://docs.python.org/3/library/decimal.html decimal module]:
{{{
>>> Decimal(3.14)
Decimal('3.140000000000000124344978758017532527446746826171875')
}}}
See also discussion in SO: https://stackoverflow.com/questions/52376693
/django-strange-decimalfield-validation
--
Ticket URL: <https://code.djangoproject.com/ticket/30290>
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