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A currency field and support for ``z3c.form``.

Project Description

A package implementing a currency field for zope.schema and support for using the field with z3c.form.

Detailed Documentation

The Currency Field

The currency field is a numerical field, specifically designed to manage monetary values.

>>> from z3c.currency import field, interfaces
>>> price = field.Currency(
...    title=u'Price',
...    description=u'The price of the item.')

Besides the common attributes, the currency field also provides two additional attributes, the precision and unit. The precision is intended to allow for specifying whether the value is provided whole units or 1/100th of the whole unit – in the US dollar and cents. By default this field is set to cents:

>>> price.precision is interfaces.CENTS
True

It can be set to be dollars:

>>> price.precision = interfaces.DOLLARS
>>> price.precision is interfaces.DOLLARS
True

For financial applications, we also sometimes needsub-cents:

>>> price.precision = interfaces.SUBCENTS
>>> price.precision is interfaces.SUBCENTS
True

Note: Is there a more “internationalized” word for the whole unit of a currency?

The unit specifies the symbol of the currency used. It is also used for formatting the numerical value to a string.

>>> price.unit
u'$'
>>> price.unit = u''
>>> price.unit
u'\xe2\x82\xac'

Of course, both of those attributes are available as constructor arguments:

>>> price = field.Currency(
...    title=u'Price',
...    description=u'The price of the item.',
...    precision=interfaces.DOLLARS,
...    unit=u'')
>>> price.precision is interfaces.DOLLARS
True
>>> price.unit
u'\xe2\x82\xac'

Let’s now have a look at the validation. First of all, the value must always be a decimal:

>>> import decimal
>>> price.validate(decimal.Decimal('12'))
>>> price.validate(12)
Traceback (most recent call last):
...
WrongCurrencyType: int
>>> price.validate(12.0)
Traceback (most recent call last):
...
WrongCurrencyType: float

Also, when the precision is set to DOLLARS as it is the case here, the value must be a whole number:

>>> price.validate(decimal.Decimal('12'))
>>> price.validate(decimal.Decimal('12.01'))
Traceback (most recent call last):
...
IncorrectValuePrecision: 0
>>> price.validate(decimal.Decimal('12.00'))
Traceback (most recent call last):
...
IncorrectValuePrecision: 0

When the precision is set to cents,

>>> price.precision = interfaces.CENTS

then values only with two decimal places are accepted:

>>> price.validate(decimal.Decimal('12.00'))
>>> price.validate(decimal.Decimal('12'))
Traceback (most recent call last):
...
IncorrectValuePrecision: 1
>>> price.validate(decimal.Decimal('12.0'))
Traceback (most recent call last):
...
IncorrectValuePrecision: 1

If we allow sub-cents,

>>> price.precision = interfaces.SUBCENTS

any precision is allowed:

>>> price.validate(decimal.Decimal('12.0'))
>>> price.validate(decimal.Decimal('12'))
>>> price.validate(decimal.Decimal('12.00001'))

If the field is not required, …

>>> price.required = False

let’s make sure that the validation still passes.

>>> price.validate(None)

Note that the IFromUnicode interface is purposefully not supported:

>>> price.fromUnicode
Traceback (most recent call last):
...
AttributeError: 'Currency' object has no attribute 'fromUnicode'

z3c.form Support

This package also provides support for integration with the z3c.form package. In particular it implements a data converter from the Currency field to any widget accepting a unicode string.

>>> from z3c.currency import converter
>>> conv = converter.CurrencyConverter(price, None)
>>> conv
<DataConverter from Currency to NoneType>

The converter easily produces a string from any value:

>>> conv.toWidgetValue(decimal.Decimal(12))
u'12'
>>> conv.toWidgetValue(decimal.Decimal(1200))
u'1,200'
>>> conv.toWidgetValue(decimal.Decimal(-12))
u'-12'
>>> conv.toWidgetValue(decimal.Decimal('-12.0'))
u'-12.00'
>>> conv.toWidgetValue(decimal.Decimal('-12.00'))
u'-12.00'

Note that always two decimal places are printed. You can also set the precision to DOLLARS:

>>> conv.field.precision = interfaces.DOLLARS
>>> conv.toWidgetValue(decimal.Decimal(12))
u'12'
>>> conv.toWidgetValue(decimal.Decimal('12.00'))
u'12'

Let’s try sub-cents as well:

>>> conv.field.precision = interfaces.SUBCENTS
>>> conv.toWidgetValue(decimal.Decimal('12.00'))
u'12.00'
>>> conv.toWidgetValue(decimal.Decimal('12'))
u'12'
>>> conv.toWidgetValue(decimal.Decimal('12.0001'))
u'12.0001'

If the value is missing, then handle it gracefully.

>>> conv.toWidgetValue(None)
u''

Let’s now parse a value. The parser is a little bit flexible, not only accepting the output values, …

>>> conv.field.precision = interfaces.CENTS
>>> conv.toFieldValue(u'12')
Decimal('12.00')
>>> conv.toFieldValue(u'1,200')
Decimal('1200.00')
>>> conv.toFieldValue(u'-12')
Decimal('-12.00')
>>> conv.toFieldValue(u'-12.00')
Decimal('-12.00')
>>> conv.field.precision = interfaces.DOLLARS
>>> conv.toFieldValue(u'12')
Decimal('12')
>>> conv.toFieldValue(u'12.00')
Decimal('12')
>>> conv.field.precision = interfaces.SUBCENTS
>>> conv.toFieldValue(u'12')
Decimal('12')
>>> conv.toFieldValue(u'12.00')
Decimal('12.00')
>>> conv.toFieldValue(u'12.0000')
Decimal('12.0000')
>>> conv.toFieldValue(u'12.0001')
Decimal('12.0001')

but also other input values:

>>> conv.toFieldValue(u'1200')
Decimal('1200')

If the browser sends an empty string, then handle it gracefully.

>>> conv.toFieldValue(u'')

CHANGES

1.1.1 (2015-11-09)

  • Standardize namespace __init__

1.1.0 (2013-09-27)

  • Added new precision value “sub-cents” (interfaces.SUBCENTS), which allows precision beyond pennies, which is needed for financial and other business applications.

1.0.0 (2013-08-16)

  • Updated Trove classifiers.
  • Moved code to GitHub.
  • Changed validation to raise custom validation errors, since the upstream code looks at the doc string of the exception instead of the first argument.
  • Improved converter to
    • Ensure proper precision of decimal after initial parsing.
    • Format the value to the proper precision.
  • Changed “precision” field in ICurrency interface to be a choice, so that UIs generate nicely.
  • Cleaned up code a little bit.

0.1.0 (2007-09-12)

  • Initial Release
    • Implementation of Currency field supporting precision and a unit.
    • Implementation of data converter.
Release History

Release History

This version
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1.1.1

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1.1.0

History Node

1.0.0

History Node

0.1.0

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