5.6. The `Effort` class

There is one instance for each circle-year.

`.lat`, `.lon`

These two fields are the composite key used to relate a circle-year to a circle.

`.year_no`

The year number as a string of three digits with left zero fill, e.g., “`008`”. See Section 3.3, “Year number”.

`.year_key`

The year key for this circle-year, left-justified and blank-filled to length 5. S see the discussion of the `year_key` attribute in Section 4.1.7, “Attributes of the `efforts` table”. Example values (where `_` represents a space):

```0001_
0027_
0027b
NMZU_
```
`.yyyymmdd`

Date as a `datetime.date` object.

`.n_obs`

Number of observers as an `int`.

`.ph_tot`, `.ph_foot`, `.ph_car`, `.ph_other`, `.h_fd`, `.h_owl`, `.pm_tot`, `.pm_foot`, `.pm_car`, `.pm_other`, and `.m_owl`

All these hour- and mile-based quantities use Python's `decimal.Decimal` type, with a precision of one digit after the decimal point.

Note that quantities in this type can be formatted using a “`%f`” format, as in this conversational example.

```>>> d1=decimal.Decimal('1.4')
>>> d2=decimal.Decimal('3.47')
>>> d3=d1+d2
>>> d3
Decimal('4.87')
>>> "%6.1f" % d3
'   4.9'
>>> "%6.3f" % d3
' 4.870'
```
`.circle`

The `Circle` instance for to this circle-year.

`.censuses`

An iterator that produces all the `Census` instances for this circle-year.