py_wlc.generic package

Submodules

py_wlc.generic.growth module

Generic functionality for modelling growth series.

class py_wlc.generic.growth.IndexSeries(base_year, rates, initial_value, year_zero=None)

Bases: object

Growth rates and factors for indexation series.

The _rates dictionary is fully-populated at initialisation, but the _values dictionary is filled lazily - values are only calculated as needed.

The class supports a Mapping-like interface; factors can be accessed with value = growth_rate[year] or value = growth_rate.get(year, default).

Note

The term ‘relative year’ refers to the year relative to year_zero e.g. 3. The term ‘absolute year’ refers to a calendar year, e.g. 2013. Relative years are used internally, absolute years for the external interface.

Parameters:

• base_year (int) – the year in which the value is equal to the initial_value
• rates (dict of int: float) – the growth rates to use, keyed by relative year
• initial_value (float) – the first value for the output series.
• year_zero (int, optional) – the zeroth year for accessing growth rates. Defaults to base_year.

base_year

int

The base year for growth, i.e. the year in which the value is the initial_value.

year_zero

int

The zeroth year for growth, i.e. the year from which the rates are selected from _rates.

_rates

dict of int: float

The growth rates, where the key is the relative start year and the value is the rate to apply.

_initial_rate

float

The growth rate corresponding to the first year in the rates dictionary.

_final_rate

float

The growth rate corresponding to the last year in the rates dictionary.

_values

dict of int: float

The values, keyed by year.

get(year, default=None)

Retrieve value or supplied default for given year.

Parameters:

• year (int) – The year to retrieve the value for.
• default (float or None, optional) – The value to return if retrieval fails. Defaults to None.

Returns:

The retrieved or default value.

Return type:

float or None

rate(year)

The rate used in the specified year.

Parameters:year (int) – The year to retrieve the rate for. Returns:The rate used in that year. Return type:float

Module contents

Generic functionality supporting the core modelling.

class py_wlc.generic.ExtendedDict

Bases: dict

Dictionary subclass that provides values beyond defined keys.

Provides values outside the predefined range, according to the following rules:

• If the key is larger than the largest key in the dictionary, the value from the largest key is returned.
• If the key is smaller than the smallest key in the dictionary, the value from the smallest key is returned.
• If the key is between the smallest and largest keys in the dictionary but no value is found, a KeyError occurs.

copy()

Create a copy of the extended dictionary.

Returns:A new class instance. Return type:ExtendedDict

get(key, default=None)

Return either the value of the key, or the default.

Parameters:

• key – The key to return the value of.
• default – The object to return if the key is not found.

Returns:

Either the value for the specified key, or default.