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54 lines
1.6 KiB
Markdown
54 lines
1.6 KiB
Markdown
# Class ValueTuple
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A value, along with the unit it is in, can be represented by a 3-way
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tuple called a "value tuple". They are used throughout WeeWX. All
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WeeWX routines can accept a simple unadorned 3-way tuple as a value
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tuple, but they return the type `ValueTuple`. It is useful
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because its contents can be accessed using named attributes. You can
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think of it as a unit-aware value, useful for converting to and from
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other units.
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The following attributes, and their index, are present:
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<table>
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<tr>
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<th>Index</th>
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<th>Attribute</th>
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<th>Meaning</th>
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</tr>
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<tr>
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<td>0</td>
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<td class="code">value</td>
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<td>The data value(s). Can be a series (e.g., <span class="code">[20.2, 23.2, ...]</span>) or a scalar
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(e.g., <span class="code">20.2</span>)
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</td>
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</tr>
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<tr>
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<td>1</td>
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<td class="code">unit</td>
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<td>The unit it is in (<span class="code">"degree_C"</span>)</td>
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</tr>
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<tr>
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<td>2</td>
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<td class="code">group</td>
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<td>The unit group (<span class="code">"group_temperature"</span>)</td>
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</tr>
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</table>
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It is valid to have a datum value of `None`.
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It is also valid to have a unit type of `None` (meaning there is no
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information about the unit the value is in). In this case, you won't be
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able to convert it to another unit.
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Here are some examples:
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``` python
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from weewx.units import ValueTuple
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freezing_vt = ValueTuple(0.0, "degree_C", "group_temperature")
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body_temperature_vt = ValueTuple(98.6, "degree_F", "group_temperature")
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station_altitude_vt = ValueTuple(120.0, "meter", "group_altitude")
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```
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