html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/issues/1598#issuecomment-333175863,https://api.github.com/repos/pydata/xarray/issues/1598,333175863,MDEyOklzc3VlQ29tbWVudDMzMzE3NTg2Mw==,13837821,2017-09-29T16:37:07Z,2017-09-29T16:37:20Z,CONTRIBUTOR,"@jhamman In brief, it's weird. 

Engine | encoding['_FillValue'] = False | Do nothing
----- | ----- | -----
netCDF4 | Filling off | Filling on
scipy | Filling off | Filling off
h5netcdf | Filling on | Filling off

So, this is some peculiar behavior. Setting `_FillValue` to `False` works for netCDF4 (as we have seen), has no effect using the scipy engine, and seems to do the opposite of intended for h5netcdf.

**Code below:**

```
import xarray as xr
import numpy as np
import pandas as pd

ds = xr.Dataset({'foo': (('x', 'y'), np.random.rand(4, 5))},
                 coords={'x': [10, 20, 30, 40],
                         'y': pd.date_range('2000-01-01', periods=5),
                        'z': ('x', list('abcd'))})

ds.to_netcdf('notset_scipy.nc', engine='scipy')
ds.to_netcdf('notset_netcdf4.nc', engine='netcdf4')
ds.to_netcdf('notset_h5netcdf.nc', engine='h5netcdf')

ds.y.encoding['_FillValue'] = False

ds.to_netcdf('False_scipy.nc', engine='scipy')
ds.to_netcdf('False_netcdf4.nc', engine='netcdf4')
ds.to_netcdf('False_h5netcdf.nc', engine='h5netcdf')
```

**netCDF4**
```
$ ncinfo -v y notset_netcdf4.nc 
<type 'netCDF4._netCDF4.Variable'>
int64 y(y)
    units: days since 2000-01-01 00:00:00
    calendar: proleptic_gregorian
unlimited dimensions: 
current shape = (5,)
filling on, default _FillValue of -9223372036854775806 used
```
```
$ ncinfo -v y False_netcdf4.nc 
<type 'netCDF4._netCDF4.Variable'>
int64 y(y)
    units: days since 2000-01-01 00:00:00
    calendar: proleptic_gregorian
unlimited dimensions: 
current shape = (5,)
filling off
```

**scipy**
```
$ ncinfo -v y notset_scipy.nc 
<type 'netCDF4._netCDF4.Variable'>
int32 y(y)
    units: days since 2000-01-01 00:00:00
    calendar: proleptic_gregorian
unlimited dimensions: 
current shape = (5,)
filling off
```

```
$ ncinfo -v y False_scipy.nc 
<type 'netCDF4._netCDF4.Variable'>
int32 y(y)
    units: days since 2000-01-01 00:00:00
    calendar: proleptic_gregorian
    _FillValue: 0
unlimited dimensions: 
current shape = (5,)
filling off
```

**h5netcdf**
```
$ ncinfo -v y notset_h5netcdf.nc 
<type 'netCDF4._netCDF4.Variable'>
int64 y(y)
    units: days since 2000-01-01 00:00:00
    calendar: proleptic_gregorian
unlimited dimensions: 
current shape = (5,)
filling off
```

```
$ ncinfo -v y False_h5netcdf.nc 
<type 'netCDF4._netCDF4.Variable'>
int64 y(y)
    _FillValue: 0
    units: days since 2000-01-01 00:00:00
    calendar: proleptic_gregorian
unlimited dimensions: 
current shape = (5,)
filling on
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,261403591
https://github.com/pydata/xarray/issues/1598#issuecomment-333165596,https://api.github.com/repos/pydata/xarray/issues/1598,333165596,MDEyOklzc3VlQ29tbWVudDMzMzE2NTU5Ng==,13837821,2017-09-29T15:55:22Z,2017-09-29T15:55:22Z,CONTRIBUTOR,"> Allowing {'_FillValue': False} to indicate that _FillValue should not be included would be a simple, easy fix, so we should probably do that regardless.

Correct me if you're talking about something different, but xarray already supports setting `_FillValue` to `False` to turn off filling. (Is there any use case where filling remains on but without a valid `_FillValue`?) For example, I have a netCDF processing routine using xarray. In the code I have the line for the `lon` dimension:

    ds.lon.encoding['_FillValue'] = False

Which, for the relevant dimension, yields in ncinfo:

```
$ ncinfo -v lon yesfalse.nc 
<type 'netCDF4._netCDF4.Variable'>
float64 lon(lon)
    units: degrees_east
    long_name: Longitude
    epic_code: 502
unlimited dimensions: 
current shape = (1,)
filling off
```

If I comment out that line in my processing routine, I get the following:

```
$ ncinfo -v lon nofalse.nc 
<type 'netCDF4._netCDF4.Variable'>
float64 lon(lon)
    _FillValue: nan
    units: degrees_east
    long_name: Longitude
    epic_code: 502
unlimited dimensions: 
current shape = (1,)
filling on
```
 
I agree that changing from `False` to `None` does make better semantic sense.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,261403591