"negative seek position" error

I’m trying to open ERA5 pressure level data inside a grib-file downloaded from the CDS (see the bottom of the post for the download-command).

I’m trying to open the data at different time-indices like this, which works fine for any value of t between 0 and 18:

ds = cfgrib.open_file(r'F:\era5_for_wam2\pl_2008_01.grib')
var = ds.variables['q']

t = 18
q = var.data[t,:,:,:]

However, as soon as t is larger than 18, e.g.:

q = var.data[19,:,:,:]

I get the following error:

Traceback (most recent call last):

  File "<ipython-input-30-a8a5f441ed1e>", line 1, in <module>
    q = var.data[19,:,:,:]

  File "C:\ProgramData\Miniconda3\lib\site-packages\cfgrib\dataset.py", line 259, in __getitem__
    message = self.stream.message_from_file(file, offset=offset[0])

  File "C:\ProgramData\Miniconda3\lib\site-packages\cfgrib\messages.py", line 244, in message_from_file
    return self.message_class.from_file(file=file, offset=offset, **kwargs)

  File "C:\ProgramData\Miniconda3\lib\site-packages\cfgrib\messages.py", line 66, in from_file
    file.seek(offset)

ValueError: negative seek position -5

I have many files like the one in this example (pl_2008_01.grib, pl_2008_02.grib, pl_2008_03.grib, etc.), and each of them crashes when trying to open data with a t > 18.

Any ideas what is causing this and how to solve this? I’m on a windows machine, Python=3.7.1 and cfgrib=0.9.6

I’m getting my grib files like this:

import cdsapi
c = cdsapi.Client()
c.retrieve(
            'reanalysis-era5-pressure-levels',
            {
                'product_type':'reanalysis',
                'format':'grib',
                'pressure_level':[
                    '50','150','250','350',
                    '450','550','650',
                    '750','800','850',
                    '900','950','1000'
                ],
                'month':'1',
                'day':[
                '01','02','03',
                '04','05','06',
                '07','08','09',
                '10','11','12',
                '13','14','15',
                '16','17','18',
                '19','20','21',
                '22','23','24',
                '25','26','27',
                '28','29','30',
                '31'
            ],
                'time':
                    [
                    '00:00','01:00','02:00',
                    '03:00','04:00','05:00',
                    '06:00','07:00','08:00',
                    '09:00','10:00','11:00',
                    '12:00','13:00','14:00',
                    '15:00','16:00','17:00',
                    '18:00','19:00','20:00',
                    '21:00','22:00','23:00',],
                'year':'2008',
                'variable':[
                    'specific_humidity','u_component_of_wind','v_component_of_wind',
                    'vertical_velocity'
                ]
            },
            r'F:\era5_for_wam2\pl_2008_01.grib')

[bertcoerver]

Just in case anyone else has this problem:

I had installed ecCodes with conda-forge with:

conda install -c conda-forge eccodes

but I didn’t set the environmental variables ECCODES_DEFINITION_PATH and ECCODES_SAMPLES_PATH (see here for more info) correctly. Doing that solved the issue.

[alexamici]

@bertcoerver:

1. Did you remove the .idx file and retry?
2. After doing 1. and still getting a negative seek error, can you attach the .idx file to the issue?

Thanks!