How to iterate over latitude longitude values of a grib2 file?

I'm trying to get the uvIndex of all the lat,lng present in a grib2 file. This is the link from where I'm getting the file. The problem is I'm not able to understand the structure of the file so that I can get the data. I'm using pygrib to read the file.

Here's the code I've tried:

grbs = pygrib.open('uv.t12z.grbf01.grib2')
grb = grbs.select(name='UV index')[0]
print grb.data(23.5,55.5)

What I'm trying to achieve is either iterate over all the lat longs and print the corresponding uvIndex value or enter a lat long and get the corresponding value. Read the docs of pygrib but couldn't find any suitable command that will serve my purpose. Please help.

Solution

You have to iterate though GRIB file and find desirable record, then get data, like here:

for g in grbs:
    print g.shortName, g.typeOfLevel, g.level # print info about all GRIB records and check names 
    if (g.shortName == shortName and g.typeOfLevel == typeOfLevel and g.level == level):
        tmp = np.array(g.values)
        # now work with tmp as numpy array

To get lat and lon arrays use: lt, ln = g.latlons(), g - element of grbs.

Read the examples in Section python at https://software.ecmwf.int/wiki/display/GRIB/GRIB+API+examples (pygrib use this library to read GRIB).

The fastest way to get data from large GRIB file is to make index:

# use attributes what you want to build index
indx = pygrib.index(gribfile,'typeOfLevel','level','parameterName') 

# important: msg is an array and may have more then one record
# get U wind component on 10 m above ground
msg = indx.select(level = 10, typeOfLevel = "heightAboveGround",
 parameterName = "U U-component of wind m s**-1")
u10 = np.array(msg[0].values)
# get V wind component on 10 m above ground
msg = indx.select(level = 10, typeOfLevel = "heightAboveGround",
 parameterName = "V V-component of wind m s**-1")
v10 = np.array(msg[0].values)