Numpy structured array

[Nitram]

Hi all,

I am fairly new to Python and teaching myself. I am working on importing data from a txt file into a NumPy structured array. I have loaded the data in to give three fields: the IATA code of an airport, the airport's latitude, and it's longitude...

 import numpy as np

fname = 'busiest_airports.txt'

dtype1 = np.dtype([('IATA', '|S4'), ('latitude', 'f8'),
                   ('longitude', 'f8')])

a = np.loadtxt(fname, dtype = dtype1, usecols = (0, -2, -1))

print(a) 

This gives me the following array...

 
array([(b'FRA',  50.026,    8.543), (b'DEN',  39.862, -104.673),
       (b'BKK',  13.681,  100.747), (b'SYD', -33.946,  151.177),
       (b'GRU', -23.432,  -46.47 ), (b'CLT',  35.214,  -80.943),
       (b'SFO',  37.619, -122.375), (b'IAH',  29.984,  -95.341),
       (b'ATL',  33.637,  -84.428), (b'ICN',  37.469,  126.451),
       (b'DFW',  32.897,  -97.038), (b'HND',  35.552,  139.78 ),
       (b'LAS',  36.08 , -115.152), (b'PHX',  33.434, -112.012),
       (b'PVG',  31.143,  121.805), (b'DXB',  25.253,   55.364),
       (b'MIA',  25.793,  -80.291), (b'IST',  40.977,   28.815),
       (b'AMS',  52.309,    4.764), (b'CAN',  23.392,  113.299),
       (b'LAX',  33.943, -118.408), (b'CGK',  -6.126,  106.656),
       (b'LHR',  51.477,   -0.461), (b'JFK',  40.64 ,  -73.779),
       (b'SIN',   1.35 ,  103.994), (b'CDG',  49.013,    2.55 ),
       (b'HKG',  22.309,  113.915), (b'ORD',  41.979,  -87.905),
       (b'KUL',   2.746,  101.71 ), (b'PEK',  40.08 ,  116.585)],
      dtype=[('IATA', 'S4'), ('latitude', '<f8'), ('longitude', '<f8')]) 

Now I want to write a function so that I can call the IATA code of an airport and have it's latitude returned. I have tried

 
 def get_lat(x):
    x = a['IATA'][i]
    latitude = a['latitude'][i]
    return latitude 

The idea was to try to set the index 'i' depending on which IATA code is input as the argument of the function. For example an argument of 'BKK' would set i = 1. However I get the error message that 'i' is not defined. Does anyone know how to correctly define the function? Thanks in advance