Question

i wish to improve the following function. Given a Pixel data types in GDAL (ex: "Int16") resturn a code number.

def GDAL_data_type(dataType):
    dtypes = {
        "Unknown": 0,
        "Byte": 1,
        "UInt16": 2,
        "Int16": 3,
        "UInt32": 4,
        "Int32": 5,
        "Float32": 6,
        "Float64": 7,
        "CInt16": 8,
        "CInt32": 9,
        "CFloat32": 10,
        "CFloat64": 11
        }
    return dtypes[dataType]

GDAL_data_type("Int16")
3

I wish to insert a error message in the function where if you type a dataType different, the error message say:

raise SystemExit('Pixel data type no recognized %s' % dataType)

I wish to ask the best way to insert this error message in my function. Thanks in advance

Answer 1

Wrap the dictionary lookup in a try block, catch the keyerror exception, and raise your own from the catch block:

try:
  return dtypes[dataType]
except KeyError:
  raise ...

EDIT

Or more fully:

def GDAL_data_type(dataType):
    dtypes = {
        "Unknown": 0,
        "Byte": 1,
        "UInt16": 2,
        "Int16": 3,
        "UInt32": 4,
        "Int32": 5,
        "Float32": 6,
        "Float64": 7,
        "CInt16": 8,
        "CInt32": 9,
        "CFloat32": 10,
        "CFloat64": 11
        }
    try:
        return dtypes[dataType]
    except KeyError:
        raise ...