Time for action – creating a record data type

The record data type is a heterogeneous data type—think of it as representing a row in a spreadsheet or a database. To give an example of a record data type, we will create a record for a shop inventory. The record contains the name of the item, a 40-character string, the number of items in the store represented by a 32-bit integer, and, finally, a price represented by a 32-bit float. These consecutive steps show how to create a record data type:

  1. Create the record:
    In: t = dtype([('name', str_, 40), ('numitems', int32), ('price', float32)])
In: t
Out: dtype([('name', '|S40'), ('numitems', '<i4'), ('price', '<f4')])
  2. View the type (we can view the type of a field as well):
    In: t['name']
Out: dtype('|S40')

If you don't give the array() function a data type, it will assume that it is dealing with floating point numbers. To create the array now, we really have to specify the data type; otherwise, we will get a TypeError:

In: itemz = array([('Meaning of life DVD', 42, 3.14), ('Butter', 13, 2.72)], dtype=t)
In: itemz[1]
Out: ('Butter', 13, 2.7200000286102295)

What just happened?

We created a record data type, which is a heterogeneous data type. The record contained a name as a character string, a number as an integer, and a price represented by a float. The code for this example can be found in the record.py file in this book's code bundle.

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