Python 3.X reading null values from a table

Question

let's assume that I have a resultset with a couple of fields. Now one of these fields is coming as 'NULL' or in Python language None. Now I need to create a method to replace whole Nones in a field by a specific word example 'UNKNOWN'. Here is my method.

def definegender(x):
    if x is not None:
      return x
    else:
        x = 'unknown'
        return x

Now testing

z= None
definegender(z)
print('{}'.format(z))

Unfortunately, my approach does not work, please can you guys let me know the best way to create this validation. Thanks

You cannot assign by reference in Python.

willeM_ Van Onsem
– willeM_ Van Onsem

2017-07-25 18:31:56 +00:00
Commented Jul 25, 2017 at 18:31 — willeM_ Van Onsem
– willeM_ Van Onsem, Commented Jul 25, 2017 at 18:31

willeM_ Van Onsem · Accepted Answer · 2017-07-25 19:49:06Z

2

What you aim to do is assign by reference. Is some languages like C, C++ and C# that is possible. In Java and Python it is not. You can alter the state (if you for instance pass a list, you can update the elements, but you cannot set another list to it).

You can however use an assignment operator:

z = None
z = definegender(z)
print('{}'.format(z))

Furthermore you can make the code shorter by using a ternary operator in the definegender function:

def definegender(x):
    return x if x is not None else 'unknown'

edited Jul 25, 2017 at 19:49

answered Jul 25, 2017 at 18:33

willeM_ Van Onsem

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5 Comments

Andres Urrego Angel Over a year ago

Hi buddy, when I try z = definegender(z) without a previous named i got this error NameError: name 'z' is not defined

willeM_ Van Onsem Over a year ago

@AndresAngel: of course you first have to make sure that z is initialized, like in your own code fragment.

Andres Urrego Angel Over a year ago

Well i initialized as z= None but it didnt return 'unknown' :(

willeM_ Van Onsem Over a year ago

@AndresAngel: If I run it on my machine, z is 'undefined' after the call. Are you sure you set z to None and not to the string 'None'?

Andres Urrego Angel Over a year ago

Awesome works like that!! z= None print(definegender(z))

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