Lambda sorting in Python 3

Question

I was working on python2 for my project.Now I want to migrate from python2 to python3. I am getting syntax error while writing the for loop code snippet given below.I'm bit confused where I went wrong.

Code :

for k, val in sorted(datasource_columns.iteritems(), key=lambda(
                            k, v): sort_order.index(k)):
                        # columns.add_column(key, sorted(val))
                        columns.add_column(k, val)

where , sort_order = ['Name', 'Data Type', 'Type', 'Role']

Answer 1

As already said, iteritems() will be a problem, but you mention a syntax error, which comes from the lambda declaration with parenthesis:

Change:

key=lambda(k, v): sort_order.index(k)

To:

key=lambda k, v: sort_order.index(k)

But you may as well write this more efficient code:

for key in sort_order:
    val = datasource_columns.get(key)
    if val is not None: # to avoid getting None values in your columns
        columns.add_column(key, val)

In the future, please post the actual stacktrace whenever you get an exception, this makes it a lot easier to understand any issue.

Answer 2

    key=lambda k, v: sort_order.index(k) 

does not work. TypeError: () missing 1 required positional argument: v

The needed change for Python 3 would be:

    test_list.sort(key = lambda args : sort_order.index(args[0])) 

Answer 3

Not sure what changed exactly but lambda (k, v): sort_order.index(k) is invalid syntax in python3. You can use lambda k, v: sort_order.index(k) instead.