Change None to Float in List of Strings (Python)

Question

I have a long list of strings in the following format:

    [...
    (0.5, 'house', 'flower'),
    (0.213, 'garden', 'flowerpot'),
    (None, 'mulch', 'hunting'),
    (0.9, 'flower', 'tulip'),
    (0.34, 'party', 'music'),
    (None, 'piano', 'trowel'),
    (0.138, 'fertilizer', 'cow')
    ...]

And before I can sort the list based on the first element, I have to convert the None types to floats. How do I change all the Nones in the list to float 0?

I am trying:

mylist = map(lambda x: 0 if x[0] == None, else x, mylist)

But somewhere I am going wrong with the syntax - anyone have advice for a Pythonic replace all on Nones in the first element of each string for the whole list?

Answer 1

You can use:

list(map(lambda x: (0.0,)+x[1:] if x[0] is None else x,mylist))

which produces:

>>> list(map(lambda x: (0.0,)+x[1:] if x[0] is None else x,mylist))
[(0.5, 'house', 'flower'), (0.213, 'garden', 'flowerpot'), (0.0, 'mulch', 'hunting'), (0.9, 'flower', 'tulip'), (0.34, 'party', 'music'), (0.0, 'piano', 'trowel'), (0.138, 'fertilizer', 'cow')]

The code works as follows: we thus perform a mapping with lambda x: (0.0,)+x[1:] if x[0] is None else x as mapping function.

This is a ternary operator: if the first element x[0] is None, we return (0.0,)+x[1:] so we construct a new tuple with 0.0 as first element, and x[1:] as remaining elements. If the first element is not None, we simply return x.

This will work for every tuple, given it has at least one element. If there can be empty tuples in the list, we can alter the expression to:

list(map(lambda x: (0.0,)+x[1:] if x and x[0] is None else x,mylist))