将字符串值转换为浮点数

Question

My small script returns a comma separated list of 10 floating point values, loops through them, and holds them in variable vals .

I sum these up into new variable 'total' like this:

total = sum(map(float, vals))

Easy enough, BUT oftentimes None occurs as one or more values in the list,

4.234,None,0.2398,None,None,0.0166666666667,None,None,None,None

then I get the ValueError:

ValueError: could not convert string to float: N

How can I convert these None values to 0 so that the values sum up without error?

Answer 1

total = sum(map(float, filter(None,vals)))

From the docs:

Note that filter(function, iterable) is equivalent to [item for item in iterable if function(item)] if function is not None and [item for item in iterable if item] if function is None.

If vals is a string literal (as DSM hints it looks like it is) use can use the ast library

>>> vals = '[4.234,None,0.2398,None,None,0.0166666666667,None,None,None,None]'
>>> import ast
>>> vals_list = ast.literal_eval(vals)
>>> vals_list
[4.234, None, 0.2398, None, None, 0.0166666666667, None, None, None, None]

Then you can simply apply sum and filter

>>> total = sum(filter(None,vals_list))
>>> total
4.4904666666667

Note -- I did append square brackets to the string, so if they are missing that would be a step you would need

Answer 2

total = sum(float(val) for val in vals if val is not None)

Answer 3

sum(map(lambda x: float(x) if x else 0.0, vals))