Converting all non-numeric to 0 (zero) in Python

Question

I'm looking for the easiest way to convert all non-numeric data (including blanks) in Python to zeros. Taking the following for example:

someData = [[1.0,4,'7',-50],['8 bananas','text','',12.5644]]

I would like the output to be as follows:

desiredData = [[1.0,4,7,-50],[0,0,0,12.5644]]

So '7' should be 7, but '8 bananas' should be converted to 0.

Answer 1

import numbers
def mapped(x):
    if isinstance(x,numbers.Number):
        return x
    for tpe in (int, float):
        try:
            return tpe(x)
        except ValueError:
            continue
    return 0
for sub  in someData:
    sub[:] = map(mapped,sub)

print(someData)
[[1.0, 4, 7, -50], [0, 0, 0, 12.5644]]

It will work for different numeric types:

In [4]: from decimal import Decimal

In [5]: someData = [[1.0,4,'7',-50 ,"99", Decimal("1.5")],["foobar",'8 bananas','text','',12.5644]]

In [6]: for sub in someData:
   ...:         sub[:] = map(mapped,sub)
   ...:     

In [7]: someData
Out[7]: [[1.0, 4, 7, -50, 99, Decimal('1.5')], [0, 0, 0, 0, 12.5644]]

if isinstance(x,numbers.Number) catches subelements that are already floats, ints etc.. if it is not a numeric type we first try casting to int then to float, if none of those are successful we simply return 0.

Answer 2

Another solution using regular expressions

import re

def toNumber(e):
    if type(e) != str:
        return e
    if re.match("^-?\d+?\.\d+?$", e):
        return float(e)
    if re.match("^-?\d+?$", e):
        return int(e)
    return 0

someData = [[1.0,4,'7',-50],['8 bananas','text','',12.5644]]
someData = [map(toNumber, list) for list in someData]
print(someData)

you get:

[[1.0, 4, 7, -50], [0, 0, 0, 12.5644]]

Note It don't works for numbers in scientific notation