numbers in string come out as "not numbers" or fals - Python

So, I have a list of strings in python, and I am trying to find which keys are numbers.
I am trying to use list.[key].isdigit() but it only works with '0'
For instance:

list = ['0', '0', '0', '0.450000000000000', '0', '0', '0', '0.550000000000000']

will only determine that '0' is a digit, but '0.45' and '0.55' are not.
How can I fix this problem?

Thank you very much