function for extracting data from lists

[ibreeden]

Nono, this is what you do:

y = []       # create empty list with name "y"
...
y=x[key]     # y = 19.75; Now y is a floating point number
y.append(x)  # append something to a float???

append() is a method of list. So you must do:

y = []
...
y.append(x[key])

... and after the for-loop has finished you will have a list with all the data that you want.