How to split chunks of xy data into lists between isalpha() and newline \n

So I've got a cleaned up datafile of number strings, representing coordinates for polygons. I've had experience assigning one polygon's data in a datafile into a column and plotting it in numpy/matplotlib, but for this I have to plot multiple polygons from one datafile separated by headers. The data isn't evenly sized either; every header has several lines of data in two columns, but not the same amount of lines.

i.e.

PolyOne
319547.04899999965,673790.8118999992
319553.2614000002,673762.4122000001
319583.4143000003,673608.7760000005
319623.6182000004,673600.1608000007
319685.3598999996,673600.1608000007
##etc


PolyTwoandabit
319135.9966000002,673961.9215999991
319139.7357999999,673918.9201999996
319223.0153000001,673611.6477000006
319254.6040000003,673478.1133999992
##etc etc


PolyOneHundredFifty
##etc

My code so far involves cleaning the original dataset up to make it like you see above;

data_easting=[]
data_northing=[]

County = open('counties.dat','r')

for line in County.readlines():

    if line.lstrip().startswith('#'):
        print ('Comment line ignored and leading whitespace removed')
        continue

    line = line.replace('/','and').replace(' ','').replace('[','').replace(']','').replace('),(','\n')
    line = line.strip('()\n')
    print (line)

    if line.isalpha():
        print ('Skipped header: '+ line)
        continue

I've been using isalpha(): to ignore the headers for each polygon so far, and I was planning on using if line == '\n': continue and line.split(',') to ignore the newlines between data and begin splitting the Easting and Northing lists. I've already got the numpy and matplotlib section of the code (not shown) sorted to make 1 polygon, but I don't know how to implement it to plot multiple arrays/multiple polygons.

I realised early on though that if I tried to assign all the data to the 2 x and y lists, that would just make one large unending polygon that will make a spaghetti mess of my plot as imaginary lines will be drawn to connect them up.

I want to use the isalpha() section to instead identify and make a Dictionary or List of the polygon names, and attach an array for each polygon datablock to that, but I'm not sure of how to implement it (or if you even can). I'm also not certain how to make it stop loading data into a list at the end of a polygon datablock (maybe if line == '\n': break? but how to make it start and stop again 149 more times for each other chunk?).

To make it a bit more difficult, there is 150 polygons with x and y data in this file, so making 150 x and y lists for each individual polygon and writing specific code for each wouldn't be very efficient.

So, how do I basically do:

if line.isalpha():
    #(assign to a Counties dictionary or a list as PolyOne, PolyTwo,...PolyOneHundredFifty)
    #(a way of getting the data between the header and newline into a separate list)
    #(a way to relate that PolyOne Data list of x and y to the dictionary "PolyOne")

if line == '\n':
    #(break? continue?)
    #(then restart and repeat for PolyTwo,...PolyOneHundredFifty)

line.split (',')
data_easting.append(x) #x1,x2,...x150?
data_northing.append(y) #y1,y2,y150?)

Is there a way of doing what I intend? How would I go about that without pandas?

Thanks for your time.