Please, help to identify the mistake in the code

[Alberto]

Dear Python Users,

Please, help to identify where is my mistake in the code. What I am trying to do is to write the info (lines 1-3) into txt file.
However, when I run this code the python never executes it, it continues to run forever.

tsv = [20, 31, 52, 73]
forecast = [0, 20, 31, 52]
forecast_error = [0, 0, 0, 0]

for x in range(0, len(tsv)):
   forecast_error[x] = tsv[x] - forecast[x]

F1 = open('C:\\Users\\Documents\\Exercise2\\fixeddata.txt', 'w')
#example line
#37        52        352
#          111111111122222222222
#0123456789012345678901234567890

for x in range(0, len(tsv)):
   strrec = ""
   #handle tsv
   str1 = str(tsv[x])
   while len(str1) < 10:
       str1 = str1 + ""
   strrec = strrec + str1 
   #handle forecast
   str1 = str(forecast[x])
   while len(str1) < 10:
       str1 = str1 + ""
   strrec = strrec + str1
   #handle forecast error
   str1 = str(forecast_error[x])
   while len(str1) < 10:
       str1 = str1 + ""
   strrec = strrec + str1
   strrec = strrec + "\n"
   F1.write(strrec)
       
F1.close()