x = 100
with open("C:/path/to/file/you/want/to/copy/from",'r') as f1:
data = f1.readlines()
with open("C:/path/to/file/you/want/to/copy/from",'w') as f1:
for line in data[x:]:
f1.write(line)
with open("C:/path/to/file/you/want/to/copy/to",'w') as f2:
for line in data[:x]:
f2.write(line)