Remove line breaks from a BIG text file

[Chris9]

I need to remove line breaks from a large ASCII table, but get a MemoryError. The data is an ASCII grid: the header takes up the first 6 lines followed by 22000 rows of data. I want to remove the line breaks from the table part of the file while leaving the first 6 line breaks. The following code works for small files but runs out of memory (at the 3rd line) for large files: (thanks to Zhaphod and Bvdet from an earlier post)

f1 = open(fn1) 
f2 = open(fn2, 'w') 
outputlist = [line.strip() for line in f1] 

f2.write("\n".join(outputlist[:6]))
f2.close() 
f2 = open(fn2, 'a')

f2.write("\n")
f2.write(" ".join(outputlist[6:]))
f1.close()
f2.close()

I thought that if i could do the .strip() for chunks of f1 then i could append each to the external file, but couldn't work out how.

[bvdet]

Instead of reading the entire file into memory, iterate on the file object and incrementally write to the output file.

f1 = open("test1.txt")
f2 = open("test1_output.txt", "w")
for i, line in enumerate(f1):
    if i < 6:
        f2.write(line)
    else:
        f2.write(line.strip())
f1.close()
f2.close()

[Chris9]

Thanks very much Bvdet. I had to add a line after line 7:
f2.write(" ")