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pythonstringfilecompressionzlib

Python wont save compressed string using zlib

According to this website and guide it should be pretty trivial to save the string as compressed using zlib.

import zlib

my_data = 'Hello world'

compressed_data = zlib.compress(my_data, 2)

f = open('outfile.txt', 'w')
f.write(compressed_data)
f.close()

This code should save "Hello world" into txt file as compressed. I'm getting these errors:

compressed_data = zlib.compress(my_data, 2)

TypeError: a bytes-like object is required, not 'str'

I have also tried adding this but then i get other error saying

new_data = zlib.compress(my_data.encode())
compressed_data = zlib.compress(new_data, 2)

And then i get errors like this:

TypeError: write() argument must be str, not bytes

I have also tried adding b' in front of the text in my_data but that gave me new error

my_data = b'Hello world'

TypeError: write() argument must be str, not bytes

Solution

  • The example you found deep in the bowels of the interwebs is for Python 2, not Python 3. Python 3 makes a distinction between strings of characters and strings of bytes. All is well with the addition of two "b"s:

    import zlib
my_data = b'Hello world'
compressed_data = zlib.compress(my_data, 2)
f = open('outfile.txt', 'wb')
f.write(compressed_data)
f.close()

    By the way, I have no idea why they wanted to use compression level 2. Just leave out the , 2. It will then use the default compression level, which is a good balance between time and compression ratio.