Hack to get the uncompressed size of a gzip file without reading the whole thing.

main.py

#!/usr/bin/env python
"""
Test if we can reliably figure out the uncompressed size of .gz file...

"""
import gzip
import os
import subprocess


NUM_FILES = 10

# 1. Generate some sample text files.
files = []
for i in range(NUM_FILES):
    filename = f"data_{i}.txt"
    files.append(filename)

    data = ''
    for x in range(1000 * i):
        data += 'a'

    with open(filename, "w") as f:
        f.write(data)

    st = os.stat(filename)
    print(f"{filename} is {st.st_size} bytes uncompressed")


# 2. Use the OS's gzip command to compress the files.
for filename in files:
    subprocess.call(['gzip', filename])
print(f"Compressed {len(files)} files...")

# Rename our list of files...
files = [f'{file}.gz' for file in files]


# 3. Look at current file size, & report on uncompressed size
for filename in files:
    st = os.stat(filename)

    f = gzip.open(filename, 'rb')
    x = f.seek(0, 2)  # NOTE: Seek to the end of the file to get the uncompressed size
    print(f"{filename} is {st.st_size} bytes compressed, was {x} bytes uncompressed.")
    f.close()