EC
zipfile.BadZipFile
PythonERRORCommonI/O

ZIP file is corrupt or not a valid ZIP

Quick Answer

Catch zipfile.BadZipFile when opening untrusted or downloaded ZIP files; validate the file size and check the magic bytes before opening.

Production Risk

Medium — ZIP extraction from user uploads requires BadZipFile handling.

What this means

Raised by zipfile.ZipFile() when the file is not a valid ZIP archive — corrupted download, truncated file, or wrong file type.

Why it happens
  1. 1Download was interrupted leaving a truncated file
  2. 2File is not a ZIP — wrong Content-Type from server
  3. 3ZIP file was corrupted in transit or storage

Fix

Validate before opening

Validate before opening
import zipfile
import os

def safe_open_zip(path):
    if not os.path.exists(path) or os.path.getsize(path) == 0:
        raise ValueError(f"File missing or empty: {path}")
    try:
        return zipfile.ZipFile(path)
    except zipfile.BadZipFile as e:
        raise ValueError(f"Not a valid ZIP archive: {path}") from e

Why this works

Checking file size before opening catches empty downloads; the try/except wraps the BadZipFile into a domain error with the path.

Code examples
Triggerpython
import zipfile
zipfile.ZipFile('not_a_zip.txt')  # BadZipFile: File is not a zip file
Test with is_zipfilepython
if not zipfile.is_zipfile(path):
    raise ValueError(f"Not a ZIP: {path}")
with zipfile.ZipFile(path) as zf:
    zf.extractall(dest)
Same error in other languages
ZipExceptionin Java→
Sources
Official documentation ↗

Python Docs — zipfile module

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