What's the bad magic number error?

The magic number comes from UNIX-type systems where the first few bytes of a file held a marker indicating the file type.

Python puts a similar marker into its pyc files when it creates them.

Then the python interpreter makes sure this number is correct when loading it.

Anything that damages this magic number will cause your problem. This includes editing the pyc file or trying to run a pyc from a different version of python (usually later) than your interpreter.

If they are your pyc files, just delete them and let the interpreter re-compile the py files. On UNIX type systems, that could be something as simple as:

rm *.pyc

or:

find . -name '*.pyc' -delete

If they are not yours, you'll have to either get the py files for re-compilation, or an interpreter that can run the pyc files with that particular magic value.

One thing that might be causing the intermittent nature. The pyc that's causing the problem may only be imported under certain conditions. It's highly unlikely it would import sometimes. You should check the actual full stack trace when the import fails?

As an aside, the first word of all my 2.5.1(r251:54863) pyc files is 62131, 2.6.1(r261:67517) is 62161. The list of all magic numbers can be found in Python/import.c, reproduced here for completeness (current as at the time the answer was posted, it may have changed since then):

1.5:   20121
1.5.1: 20121
1.5.2: 20121
1.6:   50428
2.0:   50823
2.0.1: 50823
2.1:   60202
2.1.1: 60202
2.1.2: 60202
2.2:   60717
2.3a0: 62011
2.3a0: 62021
2.3a0: 62011
2.4a0: 62041
2.4a3: 62051
2.4b1: 62061
2.5a0: 62071
2.5a0: 62081
2.5a0: 62091
2.5a0: 62092
2.5b3: 62101
2.5b3: 62111
2.5c1: 62121
2.5c2: 62131
2.6a0: 62151
2.6a1: 62161
2.7a0: 62171

Loading a python3 generated *.pyc file with python2 also causes this error.

This can also be due to missing __init__.py file from the directory. Say if you create a new directory in Django for separating the unit tests into multiple files and place them in one directory then you also have to create the __init__.py file beside all the other files in new created test directory. otherwise it can give error like:

Traceback (most recent call last):
  File "C:\Users\USERNAME\AppData\Local\Programs\Python\Python35\Lib\unittest\loader.py",line 153, in loadTestsFromName
    module = __import__(module_name)
ImportError: bad magic number in 'APPNAME.tests': b'\x03\xf3\r\n'

"Bad magic number" error also happens if you have manually named your file with an extension .pyc

In my case, I've git clone a lib which had an interpreter of

#!/usr/bin/env python

While python was leading to Python2.7 even though my main code was running with python3.6 ... it still created a *.pyc file for 2.7 version ...

I can say that this error probably is a result of a mix between 2.7 & 3+ versions, this is why cleanup ( in any way you can think of that you're using ) - will help here ...

• don't forget to adjust those Python2x code -> python 3...

So I had the same error : ImportError bad magic number. This was on windows 10

This error was because I installed mysql-connector

So I had to:

pip uninstall mysql-comnector
pip uninstall mysql-connector-python
pip install mysql-connector-python

You will need to run this command in every path you have in your environment.

>>> import sys
>>> sys.path
['', '/usr/lib/python36.zip', '/usr/lib/python3.6', '/usr/lib/python3.6/lib-dynload', '/usr/local/lib/python3.6/dist-packages', '/source_code/src/python', '/usr/lib/python3/dist-packages']

Then run the command in every directory here

find /usr/lib/python3.6/ -name "*.pyc" -delete
find /usr/local/lib/python3.6/dist-packages -name "*.pyc" -delete
# etc...