A python package for changing the value of "2 + 2" (generally to equal "5") at runtime
Clone or download
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Permalink
Type Name Latest commit message Commit time
Failed to load latest commit information.
doublescript
.gitignore
.travis.yml
LICENSE
MANIFEST.in
README.rst
runtests.py
setup.cfg
setup.py
tox.ini

README.rst

python-doublescript

https://travis-ci.org/fdintino/python-doublescript.svg?branch=master

python-doublescript is a package that allows runtime manipulation of the evaluated value of “2 + 2” (generally to cause the result to equal “5”). The name of the package and the specific focus on “2 + 2 = 5” comes from the novel 1984 by George Orwell, but the motivation is to explore CPython internals and how one would go about monkey-patching those internals at runtime using ctypes.

This package was the subject of a talk at EuroPython 2017: 2 + 2 = 5: Monkey-patching CPython with ctypes to conform to Party doctrine (slides). The video will be posted when it is made available.

Usage

from doublescript import two_plus_two_equals

with two_plus_two_equals(5):
    print(eval("2 + 2"))  # prints "5"

Or, if you’re feeling adventurous (currently only works on x86 architectures):

export DOUBLEPLUSNOPYTHONOPT=1

python

In [1]: with two_plus_two_equals(5):
   ...:     print(2 + 2)
   ...:
5

Caveats

This implementation is CPython-specific, so it won’t work with other python interpreters (e.g., PyPy). Another thing to consider is that python folds binary operations when generating opcode as an optimization. What this means in practice is that an inline 2 + 2 (as opposed to eval("2 + 2")) will simply become 4 in the opcodes. This python behavior can be disabled by setting the environment variable DOUBLEPLUSNOPYTHONOPT before running your scripts. This applies equally to .pyc files: if the pyc files were generated with the normal python opcode optimizations, this library will have no effect on inline 2 + 2 expressions, since they will have already been turned into 4. At present, disabling opcode optimizations only works in x86 architectures.

Also, to state the obvious: don’t use this library in production.

License

Copyright (©) The Ministry of Truth, 1984. Licensed under the Simplified BSD License. View the LICENSE file under the root directory for complete license and copyright information.