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.
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
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.
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.