Techniques for Protecting Python Source Code: .pyc Distribution, Obfuscation, py2exe, and Cython

Due to Python's dynamic nature and open‑source characteristics, protecting Python code is challenging, prompting the community to explore encryption, obfuscation, and packaging solutions.

1 Distribute .pyc Files

1.1 Idea

The Python interpreter compiles source to .pyc bytecode, which can be executed directly; the binary .pyc file is not human‑readable.

1.2 Method

Compile .py files to .pyc using the standard library compileall module:

<code>python -m compileall &lt;src&gt;</code>

Then remove the original .py files, e.g.:

<code>find &lt;src&gt; -name '*.py' -type f -print -exec rm {} \;</code>

1.3 Advantages

Simple, raises the barrier for casual source inspection.

Cross‑platform: .py runs anywhere, so the compiled .pyc does too.

1.4 Disadvantages

Bytecode is interpreter‑specific; compatibility issues may arise.

Decompilers (e.g., uncompyle6 ) can recover source relatively easily.

2 Code Obfuscation

2.1 Idea

Obfuscation makes code harder to understand by removing comments, altering indentation, renaming identifiers, inserting dead code, etc.

2.2 Methods

Method 1: Use the online tool oxyry to obfuscate Python code.

<code># coding: utf-8
class A(object):
    """ Description """
    def __init__(self, x, y, default=None):
        self.z = x + y
        self.default = default
    def name(self):
        return 'No Name'

def always():
    return True

num = 1
a = A(num, 999, 100)
a.name()
always()</code>

Obfuscated output (oxyry) mainly changes comments, parameter names and spacing.

Method 2: Use the pyobfuscate library.

<code># coding: utf-8
if 64 - 64: i11iIiiIiiif 65 - 65: O0 / iIii1I11I1II1 % OoooooooOO - i1IIcclass o0OO00 ( object ) :
  if 78 - 78: i11i . oOooOoO0Oo0O
  ... (truncated for brevity)</code>

2.3 Advantages

Simple, raises the difficulty of reverse engineering.

Good compatibility as long as logic remains unchanged.

2.4 Disadvantages

Works only on single files; multi‑module projects are not handled.

Structure remains unchanged; bytecode can still be extracted.

3 Using py2exe

3.1 Idea

py2exe packages Python scripts into Windows executables by bundling compiled .pyc files with required libraries.

3.2 Method

1) Create an entry script hello.py :

<code>print 'Hello World'</code>

2) Write setup.py :

<code>from distutils.core import setup
import py2exe
setup(console=['hello.py'])</code>

3) Build the executable:

<code>python setup.py py2exe</code>

The resulting file is dist\hello.exe .

3.3 Advantages

Produces a ready‑to‑run Windows executable, simplifying distribution.

Higher cracking barrier than plain .pyc .

3.4 Disadvantages

Windows‑only.

The executable still contains .pyc files that can be decompiled.

4 Using Cython

4.1 Idea

Cython compiles .py / .pyx to C source ( .c ) and then to shared libraries ( .so on Unix, .pyd on Windows), making reverse engineering harder while also improving performance.

4.2 Method

1) Write hello.pyx (or hello.py ) containing the Python code.

<code>def hello():
    print('hello')</code>

2) Create setup.py :

<code>from distutils.core import setup
from Cython.Build import cythonize
setup(name='Hello World app', ext_modules=cythonize('hello.pyx'))</code>

3) Build the extension:

<code>python setup.py build_ext --inplace</code>

4) Use the compiled module:

<code>python -c "from hello import hello; hello()"</code>

4.3 Advantages

Compiled binaries ( .so / .pyd ) are difficult to crack.

Provides performance gains.

4.4 Disadvantages

Compatibility varies across OS versions; recompilation may be needed.

Not all Python code is supported; fixing incompatibilities can be costly.

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