4.5. Insight Into BCC Mode

BCC mode could convert most of functions and methods in the scripts to equivalent C functions, those c functions will be compiled to machine instructions directly, then called by obfuscated scripts.

It requires c compiler. In Linux and Darwin, gcc and clang is OK. In Windows, only clang.exe works. It could be configured by one of these ways:

  • If there is any clang.exe, it’s OK if it could be run in other path.

  • Download and install Windows version of LLVM

  • Download https://pyarmor.dashingsoft.com/downloads/tools/clang-9.0.zip, it’s about 26M bytes, there is only one file in it. Unzip it and save clang.exe to $HOME/.pyarmor/. $HOME is home path of current logon user, check the environment variable HOME to get the real path.

4.5.1. Enable BCC mode

After compiler works, using --enable-bcc to enable BCC mode:

$ pyarmor gen --enable-bcc foo.py

All the source in module level is not converted to C function.

4.5.2. Trace bcc log

To check which functions are converted to C function, enable trace mode before obfuscate the script:

$ pyarmor cfg enable_trace=1
$ pyarmor gen --enable-bcc foo.py

Then check the trace log:

$ ls .pyarmor/pyarmor.trace.log
$ grep trace.bcc .pyarmor/pyarmor.trace.log

trace.bcc            foo:5:hello
trace.bcc            foo:9:sum2
trace.bcc            foo:12:main

The first log means foo.py line 5 function hello is protected by bcc. The second log means foo.py line 9 function sum2 is protected by bcc.

If there is ! after trace.bcc, it means this function is ignored by BCC mode. For example:

trace.bcc ! foo:29:Test.new (unsupported function "super")

4.5.3. Ignore module or function

When BCC scripts reports errors, a quick workaround is to ignore these problem modules or functions. Because BCC mode converts some functions to C code, these functions are not compatible with Python function object. They may not be called by outer Python scripts, and can’t be fixed in Pyarmor side. In this case use configuration option bcc:excludes and bcc:disabled to ignore function or module, and make all the others work.

To ignore one module pkgname.modname by this command:

$ pyarmor cfg -p pkgname.modname bcc:disabled=1

To ignore functions or class methods in one module:

$ pyarmor cfg -p pkgname.modname bcc:excludes="name"
$ pyarmor cfg -p pkgname.modname bcc:excludes="name1 name2 name3"

$ pyarmor cfg -p pkgname.modname bcc:excludes="Class.method_1"
$ pyarmor cfg -p pkgname.modname bcc:excludes="Class.*"

If no option -p, same name function in the other scripts will be ignored too.

Here it’s an example script foo.py

def hello_a():

def hello_b():

class Test(object):

    def __init__(self):

    def hello_a():

Exclude functions by one of forms:

$ pyarmor cfg -p foo bcc:excludes = "hello_a"
$ pyarmor cfg -p foo bcc:excludes = "hello_a hello_b"
$ pyarmor cfg -p foo bcc:excludes = "hello_*"

$ pyarmor cfg -p foo bcc:excludes = "Test.hello_a"
$ pyarmor cfg -p foo bcc:excludes = "Test.*"
$ pyarmor cfg -p foo bcc:excludes = "Test.__*__"

$ pyarmor cfg -p foo bcc:excludes = "hello_a Test.hello_a"

If want to BCC mode handle specified functions, use option bcc:includes:

# clear excludes
$ pyarmor cfg bcc:excludes = ""

# BCC mode only handles module function "hello_a"
$ pyarmor cfg -p foo bcc:includes = "hello_a"

# Need extra settings let BCC mode handle class method "Test.hello_a"
$ pyarmor cfg -p foo bcc:includes + "Test.hello_a"

# BCC mode handles all methods of class "Test" except method "__init__"
$ pyarmor cfg -p foo bcc:includes="Test.*" bcc:excludes="Test.__init__"

Let’s enable trace mode to check these functions are ignored:

$ pyarmor cfg enable_trace 1
$ pyarmor gen --enable-bcc foo.py
$ grep trace.bcc .pyarmor/pyarmor.trace.log

Another example, in the following commands BCC mode ignores joker/card.py, but handle all the other scripts in package joker:

$ pyarmor cfg -p joker.card bcc:disabled=1
$ pyarmor gen --enable-bcc /path/to/pkg/joker

Both bcc:includes and bcc:excludes only work on top function and class method, they can’t be used to filter nest function and methods of nest class.

For example,

def hello():

    def wrap():

    class Test:

        def __init__(self):

The nest function wrap and nest class Test can’t be ignored by the following commands:

pyarmor cfg bcc:excludes = "wrap hello.wrap Test.__init__ hello.Test.__init__"

The only solution is to ignore top function hello:

pyarmor cfg bcc:excludes = hello

New in version 8.3.4: The option bcc:includes.

Changed in version 8.3.4: The option bcc:excludes, in previous version:

# Exclude module function "hello_a" and any method "hello_a"
pyarmor cfg bcc:excludes="hello_a"

# It doesn't work if there is class name in filter
pyarmor cfg bcc:excludes="Myclass.hello_a"


# Exclude module function "hello_a" and method "hello_a" in any class
pyarmor cfg bcc:excludes="hello_a *.hello_a"

# It works to ignore one method "Myclass.hello_a"
pyarmor cfg bcc:excludes="Myclass.hello_a"

4.5.4. Changed features

Here are some changed features in the BCC mode:

  • Calling raise without argument not in the exception handler will raise different exception.

>>> raise
RuntimeError: No active exception to re-raise

# In BCC mode
>>> raise
UnboundlocalError: local variable referenced before assignment
  • Some exception messages may different from the plain script.

  • Most of function attributes which starts with __ doesn’t exists, or the value is different from the original.

4.5.5. Unsupported features

If a function uses any unsupported features, it could not be converted into C code.

Here list unsupported features for BCC mode:

unsupport_nodes = (

    ast.AsyncFunctionDef, ast.AsyncFor, ast.AsyncWith,
    ast.Await, ast.Yield, ast.YieldFrom, ast.GeneratorExp,


    ast.MatchValue, ast.MatchSingleton, ast.MatchSequence,
    ast.MatchMapping, ast.MatchClass, ast.MatchStar,
    ast.MatchAs, ast.MatchOr

And unsupported functions:

  • exec

  • eval

  • super

  • locals

  • sys._getframe

  • sys.exc_info

For example, the following functions are not obfuscated by BCC mode, because they use unsupported features or unsupported functions:

async def nested():
    return 42

def foo1():
    for n range(10):
        yield n

def foo2():
   frame = sys._getframe(2)
   print('parent frame is', frame)

4.5.6. Known issues

  • When format string has syntax error, BCC mode may raise SystemError: NULL object passed to Py_BuildValue, instead of SyntaxError or ValueError.

    Found in test cases lib/python3.12/test/test_fstring.py: - test_invalid_syntax_error_message - test_missing_variable - test_syntax_error_for_starred_expressions - test_with_a_commas_and_an_underscore_in_format_specifier - test_with_an_underscore_and_a_comma_in_format_specifier - test_with_two_commas_in_format_specifier - test_with_two_underscore_in_format_specifier