Getting Started


The following prerequisites are required by headlock and thus have to be installed before using it. Currently it is only explicitly tested with the minimal version requirements. Higher versions should work nevertheless.

  • Windows or Linux are required
  • CPython 3 Version 3.6 or higher is required
  • LLVM (Version 7.0.0 or higher).
  • GCC is required (in case of Windows MinGW64 is needed). Later other C compilers shall be supported!


The easiest way to install headlock is from PyPI via pip. To Install the most up-to-date stable release (0.5.0) run:

pip install headlock

Alternatively one can install the latest development branch directly from the github repository via

pip install git+


AVIRA and maybe also other virus scanners seems to delay loading DLLs compiled a moment ago by multiple seconds (see this link). As this feature is essential for headlock, you must add you project directory to the list of directories, that shall not be scanned by the realtime scanner. Otherwise the first instantiation of a testsetup will require 10-30 seconds per run.


The following sample demonstrates the basic features of headlock. That is automaticially compile and load a piece of C code (including mocking and prepocessor macros via command line) and calling it from python.

The following demo C code has 3 implementations for incrementing a given integer by the macro INCREMENT_OFFSET (has to be set via compiler command line):

int increment(int number)

    return number + INCREMENT_OFFSET;

void increment_inplace(int * number)
    *number += INCREMENT_OFFSET;

struct add_operands_t {
    int op1, op2;
extern int adder(struct add_operands_t * ops);

int increment_via_extfunc(int number)
    // adder_from_other_module() is not part of this file!
    struct add_operands_t ops = { number, INCREMENT_OFFSET);
    return external_adder(&ops);

Lets assume this code is stored in test.c and shall be tested from python. Then the following python file (in this case in the same directory) will call the increment*() functions and test if their result is correct:

from headlock.testsetup import TestSetup, CModule

@CModule('test.c', INCREMENT_OFFSET=1)
class TSSample(TestSetup):

ts = TSSample()

# test increment():
assert ts.increment(10) == 11

# test increment_inplace()
int_var =
assert int_var == 11

# test increment_via_extfunc()
ts.adder_mock = lambda ops: ops.op1 + ops.op2   # mock required func
assert ts.increment_via_extfunc(10) == 11

# this call is recommended (although it will be done implicitly otherwise)