17 # Rules for how modules can be loaded. Values are:

    21 modulepolicy = policy.policy

    18 #

    19 #    c - require C extensions

    20 #    allow - allow pure Python implementation when C loading fails

    21 #    py - only load pure Python modules

    22 #

    23 # By default, require the C extensions for performance reasons.

    24 modulepolicy = 'c'

    25 try:

    26     from . import __modulepolicy__

    27     modulepolicy = __modulepolicy__.modulepolicy

    28 except ImportError:

    29     pass

    30 

    31 # PyPy doesn't load C extensions.

    32 #

    33 # The canonical way to do this is to test platform.python_implementation().

    34 # But we don't import platform and don't bloat for it here.

    35 if '__pypy__' in sys.builtin_module_names:

    36     modulepolicy = 'py'

    37 

    38 # Our C extensions aren't yet compatible with Python 3. So use pure Python

    39 # on Python 3 for now.

    40 if sys.version_info[0] >= 3:

    41     modulepolicy = 'py'

    42 

    43 # Environment variable can always force settings.

    44 modulepolicy = os.environ.get('HGMODULEPOLICY', modulepolicy)