✏ EDIT: depends.py

import sys
import marshal
import contextlib
import dis
from distutils.version import StrictVersion

from ._imp import find_module, PY_COMPILED, PY_FROZEN, PY_SOURCE
from . import _imp

__all__ = [
    'Require', 'find_module', 'get_module_constant', 'extract_constant'
]

class Require:
    """A prerequisite to building or installing a distribution"""

def __init__(
            self, name, requested_version, module, homepage='',
            attribute=None, format=None):

if format is None and requested_version is not None:
            format = StrictVersion

if format is not None:
            requested_version = format(requested_version)
            if attribute is None:
                attribute = '__version__'

self.__dict__.update(locals())
        del self.self

def full_name(self):
        """Return full package/distribution name, w/version"""
        if self.requested_version is not None:
            return '%s-%s' % (self.name, self.requested_version)
        return self.name

def version_ok(self, version):
        """Is 'version' sufficiently up-to-date?"""
        return self.attribute is None or self.format is None or \
            str(version) != "unknown" and version >= self.requested_version

def get_version(self, paths=None, default="unknown"):
        """Get version number of installed module, 'None', or 'default'

Search 'paths' for module.  If not found, return 'None'.  If found,
        return the extracted version attribute, or 'default' if no version
        attribute was specified, or the value cannot be determined without
        importing the module.  The version is formatted according to the
        requirement's version format (if any), unless it is 'None' or the
        supplied 'default'.
        """

if self.attribute is None:
            try:
                f, p, i = find_module(self.module, paths)
                if f:
                    f.close()
                return default
            except ImportError:
                return None

v = get_module_constant(self.module, self.attribute, default, paths)

if v is not None and v is not default and self.format is not None:
            return self.format(v)

return v

def is_present(self, paths=None):
        """Return true if dependency is present on 'paths'"""
        return self.get_version(paths) is not None

def is_current(self, paths=None):
        """Return true if dependency is present and up-to-date on 'paths'"""
        version = self.get_version(paths)
        if version is None:
            return False
        return self.version_ok(version)

def maybe_close(f):
    @contextlib.contextmanager
    def empty():
        yield
        return
    if not f:
        return empty()

return contextlib.closing(f)

def get_module_constant(module, symbol, default=-1, paths=None):
    """Find 'module' by searching 'paths', and extract 'symbol'

Return 'None' if 'module' does not exist on 'paths', or it does not define
    'symbol'.  If the module defines 'symbol' as a constant, return the
    constant.  Otherwise, return 'default'."""

try:
        f, path, (suffix, mode, kind) = info = find_module(module, paths)
    except ImportError:
        # Module doesn't exist
        return None

with maybe_close(f):
        if kind == PY_COMPILED:
            f.read(8)  # skip magic & date
            code = marshal.load(f)
        elif kind == PY_FROZEN:
            code = _imp.get_frozen_object(module, paths)
        elif kind == PY_SOURCE:
            code = compile(f.read(), path, 'exec')
        else:
            # Not something we can parse; we'll have to import it.  :(
            imported = _imp.get_module(module, paths, info)
            return getattr(imported, symbol, None)

return extract_constant(code, symbol, default)

def extract_constant(code, symbol, default=-1):
    """Extract the constant value of 'symbol' from 'code'

If the name 'symbol' is bound to a constant value by the Python code
    object 'code', return that value.  If 'symbol' is bound to an expression,
    return 'default'.  Otherwise, return 'None'.

Return value is based on the first assignment to 'symbol'.  'symbol' must
    be a global, or at least a non-"fast" local in the code block.  That is,
    only 'STORE_NAME' and 'STORE_GLOBAL' opcodes are checked, and 'symbol'
    must be present in 'code.co_names'.
    """
    if symbol not in code.co_names:
        # name's not there, can't possibly be an assignment
        return None

name_idx = list(code.co_names).index(symbol)

STORE_NAME = 90
    STORE_GLOBAL = 97
    LOAD_CONST = 100

const = default

for byte_code in dis.Bytecode(code):
        op = byte_code.opcode
        arg = byte_code.arg

if op == LOAD_CONST:
            const = code.co_consts[arg]
        elif arg == name_idx and (op == STORE_NAME or op == STORE_GLOBAL):
            return const
        else:
            const = default

def _update_globals():
    """
    Patch the globals to remove the objects not available on some platforms.

XXX it'd be better to test assertions about bytecode instead.
    """

if not sys.platform.startswith('java') and sys.platform != 'cli':
        return
    incompatible = 'extract_constant', 'get_module_constant'
    for name in incompatible:
        del globals()[name]
        __all__.remove(name)

_update_globals()

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