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Filename :
_compat.py
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from __future__ import absolute_import, division, print_function import platform import sys import types import warnings PY2 = sys.version_info[0] == 2 PYPY = platform.python_implementation() == "PyPy" if PYPY or sys.version_info[:2] >= (3, 6): ordered_dict = dict else: from collections import OrderedDict ordered_dict = OrderedDict if PY2: from UserDict import IterableUserDict from collections import Mapping, Sequence # We 'bundle' isclass instead of using inspect as importing inspect is # fairly expensive (order of 10-15 ms for a modern machine in 2016) def isclass(klass): return isinstance(klass, (type, types.ClassType)) # TYPE is used in exceptions, repr(int) is different on Python 2 and 3. TYPE = "type" def iteritems(d): return d.iteritems() # Python 2 is bereft of a read-only dict proxy, so we make one! class ReadOnlyDict(IterableUserDict): """ Best-effort read-only dict wrapper. """ def __setitem__(self, key, val): # We gently pretend we're a Python 3 mappingproxy. raise TypeError( "'mappingproxy' object does not support item assignment" ) def update(self, _): # We gently pretend we're a Python 3 mappingproxy. raise AttributeError( "'mappingproxy' object has no attribute 'update'" ) def __delitem__(self, _): # We gently pretend we're a Python 3 mappingproxy. raise TypeError( "'mappingproxy' object does not support item deletion" ) def clear(self): # We gently pretend we're a Python 3 mappingproxy. raise AttributeError( "'mappingproxy' object has no attribute 'clear'" ) def pop(self, key, default=None): # We gently pretend we're a Python 3 mappingproxy. raise AttributeError( "'mappingproxy' object has no attribute 'pop'" ) def popitem(self): # We gently pretend we're a Python 3 mappingproxy. raise AttributeError( "'mappingproxy' object has no attribute 'popitem'" ) def setdefault(self, key, default=None): # We gently pretend we're a Python 3 mappingproxy. raise AttributeError( "'mappingproxy' object has no attribute 'setdefault'" ) def __repr__(self): # Override to be identical to the Python 3 version. return "mappingproxy(" + repr(self.data) + ")" def metadata_proxy(d): res = ReadOnlyDict() res.data.update(d) # We blocked update, so we have to do it like this. return res def just_warn(*args, **kw): # pragma: nocover """ We only warn on Python 3 because we are not aware of any concrete consequences of not setting the cell on Python 2. """ else: # Python 3 and later. from collections.abc import Mapping, Sequence # noqa def just_warn(*args, **kw): """ We only warn on Python 3 because we are not aware of any concrete consequences of not setting the cell on Python 2. """ warnings.warn( "Running interpreter doesn't sufficiently support code object " "introspection. Some features like bare super() or accessing " "__class__ will not work with slotted classes.", RuntimeWarning, stacklevel=2, ) def isclass(klass): return isinstance(klass, type) TYPE = "class" def iteritems(d): return d.items() def metadata_proxy(d): return types.MappingProxyType(dict(d)) def make_set_closure_cell(): """Return a function of two arguments (cell, value) which sets the value stored in the closure cell `cell` to `value`. """ # pypy makes this easy. (It also supports the logic below, but # why not do the easy/fast thing?) if PYPY: # pragma: no cover def set_closure_cell(cell, value): cell.__setstate__((value,)) return set_closure_cell # Otherwise gotta do it the hard way. # Create a function that will set its first cellvar to `value`. def set_first_cellvar_to(value): x = value return # This function will be eliminated as dead code, but # not before its reference to `x` forces `x` to be # represented as a closure cell rather than a local. def force_x_to_be_a_cell(): # pragma: no cover return x try: # Extract the code object and make sure our assumptions about # the closure behavior are correct. if PY2: co = set_first_cellvar_to.func_code else: co = set_first_cellvar_to.__code__ if co.co_cellvars != ("x",) or co.co_freevars != (): raise AssertionError # pragma: no cover # Convert this code object to a code object that sets the # function's first _freevar_ (not cellvar) to the argument. if sys.version_info >= (3, 8): # CPython 3.8+ has an incompatible CodeType signature # (added a posonlyargcount argument) but also added # CodeType.replace() to do this without counting parameters. set_first_freevar_code = co.replace( co_cellvars=co.co_freevars, co_freevars=co.co_cellvars ) else: args = [co.co_argcount] if not PY2: args.append(co.co_kwonlyargcount) args.extend( [ co.co_nlocals, co.co_stacksize, co.co_flags, co.co_code, co.co_consts, co.co_names, co.co_varnames, co.co_filename, co.co_name, co.co_firstlineno, co.co_lnotab, # These two arguments are reversed: co.co_cellvars, co.co_freevars, ] ) set_first_freevar_code = types.CodeType(*args) def set_closure_cell(cell, value): # Create a function using the set_first_freevar_code, # whose first closure cell is `cell`. Calling it will # change the value of that cell. setter = types.FunctionType( set_first_freevar_code, {}, "setter", (), (cell,) ) # And call it to set the cell. setter(value) # Make sure it works on this interpreter: def make_func_with_cell(): x = None def func(): return x # pragma: no cover return func if PY2: cell = make_func_with_cell().func_closure[0] else: cell = make_func_with_cell().__closure__[0] set_closure_cell(cell, 100) if cell.cell_contents != 100: raise AssertionError # pragma: no cover except Exception: return just_warn else: return set_closure_cell set_closure_cell = make_set_closure_cell()