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# Test the most dynamic corner cases of Python's runtime semantics.
import builtins
import contextlib
import unittest
from test.support import swap_item, swap_attr
class RebindBuiltinsTests(unittest.TestCase):
"""Test all the ways that we can change/shadow globals/builtins."""
def configure_func(self, func, *args):
"""Perform TestCase-specific configuration on a function before testing.
By default, this does nothing. Example usage: spinning a function so
that a JIT will optimize it. Subclasses should override this as needed.
Args:
func: function to configure.
*args: any arguments that should be passed to func, if calling it.
Returns:
Nothing. Work will be performed on func in-place.
"""
pass
def test_globals_shadow_builtins(self):
# Modify globals() to shadow an entry in builtins.
def foo():
return len([1, 2, 3])
self.configure_func(foo)
self.assertEqual(foo(), 3)
with swap_item(globals(), "len", lambda x: 7):
self.assertEqual(foo(), 7)
def test_modify_builtins(self):
# Modify the builtins module directly.
def foo():
return len([1, 2, 3])
self.configure_func(foo)
self.assertEqual(foo(), 3)
with swap_attr(builtins, "len", lambda x: 7):
self.assertEqual(foo(), 7)
def test_modify_builtins_while_generator_active(self):
# Modify the builtins out from under a live generator.
def foo():
x = range(3)
yield len(x)
yield len(x)
self.configure_func(foo)
g = foo()
self.assertEqual(next(g), 3)
with swap_attr(builtins, "len", lambda x: 7):
self.assertEqual(next(g), 7)
def test_modify_builtins_from_leaf_function(self):
# Verify that modifications made by leaf functions percolate up the
# callstack.
with swap_attr(builtins, "len", len):
def bar():
builtins.len = lambda x: 4
def foo(modifier):
l = []
l.append(len(range(7)))
modifier()
l.append(len(range(7)))
return l
self.configure_func(foo, lambda: None)
self.assertEqual(foo(bar), [7, 4])
def test_cannot_change_globals_or_builtins_with_eval(self):
def foo():
return len([1, 2, 3])
self.configure_func(foo)
# Note that this *doesn't* change the definition of len() seen by foo().
builtins_dict = {"len": lambda x: 7}
globals_dict = {"foo": foo, "__builtins__": builtins_dict,
"len": lambda x: 8}
self.assertEqual(eval("foo()", globals_dict), 3)
self.assertEqual(eval("foo()", {"foo": foo}), 3)
def test_cannot_change_globals_or_builtins_with_exec(self):
def foo():
return len([1, 2, 3])
self.configure_func(foo)
globals_dict = {"foo": foo}
exec("x = foo()", globals_dict)
self.assertEqual(globals_dict["x"], 3)
# Note that this *doesn't* change the definition of len() seen by foo().
builtins_dict = {"len": lambda x: 7}
globals_dict = {"foo": foo, "__builtins__": builtins_dict,
"len": lambda x: 8}
exec("x = foo()", globals_dict)
self.assertEqual(globals_dict["x"], 3)
def test_cannot_replace_builtins_dict_while_active(self):
def foo():
x = range(3)
yield len(x)
yield len(x)
self.configure_func(foo)
g = foo()
self.assertEqual(next(g), 3)
with swap_item(globals(), "__builtins__", {"len": lambda x: 7}):
self.assertEqual(next(g), 3)
def test_cannot_replace_builtins_dict_between_calls(self):
def foo():
return len([1, 2, 3])
self.configure_func(foo)
self.assertEqual(foo(), 3)
with swap_item(globals(), "__builtins__", {"len": lambda x: 7}):
self.assertEqual(foo(), 3)
def test_eval_gives_lambda_custom_globals(self):
globals_dict = {"len": lambda x: 7}
foo = eval("lambda: len([])", globals_dict)
self.configure_func(foo)
self.assertEqual(foo(), 7)
if __name__ == "__main__":
unittest.main()
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