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import unittest
GLOBAL_VAR = None
class NamedExpressionInvalidTest(unittest.TestCase):
def test_named_expression_invalid_01(self):
code = """x := 0"""
with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
exec(code, {}, {})
def test_named_expression_invalid_02(self):
code = """x = y := 0"""
with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
exec(code, {}, {})
def test_named_expression_invalid_03(self):
code = """y := f(x)"""
with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
exec(code, {}, {})
def test_named_expression_invalid_04(self):
code = """y0 = y1 := f(x)"""
with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
exec(code, {}, {})
def test_named_expression_invalid_06(self):
code = """((a, b) := (1, 2))"""
with self.assertRaisesRegex(SyntaxError, "cannot use assignment expressions with tuple"):
exec(code, {}, {})
def test_named_expression_invalid_07(self):
code = """def spam(a = b := 42): pass"""
with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
exec(code, {}, {})
def test_named_expression_invalid_08(self):
code = """def spam(a: b := 42 = 5): pass"""
with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
exec(code, {}, {})
def test_named_expression_invalid_09(self):
code = """spam(a=b := 'c')"""
with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
exec(code, {}, {})
def test_named_expression_invalid_10(self):
code = """spam(x = y := f(x))"""
with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
exec(code, {}, {})
def test_named_expression_invalid_11(self):
code = """spam(a=1, b := 2)"""
with self.assertRaisesRegex(SyntaxError,
"positional argument follows keyword argument"):
exec(code, {}, {})
def test_named_expression_invalid_12(self):
code = """spam(a=1, (b := 2))"""
with self.assertRaisesRegex(SyntaxError,
"positional argument follows keyword argument"):
exec(code, {}, {})
def test_named_expression_invalid_13(self):
code = """spam(a=1, (b := 2))"""
with self.assertRaisesRegex(SyntaxError,
"positional argument follows keyword argument"):
exec(code, {}, {})
def test_named_expression_invalid_14(self):
code = """(x := lambda: y := 1)"""
with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
exec(code, {}, {})
def test_named_expression_invalid_15(self):
code = """(lambda: x := 1)"""
with self.assertRaisesRegex(SyntaxError,
"cannot use assignment expressions with lambda"):
exec(code, {}, {})
def test_named_expression_invalid_16(self):
code = "[i + 1 for i in i := [1,2]]"
with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
exec(code, {}, {})
def test_named_expression_invalid_17(self):
code = "[i := 0, j := 1 for i, j in [(1, 2), (3, 4)]]"
with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
exec(code, {}, {})
def test_named_expression_invalid_in_class_body(self):
code = """class Foo():
[(42, 1 + ((( j := i )))) for i in range(5)]
"""
with self.assertRaisesRegex(SyntaxError,
"assignment expression within a comprehension cannot be used in a class body"):
exec(code, {}, {})
def test_named_expression_invalid_rebinding_comprehension_iteration_variable(self):
cases = [
("Local reuse", 'i', "[i := 0 for i in range(5)]"),
("Nested reuse", 'j', "[[(j := 0) for i in range(5)] for j in range(5)]"),
("Reuse inner loop target", 'j', "[(j := 0) for i in range(5) for j in range(5)]"),
("Unpacking reuse", 'i', "[i := 0 for i, j in [(0, 1)]]"),
("Reuse in loop condition", 'i', "[i+1 for i in range(5) if (i := 0)]"),
("Unreachable reuse", 'i', "[False or (i:=0) for i in range(5)]"),
("Unreachable nested reuse", 'i',
"[(i, j) for i in range(5) for j in range(5) if True or (i:=10)]"),
]
for case, target, code in cases:
msg = f"assignment expression cannot rebind comprehension iteration variable '{target}'"
with self.subTest(case=case):
with self.assertRaisesRegex(SyntaxError, msg):
exec(code, {}, {})
def test_named_expression_invalid_rebinding_comprehension_inner_loop(self):
cases = [
("Inner reuse", 'j', "[i for i in range(5) if (j := 0) for j in range(5)]"),
("Inner unpacking reuse", 'j', "[i for i in range(5) if (j := 0) for j, k in [(0, 1)]]"),
]
for case, target, code in cases:
msg = f"comprehension inner loop cannot rebind assignment expression target '{target}'"
with self.subTest(case=case):
with self.assertRaisesRegex(SyntaxError, msg):
exec(code, {}) # Module scope
with self.assertRaisesRegex(SyntaxError, msg):
exec(code, {}, {}) # Class scope
with self.assertRaisesRegex(SyntaxError, msg):
exec(f"lambda: {code}", {}) # Function scope
def test_named_expression_invalid_comprehension_iterable_expression(self):
cases = [
("Top level", "[i for i in (i := range(5))]"),
("Inside tuple", "[i for i in (2, 3, i := range(5))]"),
("Inside list", "[i for i in [2, 3, i := range(5)]]"),
("Different name", "[i for i in (j := range(5))]"),
("Lambda expression", "[i for i in (lambda:(j := range(5)))()]"),
("Inner loop", "[i for i in range(5) for j in (i := range(5))]"),
("Nested comprehension", "[i for i in [j for j in (k := range(5))]]"),
("Nested comprehension condition", "[i for i in [j for j in range(5) if (j := True)]]"),
("Nested comprehension body", "[i for i in [(j := True) for j in range(5)]]"),
]
msg = "assignment expression cannot be used in a comprehension iterable expression"
for case, code in cases:
with self.subTest(case=case):
with self.assertRaisesRegex(SyntaxError, msg):
exec(code, {}) # Module scope
with self.assertRaisesRegex(SyntaxError, msg):
exec(code, {}, {}) # Class scope
with self.assertRaisesRegex(SyntaxError, msg):
exec(f"lambda: {code}", {}) # Function scope
class NamedExpressionAssignmentTest(unittest.TestCase):
def test_named_expression_assignment_01(self):
(a := 10)
self.assertEqual(a, 10)
def test_named_expression_assignment_02(self):
a = 20
(a := a)
self.assertEqual(a, 20)
def test_named_expression_assignment_03(self):
(total := 1 + 2)
self.assertEqual(total, 3)
def test_named_expression_assignment_04(self):
(info := (1, 2, 3))
self.assertEqual(info, (1, 2, 3))
def test_named_expression_assignment_05(self):
(x := 1, 2)
self.assertEqual(x, 1)
def test_named_expression_assignment_06(self):
(z := (y := (x := 0)))
self.assertEqual(x, 0)
self.assertEqual(y, 0)
self.assertEqual(z, 0)
def test_named_expression_assignment_07(self):
(loc := (1, 2))
self.assertEqual(loc, (1, 2))
def test_named_expression_assignment_08(self):
if spam := "eggs":
self.assertEqual(spam, "eggs")
else: self.fail("variable was not assigned using named expression")
def test_named_expression_assignment_09(self):
if True and (spam := True):
self.assertTrue(spam)
else: self.fail("variable was not assigned using named expression")
def test_named_expression_assignment_10(self):
if (match := 10) == 10:
pass
else: self.fail("variable was not assigned using named expression")
def test_named_expression_assignment_11(self):
def spam(a):
return a
input_data = [1, 2, 3]
res = [(x, y, x/y) for x in input_data if (y := spam(x)) > 0]
self.assertEqual(res, [(1, 1, 1.0), (2, 2, 1.0), (3, 3, 1.0)])
def test_named_expression_assignment_12(self):
def spam(a):
return a
res = [[y := spam(x), x/y] for x in range(1, 5)]
self.assertEqual(res, [[1, 1.0], [2, 1.0], [3, 1.0], [4, 1.0]])
def test_named_expression_assignment_13(self):
length = len(lines := [1, 2])
self.assertEqual(length, 2)
self.assertEqual(lines, [1,2])
def test_named_expression_assignment_14(self):
"""
Where all variables are positive integers, and a is at least as large
as the n'th root of x, this algorithm returns the floor of the n'th
root of x (and roughly doubling the number of accurate bits per
iteration):
"""
a = 9
n = 2
x = 3
while a > (d := x // a**(n-1)):
a = ((n-1)*a + d) // n
self.assertEqual(a, 1)
def test_named_expression_assignment_15(self):
while a := False:
pass # This will not run
self.assertEqual(a, False)
def test_named_expression_assignment_16(self):
a, b = 1, 2
fib = {(c := a): (a := b) + (b := a + c) - b for __ in range(6)}
self.assertEqual(fib, {1: 2, 2: 3, 3: 5, 5: 8, 8: 13, 13: 21})
def test_named_expression_assignment_17(self):
a = [1]
element = a[b:=0]
self.assertEqual(b, 0)
self.assertEqual(element, a[0])
def test_named_expression_assignment_18(self):
class TwoDimensionalList:
def __init__(self, two_dimensional_list):
self.two_dimensional_list = two_dimensional_list
def __getitem__(self, index):
return self.two_dimensional_list[index[0]][index[1]]
a = TwoDimensionalList([[1], [2]])
element = a[b:=0, c:=0]
self.assertEqual(b, 0)
self.assertEqual(c, 0)
self.assertEqual(element, a.two_dimensional_list[b][c])
class NamedExpressionScopeTest(unittest.TestCase):
def test_named_expression_scope_01(self):
code = """def spam():
(a := 5)
print(a)"""
with self.assertRaisesRegex(NameError, "name 'a' is not defined"):
exec(code, {}, {})
def test_named_expression_scope_02(self):
total = 0
partial_sums = [total := total + v for v in range(5)]
self.assertEqual(partial_sums, [0, 1, 3, 6, 10])
self.assertEqual(total, 10)
def test_named_expression_scope_03(self):
containsOne = any((lastNum := num) == 1 for num in [1, 2, 3])
self.assertTrue(containsOne)
self.assertEqual(lastNum, 1)
def test_named_expression_scope_04(self):
def spam(a):
return a
res = [[y := spam(x), x/y] for x in range(1, 5)]
self.assertEqual(y, 4)
def test_named_expression_scope_05(self):
def spam(a):
return a
input_data = [1, 2, 3]
res = [(x, y, x/y) for x in input_data if (y := spam(x)) > 0]
self.assertEqual(res, [(1, 1, 1.0), (2, 2, 1.0), (3, 3, 1.0)])
self.assertEqual(y, 3)
def test_named_expression_scope_06(self):
res = [[spam := i for i in range(3)] for j in range(2)]
self.assertEqual(res, [[0, 1, 2], [0, 1, 2]])
self.assertEqual(spam, 2)
def test_named_expression_scope_07(self):
len(lines := [1, 2])
self.assertEqual(lines, [1, 2])
def test_named_expression_scope_08(self):
def spam(a):
return a
def eggs(b):
return b * 2
res = [spam(a := eggs(b := h)) for h in range(2)]
self.assertEqual(res, [0, 2])
self.assertEqual(a, 2)
self.assertEqual(b, 1)
def test_named_expression_scope_09(self):
def spam(a):
return a
def eggs(b):
return b * 2
res = [spam(a := eggs(a := h)) for h in range(2)]
self.assertEqual(res, [0, 2])
self.assertEqual(a, 2)
def test_named_expression_scope_10(self):
res = [b := [a := 1 for i in range(2)] for j in range(2)]
self.assertEqual(res, [[1, 1], [1, 1]])
self.assertEqual(a, 1)
self.assertEqual(b, [1, 1])
def test_named_expression_scope_11(self):
res = [j := i for i in range(5)]
self.assertEqual(res, [0, 1, 2, 3, 4])
self.assertEqual(j, 4)
def test_named_expression_scope_17(self):
b = 0
res = [b := i + b for i in range(5)]
self.assertEqual(res, [0, 1, 3, 6, 10])
self.assertEqual(b, 10)
def test_named_expression_scope_18(self):
def spam(a):
return a
res = spam(b := 2)
self.assertEqual(res, 2)
self.assertEqual(b, 2)
def test_named_expression_scope_19(self):
def spam(a):
return a
res = spam((b := 2))
self.assertEqual(res, 2)
self.assertEqual(b, 2)
def test_named_expression_scope_20(self):
def spam(a):
return a
res = spam(a=(b := 2))
self.assertEqual(res, 2)
self.assertEqual(b, 2)
def test_named_expression_scope_21(self):
def spam(a, b):
return a + b
res = spam(c := 2, b=1)
self.assertEqual(res, 3)
self.assertEqual(c, 2)
def test_named_expression_scope_22(self):
def spam(a, b):
return a + b
res = spam((c := 2), b=1)
self.assertEqual(res, 3)
self.assertEqual(c, 2)
def test_named_expression_scope_23(self):
def spam(a, b):
return a + b
res = spam(b=(c := 2), a=1)
self.assertEqual(res, 3)
self.assertEqual(c, 2)
def test_named_expression_scope_24(self):
a = 10
def spam():
nonlocal a
(a := 20)
spam()
self.assertEqual(a, 20)
def test_named_expression_scope_25(self):
ns = {}
code = """a = 10
def spam():
global a
(a := 20)
spam()"""
exec(code, ns, {})
self.assertEqual(ns["a"], 20)
def test_named_expression_variable_reuse_in_comprehensions(self):
# The compiler is expected to raise syntax error for comprehension
# iteration variables, but should be fine with rebinding of other
# names (e.g. globals, nonlocals, other assignment expressions)
# The cases are all defined to produce the same expected result
# Each comprehension is checked at both function scope and module scope
rebinding = "[x := i for i in range(3) if (x := i) or not x]"
filter_ref = "[x := i for i in range(3) if x or not x]"
body_ref = "[x for i in range(3) if (x := i) or not x]"
nested_ref = "[j for i in range(3) if x or not x for j in range(3) if (x := i)][:-3]"
cases = [
("Rebind global", f"x = 1; result = {rebinding}"),
("Rebind nonlocal", f"result, x = (lambda x=1: ({rebinding}, x))()"),
("Filter global", f"x = 1; result = {filter_ref}"),
("Filter nonlocal", f"result, x = (lambda x=1: ({filter_ref}, x))()"),
("Body global", f"x = 1; result = {body_ref}"),
("Body nonlocal", f"result, x = (lambda x=1: ({body_ref}, x))()"),
("Nested global", f"x = 1; result = {nested_ref}"),
("Nested nonlocal", f"result, x = (lambda x=1: ({nested_ref}, x))()"),
]
for case, code in cases:
with self.subTest(case=case):
ns = {}
exec(code, ns)
self.assertEqual(ns["x"], 2)
self.assertEqual(ns["result"], [0, 1, 2])
def test_named_expression_global_scope(self):
sentinel = object()
global GLOBAL_VAR
def f():
global GLOBAL_VAR
[GLOBAL_VAR := sentinel for _ in range(1)]
self.assertEqual(GLOBAL_VAR, sentinel)
try:
f()
self.assertEqual(GLOBAL_VAR, sentinel)
finally:
GLOBAL_VAR = None
def test_named_expression_global_scope_no_global_keyword(self):
sentinel = object()
def f():
GLOBAL_VAR = None
[GLOBAL_VAR := sentinel for _ in range(1)]
self.assertEqual(GLOBAL_VAR, sentinel)
f()
self.assertEqual(GLOBAL_VAR, None)
def test_named_expression_nonlocal_scope(self):
sentinel = object()
def f():
nonlocal_var = None
def g():
nonlocal nonlocal_var
[nonlocal_var := sentinel for _ in range(1)]
g()
self.assertEqual(nonlocal_var, sentinel)
f()
def test_named_expression_nonlocal_scope_no_nonlocal_keyword(self):
sentinel = object()
def f():
nonlocal_var = None
def g():
[nonlocal_var := sentinel for _ in range(1)]
g()
self.assertEqual(nonlocal_var, None)
f()
if __name__ == "__main__":
unittest.main()