RustPython · youknowone · May 16, 2026 · May 16, 2026 · May 16, 2026
diff --git a/Lib/test/test_genexps.py b/Lib/test/test_genexps.py
@@ -0,0 +1,294 @@
+import sys
+import doctest
+import unittest
+
+
+doctests = """
+
+Test simple loop with conditional
+
+    >>> sum(i*i for i in range(100) if i&1 == 1)
+    166650
+
+Test simple nesting
+
+    >>> list((i,j) for i in range(3) for j in range(4) )
+    [(0, 0), (0, 1), (0, 2), (0, 3), (1, 0), (1, 1), (1, 2), (1, 3), (2, 0), (2, 1), (2, 2), (2, 3)]
+
+Test nesting with the inner expression dependent on the outer
+
+    >>> list((i,j) for i in range(4) for j in range(i) )
+    [(1, 0), (2, 0), (2, 1), (3, 0), (3, 1), (3, 2)]
+
+Test the idiom for temporary variable assignment in comprehensions.
+
+    >>> list((j*j for i in range(4) for j in [i+1]))
+    [1, 4, 9, 16]
+    >>> list((j*k for i in range(4) for j in [i+1] for k in [j+1]))
+    [2, 6, 12, 20]
+    >>> list((j*k for i in range(4) for j, k in [(i+1, i+2)]))
+    [2, 6, 12, 20]
+
+Not assignment
+
+    >>> list((i*i for i in [*range(4)]))
+    [0, 1, 4, 9]
+    >>> list((i*i for i in (*range(4),)))
+    [0, 1, 4, 9]
+
+Make sure the induction variable is not exposed
+
+    >>> i = 20
+    >>> sum(i*i for i in range(100))
+    328350
+    >>> i
+    20
+
+Test first class
+
+    >>> g = (i*i for i in range(4))
+    >>> type(g)
+    <class 'generator'>
+    >>> list(g)
+    [0, 1, 4, 9]
+
+Test direct calls to next()
+
+    >>> g = (i*i for i in range(3))
+    >>> next(g)
+    0
+    >>> next(g)
+    1
+    >>> next(g)
+    4
+    >>> next(g)
+    Traceback (most recent call last):
+      File "<pyshell#21>", line 1, in -toplevel-
+        next(g)
+    StopIteration
+
+Does it stay stopped?
+
+    >>> next(g)
+    Traceback (most recent call last):
+      File "<pyshell#21>", line 1, in -toplevel-
+        next(g)
+    StopIteration
+    >>> list(g)
+    []
+
+Test running gen when defining function is out of scope
+
+    >>> def f(n):
+    ...     return (i*i for i in range(n))
+    >>> list(f(10))
+    [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
+
+    >>> def f(n):
+    ...     return ((i,j) for i in range(3) for j in range(n))
+    >>> list(f(4))
+    [(0, 0), (0, 1), (0, 2), (0, 3), (1, 0), (1, 1), (1, 2), (1, 3), (2, 0), (2, 1), (2, 2), (2, 3)]
+    >>> def f(n):
+    ...     return ((i,j) for i in range(3) for j in range(4) if j in range(n))
+    >>> list(f(4))
+    [(0, 0), (0, 1), (0, 2), (0, 3), (1, 0), (1, 1), (1, 2), (1, 3), (2, 0), (2, 1), (2, 2), (2, 3)]
+    >>> list(f(2))
+    [(0, 0), (0, 1), (1, 0), (1, 1), (2, 0), (2, 1)]
+
+Verify that parenthesis are required in a statement
+
+    >>> def f(n):
+    ...     return i*i for i in range(n)
+    Traceback (most recent call last):
+       ...
+    SyntaxError: invalid syntax
+
+Verify that parenthesis are required when used as a keyword argument value
+
+    >>> dict(a = i for i in range(10))  # TODO: RUSTPYTHON # doctest: +EXPECTED_FAILURE
+    Traceback (most recent call last):
+       ...
+    SyntaxError: invalid syntax. Maybe you meant '==' or ':=' instead of '='?
+
+Verify that parenthesis are required when used as a keyword argument value
+
+    >>> dict(a = (i for i in range(10))) #doctest: +ELLIPSIS
+    {'a': <generator object <genexpr> at ...>}
+
+Verify early binding for the outermost for-expression
+
+    >>> x=10
+    >>> g = (i*i for i in range(x))
+    >>> x = 5
+    >>> list(g)
+    [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
+
+Verify late binding for the outermost if-expression
+
+    >>> include = (2,4,6,8)
+    >>> g = (i*i for i in range(10) if i in include)
+    >>> include = (1,3,5,7,9)
+    >>> list(g)
+    [1, 9, 25, 49, 81]
+
+Verify that the outermost for-expression makes an immediate check
+for iterability
+    >>> (i for i in 6)
+    Traceback (most recent call last):
+      File "<pyshell#4>", line 1, in -toplevel-
+        (i for i in 6)
+    TypeError: 'int' object is not iterable
+
+Verify late binding for the innermost for-expression
+
+    >>> g = ((i,j) for i in range(3) for j in range(x))
+    >>> x = 4
+    >>> list(g)
+    [(0, 0), (0, 1), (0, 2), (0, 3), (1, 0), (1, 1), (1, 2), (1, 3), (2, 0), (2, 1), (2, 2), (2, 3)]
+
+Verify re-use of tuples (a side benefit of using genexps over listcomps)
+
+    >>> tupleids = list(map(id, ((i,i) for i in range(10))))
+    >>> int(max(tupleids) - min(tupleids))
+    0
+
+Verify that syntax error's are raised for genexps used as lvalues
+
+    >>> (y for y in (1,2)) = 10  # TODO: RUSTPYTHON # doctest: +EXPECTED_FAILURE
+    Traceback (most recent call last):
+       ...
+    SyntaxError: cannot assign to generator expression
+
+    >>> (y for y in (1,2)) += 10  # TODO: RUSTPYTHON # doctest: +EXPECTED_FAILURE
+    Traceback (most recent call last):
+       ...
+    SyntaxError: 'generator expression' is an illegal expression for augmented assignment
+
+
+########### Tests borrowed from or inspired by test_generators.py ############
+
+Make a generator that acts like range()
+
+    >>> yrange = lambda n:  (i for i in range(n))
+    >>> list(yrange(10))
+    [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+
+Generators always return to the most recent caller:
+
+    >>> def creator():
+    ...     r = yrange(5)
+    ...     print("creator", next(r))
+    ...     return r
+    >>> def caller():
+    ...     r = creator()
+    ...     for i in r:
+    ...             print("caller", i)
+    >>> caller()
+    creator 0
+    caller 1
+    caller 2
+    caller 3
+    caller 4
+
+Generators can call other generators:
+
+    >>> def zrange(n):
+    ...     for i in yrange(n):
+    ...         yield i
+    >>> list(zrange(5))
+    [0, 1, 2, 3, 4]
+
+
+Verify that a gen exp cannot be resumed while it is actively running:
+
+    >>> g = (next(me) for i in range(10))
+    >>> me = g
+    >>> next(me)
+    Traceback (most recent call last):
+      File "<pyshell#30>", line 1, in -toplevel-
+        next(me)
+      File "<pyshell#28>", line 1, in <generator expression>
+        g = (next(me) for i in range(10))
+    ValueError: generator already executing
+
+Verify exception propagation
+
+    >>> g = (10 // i for i in (5, 0, 2))
+    >>> next(g)
+    2
+    >>> next(g)
+    Traceback (most recent call last):
+      File "<pyshell#37>", line 1, in -toplevel-
+        next(g)
+      File "<pyshell#35>", line 1, in <generator expression>
+        g = (10 // i for i in (5, 0, 2))
+    ZeroDivisionError: division by zero
+    >>> next(g)
+    Traceback (most recent call last):
+      File "<pyshell#38>", line 1, in -toplevel-
+        next(g)
+    StopIteration
+
+Make sure that None is a valid return value
+
+    >>> list(None for i in range(10))
+    [None, None, None, None, None, None, None, None, None, None]
+
+Check that generator attributes are present
+
+    >>> g = (i*i for i in range(3))
+    >>> expected = set(['gi_frame', 'gi_running'])
+    >>> set(attr for attr in dir(g) if not attr.startswith('__')) >= expected
+    True
+
+    >>> from test.support import HAVE_DOCSTRINGS
+    >>> print(g.__next__.__doc__ if HAVE_DOCSTRINGS else 'Implement next(self).')  # TODO: RUSTPYTHON # doctest: +EXPECTED_FAILURE
+    Implement next(self).
+    >>> import types
+    >>> isinstance(g, types.GeneratorType)
+    True
+
+Check the __iter__ slot is defined to return self
+
+    >>> iter(g) is g
+    True
+
+Verify that the running flag is set properly
+
+    >>> g = (me.gi_running for i in (0,1))
+    >>> me = g
+    >>> me.gi_running
+    0
+    >>> next(me)
+    1
+    >>> me.gi_running
+    0
+
+Verify that genexps are weakly referencable
+
+    >>> import weakref
+    >>> g = (i*i for i in range(4))
+    >>> wr = weakref.ref(g)
+    >>> wr() is g
+    True
+    >>> p = weakref.proxy(g)
+    >>> list(p)
+    [0, 1, 4, 9]
+
+
+"""
+
+# Trace function can throw off the tuple reuse test.
+if hasattr(sys, 'gettrace') and sys.gettrace():
+    __test__ = {}
+else:
+    __test__ = {'doctests' : doctests}
+
+def load_tests(loader, tests, pattern):
+    from test.support.rustpython import DocTestChecker  # TODO: RUSTPYTHON
+    tests.addTest(doctest.DocTestSuite(checker=DocTestChecker()))  # TODO: RUSTPYTHON
+    return tests
+
+
+if __name__ == "__main__":
+    unittest.main()