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) >>> 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 "", line 1, in -toplevel- next(g) StopIteration Does it stay stopped? >>> next(g) Traceback (most recent call last): File "", 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)) 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))) #doctest: +ELLIPSIS {'a': 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 that the outermost for-expression makes an immediate check for iterability >>> (i for i in 6) Traceback (most recent call last): File "", line 1, in -toplevel- (i for i in 6) TypeError: 'int' object is not iterable 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 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 Traceback (most recent call last): ... SyntaxError: cannot assign to generator expression >>> (y for y in (1,2)) += 10 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 "", line 1, in -toplevel- next(me) File "", line 1, in 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 "", line 1, in -toplevel- next(g) File "", line 1, in g = (10 // i for i in (5, 0, 2)) ZeroDivisionError: integer division or modulo by zero >>> next(g) Traceback (most recent call last): File "", 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).') 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] """ import sys # Trace function can throw off the tuple reuse test. if hasattr(sys, 'gettrace') and sys.gettrace(): __test__ = {} else: __test__ = {'doctests' : doctests} def test_main(verbose=None): from test import support from test import test_genexps support.run_doctest(test_genexps, verbose) # verify reference counting if verbose and hasattr(sys, "gettotalrefcount"): import gc counts = [None] * 5 for i in range(len(counts)): support.run_doctest(test_genexps, verbose) gc.collect() counts[i] = sys.gettotalrefcount() print(counts) if __name__ == "__main__": test_main(verbose=True)