140 lines
2.9 KiB
Python
140 lines
2.9 KiB
Python
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simple_tests = """
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Let's try a simple generator:
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>>> def f():
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... yield 1
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... yield 2
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>>> g = f()
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>>> g.next()
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1
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>>> g.next()
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2
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>>> g.next()
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Traceback (most recent call last):
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File "<stdin>", line 1, in ?
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File "<stdin>", line 2, in g
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StopIteration
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"return" stops the generator:
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>>> def f():
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... yield 1
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... return
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... yield 2 # never reached
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...
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>>> g = f()
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>>> g.next()
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1
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>>> g.next()
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Traceback (most recent call last):
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File "<stdin>", line 1, in ?
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File "<stdin>", line 3, in f
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StopIteration
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>>> g.next() # once stopped, can't be resumed
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Traceback (most recent call last):
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File "<stdin>", line 1, in ?
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StopIteration
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"raise StopIteration" stops the generator too:
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>>> def f():
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... yield 1
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... return
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... yield 2 # never reached
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...
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>>> g = f()
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>>> g.next()
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1
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>>> g.next()
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Traceback (most recent call last):
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File "<stdin>", line 1, in ?
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StopIteration
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>>> g.next()
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Traceback (most recent call last):
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File "<stdin>", line 1, in ?
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StopIteration
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However, they are not exactly equivalent:
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>>> def g1():
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... try:
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... return
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... except:
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... yield 1
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...
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>>> list(g1())
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[]
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>>> def g2():
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... try:
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... raise StopIteration
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... except:
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... yield 42
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>>> print list(g2())
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[42]
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This may be surprising at first:
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>>> def g3():
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... try:
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... return
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... finally:
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... yield 1
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...
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>>> list(g3())
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[1]
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Let's create an alternate range() function implemented as a generator:
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>>> def yrange(n):
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... for i in range(n):
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... yield i
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...
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>>> list(yrange(5))
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[0, 1, 2, 3, 4]
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Generators always return to the most recent caller:
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>>> def creator():
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... r = yrange(5)
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... print "creator", r.next()
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... return r
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...
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>>> def caller():
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... r = creator()
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... for i in r:
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... print "caller", i
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...
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>>> caller()
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creator 0
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caller 1
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caller 2
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caller 3
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caller 4
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Generators can call other generators:
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>>> def zrange(n):
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... for i in yrange(n):
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... yield i
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...
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>>> list(zrange(5))
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[0, 1, 2, 3, 4]
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"""
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__test__ = {"simple": simple_tests}
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# Magic test name that regrtest.py invokes *after* importing this module.
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# This worms around a bootstrap problem.
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# Note that doctest and regrtest both look in sys.argv for a "-v" argument,
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# so this works as expected in both ways of running regrtest.
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def test_main():
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import doctest, test_generators
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doctest.testmod(test_generators)
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# This part isn't needed for regrtest, but for running the test directly.
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if __name__ == "__main__":
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test_main()
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