python (3.11.7)
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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))
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 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 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 "<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: integer division or modulo 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).')
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]
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