Viewing file:  test_listcomps.py (4.17 KB) -rw-r--r--
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doctests = """
########### Tests borrowed from or inspired by test_genexps.py ############
Test simple loop with conditional
>>> sum([i*i for i in range(100) if i&1 == 1])
166650
Test simple nesting
>>> [(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
>>> [(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.
>>> [j*j for i in range(4) for j in [i+1]]
[1, 4, 9, 16]
>>> [j*k for i in range(4) for j in [i+1] for k in [j+1]]
[2, 6, 12, 20]
>>> [j*k for i in range(4) for j, k in [(i+1, i+2)]]
[2, 6, 12, 20]
Not assignment
>>> [i*i for i in [*range(4)]]
[0, 1, 4, 9]
>>> [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
Verify that syntax error's are raised for listcomps used as lvalues
>>> [y for y in (1,2)] = 10 # doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
...
SyntaxError: ...
>>> [y for y in (1,2)] += 10 # doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
...
SyntaxError: ...
########### Tests borrowed from or inspired by test_generators.py ############
Make a nested list comprehension that acts like range()
>>> def frange(n):
... return [i for i in range(n)]
>>> frange(10)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
Same again, only as a lambda expression instead of a function definition
>>> lrange = lambda n: [i for i in range(n)]
>>> lrange(10)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
Generators can call other generators:
>>> def grange(n):
... for x in [i for i in range(n)]:
... yield x
>>> list(grange(5))
[0, 1, 2, 3, 4]
Make sure that None is a valid return value
>>> [None for i in range(10)]
[None, None, None, None, None, None, None, None, None, None]
########### Tests for various scoping corner cases ############
Return lambdas that use the iteration variable as a default argument
>>> items = [(lambda i=i: i) for i in range(5)]
>>> [x() for x in items]
[0, 1, 2, 3, 4]
Same again, only this time as a closure variable
>>> items = [(lambda: i) for i in range(5)]
>>> [x() for x in items]
[4, 4, 4, 4, 4]
Another way to test that the iteration variable is local to the list comp
>>> items = [(lambda: i) for i in range(5)]
>>> i = 20
>>> [x() for x in items]
[4, 4, 4, 4, 4]
And confirm that a closure can jump over the list comp scope
>>> items = [(lambda: y) for i in range(5)]
>>> y = 2
>>> [x() for x in items]
[2, 2, 2, 2, 2]
We also repeat each of the above scoping tests inside a function
>>> def test_func():
... items = [(lambda i=i: i) for i in range(5)]
... return [x() for x in items]
>>> test_func()
[0, 1, 2, 3, 4]
>>> def test_func():
... items = [(lambda: i) for i in range(5)]
... return [x() for x in items]
>>> test_func()
[4, 4, 4, 4, 4]
>>> def test_func():
... items = [(lambda: i) for i in range(5)]
... i = 20
... return [x() for x in items]
>>> test_func()
[4, 4, 4, 4, 4]
>>> def test_func():
... items = [(lambda: y) for i in range(5)]
... y = 2
... return [x() for x in items]
>>> test_func()
[2, 2, 2, 2, 2]
"""
__test__ = {'doctests' : doctests}
def test_main(verbose=None):
import sys
from test import support
from test import test_listcomps
support.run_doctest(test_listcomps, 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_listcomps, verbose)
gc.collect()
counts[i] = sys.gettotalrefcount()
print(counts)
if __name__ == "__main__":
test_main(verbose=True)
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