# Tests for extended unpacking, starred expressions.
import doctest
import unittest
doctests = """
Unpack tuple
>>> t = (1, 2, 3)
>>> a, *b, c = t
>>> a == 1 and b == [2] and c == 3
True
Unpack list
>>> l = [4, 5, 6]
>>> a, *b = l
>>> a == 4 and b == [5, 6]
True
Unpack implied tuple
>>> *a, = 7, 8, 9
>>> a == [7, 8, 9]
True
Unpack nested implied tuple
>>> [*[*a]] = [[7,8,9]]
>>> a == [[7,8,9]]
True
Unpack string... fun!
>>> a, *b = 'one'
>>> a == 'o' and b == ['n', 'e']
True
Unpack long sequence
>>> a, b, c, *d, e, f, g = range(10)
>>> (a, b, c, d, e, f, g) == (0, 1, 2, [3, 4, 5, 6], 7, 8, 9)
True
Unpack short sequence
>>> a, *b, c = (1, 2)
>>> a == 1 and c == 2 and b == []
True
Unpack generic sequence
>>> class Seq:
... def __getitem__(self, i):
... if i >= 0 and i < 3: return i
... raise IndexError
...
>>> a, *b = Seq()
>>> a == 0 and b == [1, 2]
True
Unpack in for statement
>>> for a, *b, c in [(1,2,3), (4,5,6,7)]:
... print(a, b, c)
...
1 [2] 3
4 [5, 6] 7
Unpack in list
>>> [a, *b, c] = range(5)
>>> a == 0 and b == [1, 2, 3] and c == 4
True
Multiple targets
>>> a, *b, c = *d, e = range(5)
>>> a == 0 and b == [1, 2, 3] and c == 4 and d == [0, 1, 2, 3] and e == 4
True
Assignment unpacking
>>> a, b, *c = range(5)
>>> a, b, c
(0, 1, [2, 3, 4])
>>> *a, b, c = a, b, *c
>>> a, b, c
([0, 1, 2], 3, 4)
Set display element unpacking
>>> a = [1, 2, 3]
>>> sorted({1, *a, 0, 4})
[0, 1, 2, 3, 4]
>>> {1, *1, 0, 4}
Traceback (most recent call last):
...
TypeError: 'int' object is not iterable
Dict display element unpacking
>>> kwds = {'z': 0, 'w': 12}
>>> sorted({'x': 1, 'y': 2, **kwds}.items())
[('w', 12), ('x', 1), ('y', 2), ('z', 0)]
>>> sorted({**{'x': 1}, 'y': 2, **{'z': 3}}.items())
[('x', 1), ('y', 2), ('z', 3)]
>>> sorted({**{'x': 1}, 'y': 2, **{'x': 3}}.items())
[('x', 3), ('y', 2)]
>>> sorted({**{'x': 1}, **{'x': 3}, 'x': 4}.items())
[('x', 4)]
>>> {**{}}
{}
>>> a = {}
>>> {**a}[0] = 1
>>> a
{}
>>> {**1}
Traceback (most recent call last):
...
TypeError: 'int' object is not a mapping
>>> {**[]}
Traceback (most recent call last):
...
TypeError: 'list' object is not a mapping
>>> len(eval("{" + ", ".join("**{{{}: {}}}".format(i, i)
... for i in range(1000)) + "}"))
1000
>>> {0:1, **{0:2}, 0:3, 0:4}
{0: 4}
List comprehension element unpacking
>>> a, b, c = [0, 1, 2], 3, 4
>>> [*a, b, c]
[0, 1, 2, 3, 4]
>>> l = [a, (3, 4), {5}, {6: None}, (i for i in range(7, 10))]
>>> [*item for item in l]
Traceback (most recent call last):
...
SyntaxError: iterable unpacking cannot be used in comprehension
>>> [*[0, 1] for i in range(10)]
Traceback (most recent call last):
...
SyntaxError: iterable unpacking cannot be used in comprehension
>>> [*'a' for i in range(10)]
Traceback (most recent call last):
...
SyntaxError: iterable unpacking cannot be used in comprehension
>>> [*[] for i in range(10)]
Traceback (most recent call last):
...
SyntaxError: iterable unpacking cannot be used in comprehension
>>> {**{} for a in [1]}
Traceback (most recent call last):
...
SyntaxError: dict unpacking cannot be used in dict comprehension
# Pegen is better here.
# Generator expression in function arguments
# >>> list(*x for x in (range(5) for i in range(3)))
# Traceback (most recent call last):
# ...
# list(*x for x in (range(5) for i in range(3)))
# ^
# SyntaxError: invalid syntax
>>> dict(**x for x in [{1:2}])
Traceback (most recent call last):
...
dict(**x for x in [{1:2}])
^
SyntaxError: invalid syntax
Iterable argument unpacking
>>> print(*[1], *[2], 3)
1 2 3
Make sure that they don't corrupt the passed-in dicts.
>>> def f(x, y):
... print(x, y)
...
>>> original_dict = {'x': 1}
>>> f(**original_dict, y=2)
1 2
>>> original_dict
{'x': 1}
Now for some failures
Make sure the raised errors are right for keyword argument unpackings
>>> from collections.abc import MutableMapping
>>> class CrazyDict(MutableMapping):
... def __init__(self):
... self.d = {}
...
... def __iter__(self):
... for x in self.d.__iter__():
... if x == 'c':
... self.d['z'] = 10
... yield x
...
... def __getitem__(self, k):
... return self.d[k]
...
... def __len__(self):
... return len(self.d)
...
... def __setitem__(self, k, v):
... self.d[k] = v
...
... def __delitem__(self, k):
... del self.d[k]
...
>>> d = CrazyDict()
>>> d.d = {chr(ord('a') + x): x for x in range(5)}
>>> e = {**d}
Traceback (most recent call last):
...
RuntimeError: dictionary changed size during iteration
>>> d.d = {chr(ord('a') + x): x for x in range(5)}
>>> def f(**kwargs): print(kwargs)
>>> f(**d)
Traceback (most recent call last):
...
RuntimeError: dictionary changed size during iteration
Overridden parameters
>>> f(x=5, **{'x': 3}, y=2)
Traceback (most recent call last):
...
TypeError: test.test_unpack_ex.f() got multiple values for keyword argument 'x'
>>> f(**{'x': 3}, x=5, y=2)
Traceback (most recent call last):
...
TypeError: test.test_unpack_ex.f() got multiple values for keyword argument 'x'
>>> f(**{'x': 3}, **{'x': 5}, y=2)
Traceback (most recent call last):
...
TypeError: test.test_unpack_ex.f() got multiple values for keyword argument 'x'
>>> f(x=5, **{'x': 3}, **{'x': 2})
Traceback (most recent call last):
...
TypeError: test.test_unpack_ex.f() got multiple values for keyword argument 'x'
>>> f(**{1: 3}, **{1: 5})
Traceback (most recent call last):
...
TypeError: test.test_unpack_ex.f() got multiple values for keyword argument '1'
Unpacking non-sequence
>>> a, *b = 7
Traceback (most recent call last):
...
TypeError: cannot unpack non-iterable int object
Unpacking sequence too short
>>> a, *b, c, d, e = Seq()
Traceback (most recent call last):
...
ValueError: not enough values to unpack (expected at least 4, got 3)
Unpacking sequence too short and target appears last
>>> a, b, c, d, *e = Seq()
Traceback (most recent call last):
...
ValueError: not enough values to unpack (expected at least 4, got 3)
Unpacking a sequence where the test for too long raises a different kind of
error
>>> class BozoError(Exception):
... pass
...
>>> class BadSeq:
... def __getitem__(self, i):
... if i >= 0 and i < 3:
... return i
... elif i == 3:
... raise BozoError
... else:
... raise IndexError
...
Trigger code while not expecting an IndexError (unpack sequence too long, wrong
error)
>>> a, *b, c, d, e = BadSeq()
Traceback (most recent call last):
...
test.test_unpack_ex.BozoError
Now some general starred expressions (all fail).
>>> a, *b, c, *d, e = range(10) # doctest:+ELLIPSIS
Traceback (most recent call last):
...
SyntaxError: multiple starred expressions in assignment
>>> [*b, *c] = range(10) # doctest:+ELLIPSIS
Traceback (most recent call last):
...
SyntaxError: multiple starred expressions in assignment
>>> a,*b,*c,*d = range(4) # doctest:+ELLIPSIS
Traceback (most recent call last):
...
SyntaxError: multiple starred expressions in assignment
>>> *a = range(10) # doctest:+ELLIPSIS
Traceback (most recent call last):
...
SyntaxError: starred assignment target must be in a list or tuple
>>> *a # doctest:+ELLIPSIS
Traceback (most recent call last):
...
SyntaxError: can't use starred expression here
>>> *1 # doctest:+ELLIPSIS
Traceback (most recent call last):
...
SyntaxError: can't use starred expression here
>>> x = *a # doctest:+ELLIPSIS
Traceback (most recent call last):
...
SyntaxError: can't use starred expression here
>>> (*x),y = 1, 2 # doctest:+ELLIPSIS
Traceback (most recent call last):
...
SyntaxError: cannot use starred expression here
>>> (((*x))),y = 1, 2 # doctest:+ELLIPSIS
Traceback (most recent call last):
...
SyntaxError: cannot use starred expression here
>>> z,(*x),y = 1, 2, 4 # doctest:+ELLIPSIS
Traceback (most recent call last):
...
SyntaxError: cannot use starred expression here
>>> z,(*x) = 1, 2 # doctest:+ELLIPSIS
Traceback (most recent call last):
...
SyntaxError: cannot use starred expression here
>>> ((*x),y) = 1, 2 # doctest:+ELLIPSIS
Traceback (most recent call last):
...
SyntaxError: cannot use starred expression here
Some size constraints (all fail.)
>>> s = ", ".join("a%d" % i for i in range(1<<8)) + ", *rest = range(1<<8 + 1)"
>>> compile(s, 'test', 'exec') # doctest:+ELLIPSIS
Traceback (most recent call last):
...
SyntaxError: too many expressions in star-unpacking assignment
>>> s = ", ".join("a%d" % i for i in range(1<<8 + 1)) + ", *rest = range(1<<8 + 2)"
>>> compile(s, 'test', 'exec') # doctest:+ELLIPSIS
Traceback (most recent call last):
...
SyntaxError: too many expressions in star-unpacking assignment
(there is an additional limit, on the number of expressions after the
'*rest', but it's 1<<24 and testing it takes too much memory.)
"""
__test__ = {'doctests' : doctests}
def load_tests(loader, tests, pattern):
tests.addTest(doctest.DocTestSuite())
return tests
if __name__ == "__main__":
unittest.main()
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