mirror of
https://github.com/python/cpython.git
synced 2024-11-25 10:54:51 +08:00
ee30927b45
Good news: Some of this stuff is pretty sophisticated (read nuts), and I haven't bumped into a bug yet. Bad news: If I run the doctest in an infinite loop, memory is clearly leaking.
463 lines
12 KiB
Python
463 lines
12 KiB
Python
tutorial_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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>>> for i in f():
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... print i
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1
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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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# The examples from PEP 255.
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pep_tests = """
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Specification: Return
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Note that return isn't always equivalent to raising StopIteration: the
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difference lies in how enclosing try/except constructs are treated.
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For example,
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>>> def f1():
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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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>>> print list(f1())
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[]
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because, as in any function, return simply exits, but
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>>> def f2():
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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(f2())
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[42]
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because StopIteration is captured by a bare "except", as is any
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exception.
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Specification: Generators and Exception Propagation
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>>> def f():
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... return 1/0
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>>> def g():
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... yield f() # the zero division exception propagates
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... yield 42 # and we'll never get here
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>>> k = g()
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>>> k.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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File "<stdin>", line 2, in f
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ZeroDivisionError: integer division or modulo by zero
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>>> k.next() # and the generator cannot 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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>>>
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Specification: Try/Except/Finally
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>>> def f():
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... try:
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... yield 1
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... try:
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... yield 2
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... 1/0
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... yield 3 # never get here
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... except ZeroDivisionError:
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... yield 4
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... yield 5
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... raise
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... except:
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... yield 6
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... yield 7 # the "raise" above stops this
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... except:
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... yield 8
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... yield 9
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... try:
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... x = 12
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... finally:
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... yield 10
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... yield 11
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>>> print list(f())
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[1, 2, 4, 5, 8, 9, 10, 11]
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>>>
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Guido's binary tree example.
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>>> # A binary tree class.
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>>> class Tree:
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...
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... def __init__(self, label, left=None, right=None):
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... self.label = label
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... self.left = left
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... self.right = right
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...
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... def __repr__(self, level=0, indent=" "):
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... s = level*indent + `self.label`
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... if self.left:
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... s = s + "\\n" + self.left.__repr__(level+1, indent)
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... if self.right:
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... s = s + "\\n" + self.right.__repr__(level+1, indent)
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... return s
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...
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... def __iter__(self):
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... return inorder(self)
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>>> # Create a Tree from a list.
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>>> def tree(list):
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... n = len(list)
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... if n == 0:
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... return []
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... i = n / 2
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... return Tree(list[i], tree(list[:i]), tree(list[i+1:]))
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>>> # Show it off: create a tree.
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>>> t = tree("ABCDEFGHIJKLMNOPQRSTUVWXYZ")
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>>> # A recursive generator that generates Tree leaves in in-order.
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>>> def inorder(t):
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... if t:
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... for x in inorder(t.left):
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... yield x
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... yield t.label
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... for x in inorder(t.right):
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... yield x
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>>> # Show it off: create a tree.
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... t = tree("ABCDEFGHIJKLMNOPQRSTUVWXYZ")
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... # Print the nodes of the tree in in-order.
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... for x in t:
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... print x,
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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
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>>> # A non-recursive generator.
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>>> def inorder(node):
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... stack = []
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... while node:
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... while node.left:
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... stack.append(node)
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... node = node.left
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... yield node.label
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... while not node.right:
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... try:
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... node = stack.pop()
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... except IndexError:
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... return
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... yield node.label
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... node = node.right
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>>> # Exercise the non-recursive generator.
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>>> for x in t:
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... print x,
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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
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"""
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# A few examples from Iterator-List and Python-Dev email.
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email_tests = """
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The difference between yielding None and returning it.
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>>> def g():
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... for i in range(3):
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... yield None
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... yield None
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... return
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>>> list(g())
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[None, None, None, None]
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Ensure that explicitly raising StopIteration acts like any other exception
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in try/except, not like a return.
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>>> def g():
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... yield 1
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... try:
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... raise StopIteration
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... except:
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... yield 2
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... yield 3
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>>> list(g())
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[1, 2, 3]
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A generator can't be resumed while it's already running.
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>>> def g():
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... i = me.next()
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... yield i
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>>> me = g()
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>>> me.next()
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Traceback (most recent call last):
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...
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File "<string>", line 2, in g
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ValueError: generator already executing
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"""
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# Fun tests (for sufficiently warped notions of "fun").
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fun_tests = """
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Build up to a recursive Sieve of Eratosthenes generator.
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>>> def firstn(g, n):
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... return [g.next() for i in range(n)]
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>>> def intsfrom(i):
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... while 1:
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... yield i
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... i += 1
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>>> firstn(intsfrom(5), 7)
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[5, 6, 7, 8, 9, 10, 11]
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>>> def exclude_multiples(n, ints):
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... for i in ints:
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... if i % n:
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... yield i
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>>> firstn(exclude_multiples(3, intsfrom(1)), 6)
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[1, 2, 4, 5, 7, 8]
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>>> def sieve(ints):
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... prime = ints.next()
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... yield prime
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... not_divisible_by_prime = exclude_multiples(prime, ints)
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... for p in sieve(not_divisible_by_prime):
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... yield p
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>>> primes = sieve(intsfrom(2))
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>>> firstn(primes, 20)
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[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71]
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Another famous problem: generate all integers of the form
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2**i * 3**j * 5**k
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in increasing order, where i,j,k >= 0. Trickier than it may look at first!
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Try writing it without generators, and correctly, and without generating
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3 internal results for each result output.
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>>> def times(n, g):
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... for i in g:
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... yield n * i
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>>> firstn(times(10, intsfrom(1)), 10)
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[10, 20, 30, 40, 50, 60, 70, 80, 90, 100]
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>>> def merge(g, h):
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... ng = g.next()
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... nh = h.next()
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... while 1:
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... if ng < nh:
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... yield ng
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... ng = g.next()
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... elif ng > nh:
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... yield nh
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... nh = h.next()
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... else:
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... yield ng
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... ng = g.next()
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... nh = h.next()
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This works, but is doing a whale of a lot or redundant work -- it's not
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clear how to get the internal uses of m235 to share a single generator.
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Note that me_times2 (etc) each need to see every element in the result
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sequence. So this is an example where lazy lists are more natural (you
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can look at the head of a lazy list any number of times).
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>>> def m235():
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... yield 1
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... me_times2 = times(2, m235())
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... me_times3 = times(3, m235())
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... me_times5 = times(5, m235())
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... for i in merge(merge(me_times2,
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... me_times3),
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... me_times5):
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... yield i
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>>> result = m235()
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>>> for i in range(5):
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... print firstn(result, 15)
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[1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 16, 18, 20, 24]
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[25, 27, 30, 32, 36, 40, 45, 48, 50, 54, 60, 64, 72, 75, 80]
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[81, 90, 96, 100, 108, 120, 125, 128, 135, 144, 150, 160, 162, 180, 192]
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[200, 216, 225, 240, 243, 250, 256, 270, 288, 300, 320, 324, 360, 375, 384]
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[400, 405, 432, 450, 480, 486, 500, 512, 540, 576, 600, 625, 640, 648, 675]
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Heh. Here's one way to get a shared list, complete with an excruciating
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namespace renaming trick. The *pretty* part is that the times() and merge()
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functions can be reused as-is, because they only assume their stream
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arguments are iterable -- a LazyList is the same as a generator to times().
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>>> class LazyList:
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... def __init__(self, g):
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... self.sofar = []
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... self.fetch = g.next
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...
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... def __getitem__(self, i):
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... sofar, fetch = self.sofar, self.fetch
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... while i >= len(sofar):
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... sofar.append(fetch())
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... return sofar[i]
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>>> def m235():
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... yield 1
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... # Gack: m235 below actually refers to a LazyList.
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... me_times2 = times(2, m235)
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... me_times3 = times(3, m235)
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... me_times5 = times(5, m235)
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... for i in merge(merge(me_times2,
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... me_times3),
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... me_times5):
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... yield i
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>>> m235 = LazyList(m235())
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>>> for i in range(5):
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... print [m235[j] for j in range(15*i, 15*(i+1))]
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[1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 16, 18, 20, 24]
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[25, 27, 30, 32, 36, 40, 45, 48, 50, 54, 60, 64, 72, 75, 80]
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[81, 90, 96, 100, 108, 120, 125, 128, 135, 144, 150, 160, 162, 180, 192]
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[200, 216, 225, 240, 243, 250, 256, 270, 288, 300, 320, 324, 360, 375, 384]
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[400, 405, 432, 450, 480, 486, 500, 512, 540, 576, 600, 625, 640, 648, 675]
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"""
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__test__ = {"tut": tutorial_tests,
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"pep": pep_tests,
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"email": email_tests,
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"fun": fun_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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