You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
488 lines
12 KiB
488 lines
12 KiB
# This contains most of the executable examples from Guido's descr
|
|
# tutorial, once at
|
|
#
|
|
# http://www.python.org/2.2/descrintro.html
|
|
#
|
|
# A few examples left implicit in the writeup were fleshed out, a few were
|
|
# skipped due to lack of interest (e.g., faking super() by hand isn't
|
|
# of much interest anymore), and a few were fiddled to make the output
|
|
# deterministic.
|
|
|
|
from test.support import sortdict
|
|
import pprint
|
|
|
|
class defaultdict(dict):
|
|
def __init__(self, default=None):
|
|
dict.__init__(self)
|
|
self.default = default
|
|
|
|
def __getitem__(self, key):
|
|
try:
|
|
return dict.__getitem__(self, key)
|
|
except KeyError:
|
|
return self.default
|
|
|
|
def get(self, key, *args):
|
|
if not args:
|
|
args = (self.default,)
|
|
return dict.get(self, key, *args)
|
|
|
|
def merge(self, other):
|
|
for key in other:
|
|
if key not in self:
|
|
self[key] = other[key]
|
|
|
|
test_1 = """
|
|
|
|
Here's the new type at work:
|
|
|
|
>>> print(defaultdict) # show our type
|
|
<class 'test.test_descrtut.defaultdict'>
|
|
>>> print(type(defaultdict)) # its metatype
|
|
<class 'type'>
|
|
>>> a = defaultdict(default=0.0) # create an instance
|
|
>>> print(a) # show the instance
|
|
{}
|
|
>>> print(type(a)) # show its type
|
|
<class 'test.test_descrtut.defaultdict'>
|
|
>>> print(a.__class__) # show its class
|
|
<class 'test.test_descrtut.defaultdict'>
|
|
>>> print(type(a) is a.__class__) # its type is its class
|
|
True
|
|
>>> a[1] = 3.25 # modify the instance
|
|
>>> print(a) # show the new value
|
|
{1: 3.25}
|
|
>>> print(a[1]) # show the new item
|
|
3.25
|
|
>>> print(a[0]) # a non-existent item
|
|
0.0
|
|
>>> a.merge({1:100, 2:200}) # use a dict method
|
|
>>> print(sortdict(a)) # show the result
|
|
{1: 3.25, 2: 200}
|
|
>>>
|
|
|
|
We can also use the new type in contexts where classic only allows "real"
|
|
dictionaries, such as the locals/globals dictionaries for the exec
|
|
statement or the built-in function eval():
|
|
|
|
>>> print(sorted(a.keys()))
|
|
[1, 2]
|
|
>>> a['print'] = print # need the print function here
|
|
>>> exec("x = 3; print(x)", a)
|
|
3
|
|
>>> print(sorted(a.keys(), key=lambda x: (str(type(x)), x)))
|
|
[1, 2, '__builtins__', 'print', 'x']
|
|
>>> print(a['x'])
|
|
3
|
|
>>>
|
|
|
|
Now I'll show that defaultdict instances have dynamic instance variables,
|
|
just like classic classes:
|
|
|
|
>>> a.default = -1
|
|
>>> print(a["noway"])
|
|
-1
|
|
>>> a.default = -1000
|
|
>>> print(a["noway"])
|
|
-1000
|
|
>>> 'default' in dir(a)
|
|
True
|
|
>>> a.x1 = 100
|
|
>>> a.x2 = 200
|
|
>>> print(a.x1)
|
|
100
|
|
>>> d = dir(a)
|
|
>>> 'default' in d and 'x1' in d and 'x2' in d
|
|
True
|
|
>>> print(sortdict(a.__dict__))
|
|
{'default': -1000, 'x1': 100, 'x2': 200}
|
|
>>>
|
|
"""
|
|
|
|
class defaultdict2(dict):
|
|
__slots__ = ['default']
|
|
|
|
def __init__(self, default=None):
|
|
dict.__init__(self)
|
|
self.default = default
|
|
|
|
def __getitem__(self, key):
|
|
try:
|
|
return dict.__getitem__(self, key)
|
|
except KeyError:
|
|
return self.default
|
|
|
|
def get(self, key, *args):
|
|
if not args:
|
|
args = (self.default,)
|
|
return dict.get(self, key, *args)
|
|
|
|
def merge(self, other):
|
|
for key in other:
|
|
if key not in self:
|
|
self[key] = other[key]
|
|
|
|
test_2 = """
|
|
|
|
The __slots__ declaration takes a list of instance variables, and reserves
|
|
space for exactly these in the instance. When __slots__ is used, other
|
|
instance variables cannot be assigned to:
|
|
|
|
>>> a = defaultdict2(default=0.0)
|
|
>>> a[1]
|
|
0.0
|
|
>>> a.default = -1
|
|
>>> a[1]
|
|
-1
|
|
>>> a.x1 = 1
|
|
Traceback (most recent call last):
|
|
File "<stdin>", line 1, in ?
|
|
AttributeError: 'defaultdict2' object has no attribute 'x1'
|
|
>>>
|
|
|
|
"""
|
|
|
|
test_3 = """
|
|
|
|
Introspecting instances of built-in types
|
|
|
|
For instance of built-in types, x.__class__ is now the same as type(x):
|
|
|
|
>>> type([])
|
|
<class 'list'>
|
|
>>> [].__class__
|
|
<class 'list'>
|
|
>>> list
|
|
<class 'list'>
|
|
>>> isinstance([], list)
|
|
True
|
|
>>> isinstance([], dict)
|
|
False
|
|
>>> isinstance([], object)
|
|
True
|
|
>>>
|
|
|
|
You can get the information from the list type:
|
|
|
|
>>> pprint.pprint(dir(list)) # like list.__dict__.keys(), but sorted
|
|
['__add__',
|
|
'__class__',
|
|
'__class_getitem__',
|
|
'__contains__',
|
|
'__delattr__',
|
|
'__delitem__',
|
|
'__dir__',
|
|
'__doc__',
|
|
'__eq__',
|
|
'__format__',
|
|
'__ge__',
|
|
'__getattribute__',
|
|
'__getitem__',
|
|
'__gt__',
|
|
'__hash__',
|
|
'__iadd__',
|
|
'__imul__',
|
|
'__init__',
|
|
'__init_subclass__',
|
|
'__iter__',
|
|
'__le__',
|
|
'__len__',
|
|
'__lt__',
|
|
'__mul__',
|
|
'__ne__',
|
|
'__new__',
|
|
'__reduce__',
|
|
'__reduce_ex__',
|
|
'__repr__',
|
|
'__reversed__',
|
|
'__rmul__',
|
|
'__setattr__',
|
|
'__setitem__',
|
|
'__sizeof__',
|
|
'__str__',
|
|
'__subclasshook__',
|
|
'append',
|
|
'clear',
|
|
'copy',
|
|
'count',
|
|
'extend',
|
|
'index',
|
|
'insert',
|
|
'pop',
|
|
'remove',
|
|
'reverse',
|
|
'sort']
|
|
|
|
The new introspection API gives more information than the old one: in
|
|
addition to the regular methods, it also shows the methods that are
|
|
normally invoked through special notations, e.g. __iadd__ (+=), __len__
|
|
(len), __ne__ (!=). You can invoke any method from this list directly:
|
|
|
|
>>> a = ['tic', 'tac']
|
|
>>> list.__len__(a) # same as len(a)
|
|
2
|
|
>>> a.__len__() # ditto
|
|
2
|
|
>>> list.append(a, 'toe') # same as a.append('toe')
|
|
>>> a
|
|
['tic', 'tac', 'toe']
|
|
>>>
|
|
|
|
This is just like it is for user-defined classes.
|
|
"""
|
|
|
|
test_4 = """
|
|
|
|
Static methods and class methods
|
|
|
|
The new introspection API makes it possible to add static methods and class
|
|
methods. Static methods are easy to describe: they behave pretty much like
|
|
static methods in C++ or Java. Here's an example:
|
|
|
|
>>> class C:
|
|
...
|
|
... @staticmethod
|
|
... def foo(x, y):
|
|
... print("staticmethod", x, y)
|
|
|
|
>>> C.foo(1, 2)
|
|
staticmethod 1 2
|
|
>>> c = C()
|
|
>>> c.foo(1, 2)
|
|
staticmethod 1 2
|
|
|
|
Class methods use a similar pattern to declare methods that receive an
|
|
implicit first argument that is the *class* for which they are invoked.
|
|
|
|
>>> class C:
|
|
... @classmethod
|
|
... def foo(cls, y):
|
|
... print("classmethod", cls, y)
|
|
|
|
>>> C.foo(1)
|
|
classmethod <class 'test.test_descrtut.C'> 1
|
|
>>> c = C()
|
|
>>> c.foo(1)
|
|
classmethod <class 'test.test_descrtut.C'> 1
|
|
|
|
>>> class D(C):
|
|
... pass
|
|
|
|
>>> D.foo(1)
|
|
classmethod <class 'test.test_descrtut.D'> 1
|
|
>>> d = D()
|
|
>>> d.foo(1)
|
|
classmethod <class 'test.test_descrtut.D'> 1
|
|
|
|
This prints "classmethod __main__.D 1" both times; in other words, the
|
|
class passed as the first argument of foo() is the class involved in the
|
|
call, not the class involved in the definition of foo().
|
|
|
|
But notice this:
|
|
|
|
>>> class E(C):
|
|
... @classmethod
|
|
... def foo(cls, y): # override C.foo
|
|
... print("E.foo() called")
|
|
... C.foo(y)
|
|
|
|
>>> E.foo(1)
|
|
E.foo() called
|
|
classmethod <class 'test.test_descrtut.C'> 1
|
|
>>> e = E()
|
|
>>> e.foo(1)
|
|
E.foo() called
|
|
classmethod <class 'test.test_descrtut.C'> 1
|
|
|
|
In this example, the call to C.foo() from E.foo() will see class C as its
|
|
first argument, not class E. This is to be expected, since the call
|
|
specifies the class C. But it stresses the difference between these class
|
|
methods and methods defined in metaclasses (where an upcall to a metamethod
|
|
would pass the target class as an explicit first argument).
|
|
"""
|
|
|
|
test_5 = """
|
|
|
|
Attributes defined by get/set methods
|
|
|
|
|
|
>>> class property(object):
|
|
...
|
|
... def __init__(self, get, set=None):
|
|
... self.__get = get
|
|
... self.__set = set
|
|
...
|
|
... def __get__(self, inst, type=None):
|
|
... return self.__get(inst)
|
|
...
|
|
... def __set__(self, inst, value):
|
|
... if self.__set is None:
|
|
... raise AttributeError("this attribute is read-only")
|
|
... return self.__set(inst, value)
|
|
|
|
Now let's define a class with an attribute x defined by a pair of methods,
|
|
getx() and setx():
|
|
|
|
>>> class C(object):
|
|
...
|
|
... def __init__(self):
|
|
... self.__x = 0
|
|
...
|
|
... def getx(self):
|
|
... return self.__x
|
|
...
|
|
... def setx(self, x):
|
|
... if x < 0: x = 0
|
|
... self.__x = x
|
|
...
|
|
... x = property(getx, setx)
|
|
|
|
Here's a small demonstration:
|
|
|
|
>>> a = C()
|
|
>>> a.x = 10
|
|
>>> print(a.x)
|
|
10
|
|
>>> a.x = -10
|
|
>>> print(a.x)
|
|
0
|
|
>>>
|
|
|
|
Hmm -- property is builtin now, so let's try it that way too.
|
|
|
|
>>> del property # unmask the builtin
|
|
>>> property
|
|
<class 'property'>
|
|
|
|
>>> class C(object):
|
|
... def __init__(self):
|
|
... self.__x = 0
|
|
... def getx(self):
|
|
... return self.__x
|
|
... def setx(self, x):
|
|
... if x < 0: x = 0
|
|
... self.__x = x
|
|
... x = property(getx, setx)
|
|
|
|
|
|
>>> a = C()
|
|
>>> a.x = 10
|
|
>>> print(a.x)
|
|
10
|
|
>>> a.x = -10
|
|
>>> print(a.x)
|
|
0
|
|
>>>
|
|
"""
|
|
|
|
test_6 = """
|
|
|
|
Method resolution order
|
|
|
|
This example is implicit in the writeup.
|
|
|
|
>>> class A: # implicit new-style class
|
|
... def save(self):
|
|
... print("called A.save()")
|
|
>>> class B(A):
|
|
... pass
|
|
>>> class C(A):
|
|
... def save(self):
|
|
... print("called C.save()")
|
|
>>> class D(B, C):
|
|
... pass
|
|
|
|
>>> D().save()
|
|
called C.save()
|
|
|
|
>>> class A(object): # explicit new-style class
|
|
... def save(self):
|
|
... print("called A.save()")
|
|
>>> class B(A):
|
|
... pass
|
|
>>> class C(A):
|
|
... def save(self):
|
|
... print("called C.save()")
|
|
>>> class D(B, C):
|
|
... pass
|
|
|
|
>>> D().save()
|
|
called C.save()
|
|
"""
|
|
|
|
class A(object):
|
|
def m(self):
|
|
return "A"
|
|
|
|
class B(A):
|
|
def m(self):
|
|
return "B" + super(B, self).m()
|
|
|
|
class C(A):
|
|
def m(self):
|
|
return "C" + super(C, self).m()
|
|
|
|
class D(C, B):
|
|
def m(self):
|
|
return "D" + super(D, self).m()
|
|
|
|
|
|
test_7 = """
|
|
|
|
Cooperative methods and "super"
|
|
|
|
>>> print(D().m()) # "DCBA"
|
|
DCBA
|
|
"""
|
|
|
|
test_8 = """
|
|
|
|
Backwards incompatibilities
|
|
|
|
>>> class A:
|
|
... def foo(self):
|
|
... print("called A.foo()")
|
|
|
|
>>> class B(A):
|
|
... pass
|
|
|
|
>>> class C(A):
|
|
... def foo(self):
|
|
... B.foo(self)
|
|
|
|
>>> C().foo()
|
|
called A.foo()
|
|
|
|
>>> class C(A):
|
|
... def foo(self):
|
|
... A.foo(self)
|
|
>>> C().foo()
|
|
called A.foo()
|
|
"""
|
|
|
|
__test__ = {"tut1": test_1,
|
|
"tut2": test_2,
|
|
"tut3": test_3,
|
|
"tut4": test_4,
|
|
"tut5": test_5,
|
|
"tut6": test_6,
|
|
"tut7": test_7,
|
|
"tut8": test_8}
|
|
|
|
# Magic test name that regrtest.py invokes *after* importing this module.
|
|
# This worms around a bootstrap problem.
|
|
# Note that doctest and regrtest both look in sys.argv for a "-v" argument,
|
|
# so this works as expected in both ways of running regrtest.
|
|
def test_main(verbose=None):
|
|
# Obscure: import this module as test.test_descrtut instead of as
|
|
# plain test_descrtut because the name of this module works its way
|
|
# into the doctest examples, and unless the full test.test_descrtut
|
|
# business is used the name can change depending on how the test is
|
|
# invoked.
|
|
from test import support, test_descrtut
|
|
support.run_doctest(test_descrtut, verbose)
|
|
|
|
# This part isn't needed for regrtest, but for running the test directly.
|
|
if __name__ == "__main__":
|
|
test_main(1)
|