Python 3 初探，第 2 部分: 高级主题

print()

bytes

string

类修饰符

def myMethod(self):
# do something

myMethod = transformMethod(myMethod)

@

@transformMethod
def myMethod(self):
# do something

def mod(method):
method.__name__ = "John"
return method

@mod
def modMe():
pass

print(modMe.__name__)

class myClass:
pass

myClass = doSomethingOrNotWithClass(myClass)

@doSomethingOrNotWithClass
class myClass:
pass

元类

metaclass

>>>aClass = type('className',
(object,),
{'magicMethod': lambda cls : print("blah blah")})

class meta(type):
def __new__(cls, className, baseClasses, dictOfMethods):
return type.__new__(cls, className, baseClasses, dictOfMethods)

只允许关键字的参数

*

*

def meth(*, arg1): pass

class Foo(*bases, **kwds): pass

metaclass

>>>class aClass(baseClass1, baseClass2, metaclass = aMetaClass): pass

__metaclass__

class Test(object):
__metaclass__ = type

__prepare__

def meth():
print("Calling method")

class MyMeta(type):
@classmethod
def __prepare__(cls, name, baseClasses):
return {'meth':meth}

def __new__(cls, name, baseClasses, classdict):
return type.__new__(cls, name, baseClasses, classdict)

class Test(metaclass = MyMeta):
def __init__(self):
pass

attr = 'an attribute'

t = Test()
print(t.attr)

# The custom dictionary
class member_table(dict):
def __init__(self):
self.member_names = []

def __setitem__(self, key, value):
# if the key is not already defined, add to the
# list of keys.
if key not in self:
self.member_names.append(key)

# Call superclass
dict.__setitem__(self, key, value)

# The metaclass
class OrderedClass(type):
# The prepare function
@classmethod
def __prepare__(metacls, name, bases): # No keywords in this case
return member_table()

# The metaclass invocation
def __new__(cls, name, bases, classdict):
# Note that we replace the classdict with a regular
# dict before passing it to the superclass, so that we
# don't continue to record member names after the class
# has been created.
result = type.__new__(cls, name, bases, dict(classdict))
result.member_names = classdict.member_names
return result

抽象基类

ABCMeta

@abstractmethod

@abstractproperty

@abstractmethod

@abstractproperty

>>>from abc import *
>>>class C(metaclass = ABCMeta): pass
>>>c = C()

>>>from abc import *
>>>class C(metaclass = ABCMeta):
...    @abstractmethod
...    def absMethod(self):
...        pass
>>>c = C()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: Can't instantiate abstract class C with abstract methods absMethod

>>>class B(C):
...    def absMethod(self):
...        print("Now a concrete method")
>>>b = B()
>>>b.absMethod()
Now a concrete method

ABCMeta

__instancecheck__

__subclasscheck__

isinstance()

issubclass()

ABCMeta

register()

>>>class TestABC(metaclass=ABCMeta): pass
>>>TestABC.register(list)
>>>TestABC.__instancecheck__([])
True

isinstance(list, TestABC)

__instancecheck__

__issubclass__

__subclasscheck__

__issubclass__

isinstance(subclass, superclass)

superclass.__isinstance__(subclass)

superclass.__instancecheck__(subclass)

collections

>>>from collections import Iterable
>>>issubclass(list, Iterable)
True

Container

Hashable

Iterable

Iterator

Iterable

Sized

Callable

Sequence

Sized

Iterable

Container

MutableSequence

Sequence

Set

Sized

Iterable

Container

MutableSet

Set

Mapping

Sized

Iterable

Container

MutableMapping

Mapping

MappingView

Sized

KeysView

MappingView

Set

ItemsView

MappingView

Set

ValuesView

MappingView

集合

defaultdict

defaultdict

namedtuple()

ABC 类型层次结构

numbers

Number

Complex

Real

Rational

Integral

数值塔（numerical tower）

fractions

Rational

dir(fractions.Fraction)

imag

real

__complex__

Rationals

Reals

Reals

Complex

抛出和捕获异常

except

try . . . except

>>>try:
...    x = float('not a number')
... except (ValueError, NameError):
...    print "can't convert type"

>>> try:
...    x = float('not a number')
... except ValueError, NameError:
...    print "can't convert type"

ValueError

ValueError

NameError

>>> try:
...    x = float('blah')
... except ValueError, NameError:
...    print "NameError is ", NameError
...
NameError is invalid literal for float(): not a number

,

as

()

# bind ValueError object to local name ex
try:
x = float('blah')
except ValueError as ex:
print("value exception occurred ", ex)

# catch two different exceptions simultaneously
try:
x = float('blah')
except (ValueError, NameError):
print("caught both types of exceptions")

def divide(a, b):
try:
print(a/b)
except Exception as exc:
def log(exc):
fid = open('logfile.txt') # missing 'w'
print(exc, file=fid)
fid.close()

log(exc)

divide(1,0)

divide()

ZeroDivisionError

log()

print(exc, file=fid)

Traceback (most recent call last):
File "chainExceptionExample1.py", line 3, in divide
print(a/b)
ZeroDivisionError: int division or modulo by zero

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "chainExceptionExample1.py", line 12, in <module>
divide(1,0)
File "chainExceptionExample1.py", line 10, in divide
log(exc)
File "chainExceptionExample1.py", line 7, in log
print(exc, file=fid)
File "/opt/python3.0/lib/python3.0/io.py", line 1492, in write
self.buffer.write(b)
File "/opt/python3.0/lib/python3.0/io.py", line 696, in write
self._unsupported("write")
File "/opt/python3.0/lib/python3.0/io.py", line 322, in _unsupported
(self.__class__.__name__, name))
io.UnsupportedOperation: BufferedReader.write() not supported

ZeroDivisionError

__context__

ZeroDivisionError

IOError

__context__

__context__

ZeroDivisionError

__context__

__cause__

None

__cause__

>>> raise EXCEPTION from CAUSE

>>>exception = EXCEPTION
>>>exception.__cause__ = CAUSE
>>>raise exception

class CustomError(Exception):
pass

try:
fid = open("aFile.txt") # missing 'w' again
print("blah blah blah", file=fid)
except IOError as exc:
raise CustomError('something went wrong') from exc

print()

Traceback (most recent call last):
File "chainExceptionExample2.py", line 5, in <module>
fid = open("aFile.txt")
File "/opt/python3.0/lib/python3.0/io.py", line 278, in __new__
return open(*args, **kwargs)
File "/opt/python3.0/lib/python3.0/io.py", line 222, in open
closefd)
File "/opt/python3.0/lib/python3.0/io.py", line 615, in __init__
_fileio._FileIO.__init__(self, name, mode, closefd)
IOError: [Errno 2] No such file or directory: 'aFile.txt'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
File "chainExceptionExample2.py", line 8, in <modulei>
raise CustomError('something went wrong') from exc
__main__.CustomError: something went wrong

CustomError

__traceback__

__traceback__

from traceback import format_tb

try:
1/0
except Exception as exc:
print(format_tb(exc.__traceback__)[0])

format_tb

with 语句

with

__future__

整数支持和语法

0o

0O

>>>0o13
11

0b

0B

>>>0b010101
21

oct()

hex()

函数注释

def methodName(param1: expression1, ..., paramN: expressionN)->ExpressionForReturnType:
...

def execute(program:"name of program to be executed", error:"if something goes wrong"):
...

def getName() -> "isString":
...

结束语

意外收获

antigravity

import antigravity