类的定义、参数声明、数据成员使用详解(9) – python入门教程

# Function defined outside the class 
def f1(self, x, y): 
    return min(x, x+y) 

class C: 
    f = f1 
    def g(self): 
        return 'hello world' 
    h = g

class Bag: 
    def __init__(self): 
        self.data = [] 
    def add(self, x): 
        self.data.append(x) 
    def addtwice(self, x):
        self.add(x) 
        self.add(x)

class DerivedClassName(BaseClassName):
    <statement-1>
    .
    .
    .
    <statement-N>

该名称BaseClassName必须在包含派生类定义的范围内定义。代替基类名称，也允许使用其他任意表达式。这可能很有用，例如，当基类在另一个模块中定义时：

class DerivedClassName(modname.BaseClassName):

class Mapping: 
    def __init__(self, iterable): 
        self.items_list = [] 
        self.__update(iterable) 
    def update(self, iterable): 
        for item in iterable: 
            self.items_list.append(item) 
    __update = update # private copy of original update() method 

class MappingSubclass(Mapping): 
    def update(self, keys, values): 
        # provides new signature for update() 
        # but does not break __init__() 
        for item in zip(keys, values): 
            self.items_list.append(item)

class Employee: 
    pass 

john = Employee() # Create an empty employee record 

# Fill the fields of the record 

john.name = 'John Doe' 
john.dept = 'computer lab' 
john.salary = 1000

for element in [1, 2, 3]: 
    print(element) 

for element in (1, 2, 3): 
    print(element) 

for key in {'one':1, 'two':2}: 
    print(key) 

for char in "123": 
    print(char) 

for line in open("myfile.txt"): 
    print(line, end='')

>>>
>>> s = 'abc'
>>> it = iter(s)
>>> it
<iterator object at 0x00A1DB50>
>>> next(it)
'a'
>>> next(it)
'b'
>>> next(it)
'c'
>>> next(it)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
    next(it)
StopIteration

class Reverse:
    """Iterator for looping over a sequence backwards."""
    def __init__(self, data):
        self.data = data
        self.index = len(data)

    def __iter__(self):
        return self

    def __next__(self):
        if self.index == 0:
            raise StopIteration
        self.index = self.index - 1
        return self.data[self.index]
>>>
>>> rev = Reverse('spam')
>>> iter(rev)
<__main__.Reverse object at 0x00A1DB50>
>>> for char in rev:
...     print(char)
...
m
a
p
s

def reverse(data):
    for index in range(len(data)-1, -1, -1):
        yield data[index]
>>>
>>> for char in reverse('golf'):
...     print(char)
...
f
l
o
g

>>>
>>> sum(i*i for i in range(10))                 # sum of squares
285

>>> xvec = [10, 20, 30]
>>> yvec = [7, 5, 3]
>>> sum(x*y for x,y in zip(xvec, yvec))         # dot product
260

>>> from math import pi, sin
>>> sine_table = {x: sin(x*pi/180) for x in range(0, 91)}

>>> unique_words = set(word  for line in page  for word in line.split())

>>> valedictorian = max((student.gpa, student.name) for student in graduates)

>>> data = 'golf'
>>> list(data[i] for i in range(len(data)-1, -1, -1))
['f', 'l', 'o', 'g']