Python基础教程（6）--抽象

标签（空格分隔）： 参数 作用域 (个人总结学习) 懒惰即美德

• 抽象
• 函数调用 抽象和结构 创建函数
• hasattr(func,__call__):判断函数是否可调用
• 斐波那契数列

  def fibs(num):
  result = [0, 1]
  for i in range(num -2):
      result.append(result[-2] + result[-1])
  return result

  记录函数

• 字符串文档

  >>>square.__doc__

  并非真正函数的函数

• 无返回值的函数返回None 参数
• 形参和实参
• 参数可以改变吗？

  函数内参数重新绑定，不会影响函数外部的变量，因为参数存储在局部作用域

• 传入列表

  change(name[:])
  change(names)

• 查询联系人

  
  def lookup(data, label, name):
  return data[label].get(name)

def store(data, full_name):
names = full_name.split()
if len(names) == 2: names.insert(1,'')
lables = 'first', 'middle', 'last'
for label, name in zip(labels, names)
people = lookup(data, label, name)
if people:
people.append(full_name)
else:
data[label][name] = [full_name]

###关键字参数和默认值
###收集参数

 - *params

```python
def print_param(title,*params):
    print(title)
    print(params)

• **keys

  
  def print_params(title,*params, **keys):
  print(title)
  print(params)
  print(keys)

print_params("hello",2,3,4, foo1='23',foo2='34'):

 - 实现多个名字存储

 ```python
 def store(data, *full_names):
   for full_name in full_names:
        names = full_name.split()
        if len(names) == 2: names.insert(1,'')
        lables = 'first', 'middle', 'last'
        for label, name in zip(labels, names)
            people = lookup(data, label, name)
            if people:
                people.append(full_name)
            else:
                data[label][name] = [full_name]

反转过程

 params = {'name': 'Sir Robin', 'greeting': 'wellmet'}
 hello(**params)

练习使用参数

def story(**kwds):
    return 'Once upon a time, there was a ' \
           '%(job)s called %(name)s.' % kwds

def power(x, y, *others):
    if others:
        print 'Received redundant parameters:', others
    return pow(x, y)

def interval(start, stop=None, step=1):
    'Imitates range() for step > 0'
    if stop is None:            # If the stop is not supplied...
        start, stop = 0, start   # shuffle the parameters
    result = []
    i = start                   # We start counting at the start index
    while i < stop:             # Until the index reaches the stop index...
        result.append(i)         # ...append the index to out result...
        i += step                # ...increment the index with the step (> 0) 
    return result

作用域

• 命名空间：作用域，不可见字典
• Shadowing

  globals().['parameter']
  vars
  locals
  nonlocal

递归

• 最小可能性问题
• 递归实例

阶乘和幂

另外一个经典：二元查找

 def search(sequence, number, lower, upper=None):
    if upper is None: upper = len(sequence)-1
    if lower == upper:
        assert number == sequence[upper]
        return upper
    else:
        middle = (lower + upper) // 2
        if number > sequence[middle]:
            return search(sequence, number, middle+1, upper)
        else:
            return search(sequence, number, lower, middle)

本章新函数

• map(func, seq[, seq,...])
• filter(func,seq)
• reduce(func, seq[, initial])
• sum(seq)
• apply(func[, args[, kwargs]])