初学Python函数的笔记整理

def my_abs(x):
  if x >= 0:
    return x
  else:
    return -x
 

import math
 
def move(x, y, step, angle=0):
  nx = x + step * math.cos(angle)
  ny = y - step * math.sin(angle)
  return nx, ny

def nop():
  pass

def power(x, n=2):
  s = 1
  while n > 0:
    n = n - 1
    s = s * x
  return s

def calc(*numbers):
  sum = 0
  for n in numbers:
    sum = sum + n * n
  return sum

> calc(1, 2)
5
> calc()
0
> nums = [1, 2, 3]
> calc(*nums)
14

def person(name, age, **kw):
  print 'name:', name, 'age:', age, 'other:', kw

> person('Michael', 30)
name: Michael age: 30 other: {}
> person('Bob', 35, city='Beijing')
name: Bob age: 35 other: {'city': 'Beijing'}
> person('Adam', 45, gender='M', job='Engineer')
name: Adam age: 45 other: {'gender': 'M', 'job': 'Engineer'}
> kw = {'city': 'Beijing', 'job': 'Engineer'}
> person('Jack', 24, **kw)
name: Jack age: 24 other: {'city': 'Beijing', 'job': 'Engineer'}

> def f(x):
...   return x * x
...
> map(f, [1, 2, 3, 4, 5, 6, 7, 8, 9])
[1, 4, 9, 16, 25, 36, 49, 64, 81]

reduce(f, [x1, x2, x3, x4])
#相当于：
f(f(f(x1, x2), x3), x4)
 
> def add(x, y):
...   return x + y
...
> reduce(add, [1, 3, 5, 7, 9])
25

def is_odd(n):
  return n % 2 == 1
 
filter(is_odd, [1, 2, 4, 5, 6, 9, 10, 15])
# 结果: [1, 5, 9, 15]

> sorted([36, 5, 12, 9, 21])
[5, 9, 12, 21, 36]

def reversed_cmp(x, y):
  if x > y:
    return -1
  if x < y:
    return 1
  return 0
 
> sorted([36, 5, 12, 9, 21], reversed_cmp)
[36, 21, 12, 9, 5]

def lazy_sum(*args):
  def sum():
    ax = 0
    for n in args:
      ax = ax + n
    return ax
  return sum
 
> f = lazy_sum(1, 3, 5, 7, 9)
> f
<function sum at 0x10452f668>
> f()
25

def count():
  fs = []
  for i in range(1, 4):
    def f():
       return i*i
    fs.append(f)
  return fs
 
f1, f2, f3 = count()
> f1()
9
> f2()
9
> f3()
9

def f(x):
  return x * x

def build(x, y):
  return lambda: x * x + y * y

def log(func):
  def wrapper(*args, **kw):
    print 'call %s():' % func.__name__
    return func(*args, **kw)
  return wrapper
 
@log
def now():
  print '2013-12-25'
 
> now()
call now():
2013-12-25
 
#相当于执行：
 
now = log(now)
回到顶部
带参数的装饰器
 
def log(text):
  def decorator(func):
    def wrapper(*args, **kw):
      print '%s %s():' % (text, func.__name__)
      return func(*args, **kw)
    return wrapper
  return decorator
 
@log('execute')
def now():
  print '2013-12-25'
 
#执行结果
> now()
execute now():
2013-12-25
 
#相当于执行：
 
> now = log('execute')(now)

import functools
 
def log(func):
  @functools.wraps(func)
  def wrapper(*args, **kw):
    print 'call %s():' % func.__name__
    return func(*args, **kw)
  return wrapper
 
#对于带参函数
 
import functools
 
def log(text):
  def decorator(func):
    @functools.wraps(func)
    def wrapper(*args, **kw):
      print '%s %s():' % (text, func.__name__)
      return func(*args, **kw)
    return wrapper
  return decorator

> import functools
> int2 = functools.partial(int, base=2)
> int2('1000000')
64
> int2('1010101')
85
 
#相当于：
 
def int2(x, base=2):
  return int(x, base)
 
max2 = functools.partial(max, 10)

max2(5, 6, 7)
 
#相当于：
 
max(10, 5, 6, 7)