python_9(获取字典值、函数参数、函数返回值、lambda的函数用法)
如果我们需要获取字典值的话，我们有两种方法，一个是通过dict[‘key’],另外一个就是dict.get()方法
#获取字典值
info = {'1':'first','2':'second','3':'third'}
number = raw_input('input type you number:')
print info.get(number,'error')
#实例1
#!/usr/bin/python
# -*- coding: UTF-8 -*-
# 函数的定义
from __future__ import division
def arithmetic(x, y, operator):
result = {
"+" : x + y,
"-" : x - y,
"*" : x * y,
"/" : x / y
}
return result.get(operator) # 返回计算结果
# 函数的调用
print arithmetic(1, 2, "+")———————–函数的参数—————————
#!/usr/bin/python
# -*- coding: UTF-8 -*-
from __future__ import division
def append(args=[]):
if len(args) <= 0:
args = []
args.append(0)
print args
append()
append([1])
append()
# 函数的缺省参数
def arithmetic(x=1, y=1, operator="+"):
result = {
"+" : x + y,
"-" : x - y,
"*" : x * y,
"/" : x / y
}
return result.get(operator) # 返回计算结果
print arithmetic(1, 2)
print arithmetic(1, 2, "-")
print arithmetic(y=3, operator="-")
print arithmetic(x=4, operator="-")
print arithmetic(y=3, x=4, operator="-")
# 列表作为参数传递
def arithmetic(args=[], operator="+"):
x = args[0]
y = args[1]
result = {
"+" : x + y,
"-" : x - y,
"*" : x * y,
"/" : x / y
}
return result.get(operator) # 返回计算结果
print arithmetic([1, 2])
# 传递可变参数
def func(*args):
print args
func(1, 2, 3)
# 传递可变参数
def search(*t, **d):
keys = d.keys()
values = d.values()
print keys
print values
for arg in t:
for key in keys:
if arg == key:
print "find:",d[key]
search("one", "three", one="1",two="2",three="3")
#输出结果
>>>
[0]
[1, 0]
[0]
3
-1
-2
3
1
3
(1, 2, 3)
['three', 'two', 'one']
['3', '2', '1']
find: 1
find: 3
>>> ————————函数返回值——————————
#!/usr/bin/python
# -*- coding: UTF-8 -*-
# return语句
from __future__ import division
def arithmetic(x, y, operator):
result = {
"+" : x + y,
"-" : x - y,
"*" : x * y,
"/" : x / y
}
return result.get(operator) # 返回计算结果
# 没有return语句的函数返回None
def func():
pass
print func()
# return后不带参数
def func():
return
print func()
# return返回多个值
def func(x, y, z):
l = [x, y, z]
l.reverse()
numbers = tuple(l)
return numbers
x, y, z = func(0, 1, 2)
print x, y, z
# return返回多个值
def func(x, y, z):
l = [x, y, z]
l.reverse()
a, b, c = tuple(l)
return a, b, c
x, y, z = func(0, 1, 2)
print x, y, z
# 多个return语句
def func(x):
if x > 0:
return "x > 0"
elif x == 0:
return "x == 0"
else:
return "x < 0"
print func(-2)
# 多个return语句的重构
def func(x):
if x > 0:
result = "x > 0"
elif x == 0:
result = "x == 0"
else:
result = "x < 0"
return result
print func(-2) ——————-嵌套函数、内部函数———————————-
#!/usr/bin/python
# -*- coding: UTF-8 -*-
# 嵌套函数
def sum(a, b):
return a + b
def sub(a, b):
return a - b
def func():
x = 1
y = 2
m = 3
n = 4
return sum(x, y) * sub(m, n)
print func()
# 调用内部函数
def func():
x = 1
y = 2
m = 3
n = 4
def sum(a, b): # 内部函数
return a + b
def sub(a, b): # 内部函数
return a - b
return sum(x, y) * sub(m, n)
print func()
# 内部函数直接使用外层函数的变量
def func():
x = 1
y = 2
m = 3
n = 4
def sum(): # 内部函数
return x + y
def sub(): # 内部函数
return m - n
return sum() * sub()
print func()—————-计算阶乘——————-
#!/usr/bin/python
# -*- coding: UTF-8 -*-
# 计算阶乘
def refunc(n):
i = 1
if n > 1: # 递归的结束判断
i = n
n = n * refunc(n-1) # 递推
print "%d! =" %i, n
return n # 回归
refunc(5)
# 使用reduce计算阶乘
print "5! =", reduce(lambda x, y: x * y, range(1, 6))—————-lambda的函数用法—————————-
#!/usr/bin/python
# -*- coding: UTF-8 -*-
# lambda
def func():
x = 1
y = 2
m = 3
n = 4
sum = lambda x, y : x + y
print sum
sub = lambda m, n : m - n
print sub
return sum(x, y) * sub(m, n)
print func()
# lambda的函数用法
print (lambda x: -x)(-2)#!/usr/bin/python
# -*- coding: UTF-8 -*-
# 定义Generator函数
def func(n):
for i in range(n):
yield i
# 在for循环中输出
for i in func(3):
print i
# 使用next()输出
r = func(3)
print r.next()
print r.next()
print r.next()
#print r.next()
# yield与return区别
def func(n):
for i in range(n):
return i
def func2(n):
for i in range(n):
yield i
print func(3)
f = func2(3)
print f
print f.next()
print f.next()
#输出
>>>
0
1
2
0
1
2
0
0x0000000002B97CF0>
0
1
>>>