python
1.函数的定义练习:判断输入的是不是一个数字
- #!/usr/bin/env python
- def isNum():
- sth = raw_input("Please input something: ")
- try:
- if type(int(sth)) == type(1):
- print "%s is a number" % sth
- except Exception:
- print "%s is not a number" % sth
- isNum()
2.函数的参数
练习:判断输入的是不是一个数字
- #!/usr/bin/env python
- import sys
- def isNum(s):
- for i in s:
- if i in "1234567890":
- pass
- else:
- print "%s is not a number" % s
- break
- else:
- print "%s is a number" % s
- isNum(sys.argv[1])
3.函数的默认参数
listdir()函数
练习:判断输入的是不是一个数字
- #!/usr/bin/env python
- import os
- def isNum(s):
- for i in s:
- if i in "1234567890":
- pass
- else:
- break
- else:
- print s
- for i in (os.listdir("/proc")):
- isNum(i)
注:默认参数必须写在后面
- In [3]: def fun(x=1,y):
- ...: print x+y
- File "<ipython-input-3-3b7bae6400b0>", line 1
- def fun(x=1,y):
- SyntaxError: non-default argument follows default argument
- In [4]: def fun(x,y=1):
- ...: print x+y
- ...:
- In [5]: fun(2)
4.1函数变量
练习:函数内部(局部)不能进行全局变量赋值等操作;如果申明成全局变量,才可以
- #!/usr/bin/env python
- x = 1
- def fun():
- global x
- x+=1
- print x
- fun()
- print x
结果:
2
2
练习2:把函数内部变量,申明成全局变量,外部也可以通过函数调用
- #!/usr/bin/env python
- x = 1
- def fun():
- global x
- x += 1
- global y
- y = 3
- print x
- print y
- fun()
- print x
- print y
结果:
2
3
2
3
练习3:locas() :统计变量,返回字典
- #!/usr/bin/env python
- x = 1
- def fun():
- x = 1
- y = 1
- print locals()
- fun()
- print locals()
结果:
- {'y': 1, 'x': 1}
- {'__builtins__': <module '__builtin__' (built-in)>, '__file__': '18.py', '__package__': None, 'x': 1, 'fun': <function fun at 0x7f53bc8938c0>, '__name__': '__main__', '__doc__': None}
5.函数返回值
练习1:默认返回none
- #!/usr/bin/env python
- def fun():
- print "hello,world"
- print fun()
结果:
hello,world
None
练习2:自定义return返回值,return之后的语句将不再执行
- #!/usr/bin/env python
- def fun():
- print "hello,world"
- return "heihei"
- print "haha"
- print fun()
结果:
hello,world
heihei
练习3:判断输入是否为数字
函数里很少使用print,使用return,更加简化
- #!/usr/bin/env python
- import os
- def isNum(s):
- for i in s:
- if i not in "1234567890":
- return False
- return True
- for i in (os.listdir("/proc")):
- if isNum(i):
- print i
练习4:isdigit()判断输入是否为数字
isdigit():判断字符串是否为纯数字(脚本更更简化)
- #!/usr/bin/env python
- import os
- def isNum(s):
- if s.isdigit():
- return True
- return False
- for i in (os.listdir("/proc")):
- if isNum(i):
- print i
6.多类型传值(元组或字典)和冗余参数
一个元组只表示一个参数;元组加一个*,则可以把元组中的元素作为参数,传到脚本中;带参数的元组只能放在后面,否则有语法错误
练习1:
- In [2]: def fun(x,y,z):
- ...: print x + y +z
- ...:
- In [3]: a = [1,2]
- In [4]: fun(3,*a)
- 6
报错:
In [5]: fun(*a,3)
File "<ipython-input-5-8a9ea4381ff5>", line 1
fun(*a,3)
SyntaxError: only named arguments may follow *expression
练习2:
字典传参(形参名和实参名一致,位置无所谓)
- In [8] : def fun(x, y, z) : ...: print x + y + z...: In [9] : a = {
- "x": 1,
- "y": 2,
- "z": 3
- }
- In [10] : fun( * *a) 6
或者:
In [11]: fun(x=1,y=2,z=3)
6
练习3:
- In [1]: def fun(x,*argv,**kwargv):
- ...: print x
- ...: print argv
- ...: print kwargv
- ...:
- In [2]: fun(1)
- 1
- ()
- {}
练习4:
以等号或字典形式
- In [6]: def fun(x,*argv,**kwargv):
- ...: print x
- ...: print argv
- ...: print kwargv
- ...:
- In [7]: t = [1,2]
- In [8]: fun(1,2,"a",*t,y=1,**{"b":1,"c":2})
- 1
- (2, 'a', 1, 2)
- {'y': 1, 'c': 2, 'b': 1}
7.函数的递归调用(函数调用本身)
条件:
1)必须有最后的默认结果,即if n == 0
2)递归参数必须向默认结果收敛,即factorial(n-1)
练习:阶乘,n乘以f(n-1)
- #!/usr/bin/env python
- def factorial(n):
- if n == 0:
- return 1
- else:
- return n * factorial(n-1)
- print factorial(5)
结果:
120
练习2:累加,n加f(n-1)
- #!/usr/bin/env python
- def factorial(n):
- if n == 0:
- return 0
- else:
- return n + factorial(n-1)
- print factorial(5)
结果:
15
python—函数实例
来源: http://www.bubuko.com/infodetail-2414044.html