Python中乐高积木——函数

Posted 2020-10-20

一.函数的定义

def 函数名():
函数体
return 返回值1 返回值2
二.函数的调用
函数名()
实现答应返回值:print 函数名()
总结：
定义函数时,函数不执行
定义函数时，函数才执行
1.有参数的函数
(1)必选参数
#形式参数
def add(x,y)
print x + y
#实参，x=1,y=2
add(1, 2)

3

(2)默认参数
def mypow(x, y=2):
print x**y

mypow(2)

(3)可变函数
#形式参数
#args可以改为其他变量名；

def add(*args):
#args实质上是一个元组；

##print args
#        sum = 0
#        for i in args:
#                sum += i
#        print sum
 add(1, 2, 3, 4, 5, 6)

(4)关键字参数

#kwargs可以改为其他变量名；
#def inuser(name, age, **kwargs):
##kwargs实质上是一个字典；
#print name, age, kwargs
inuser("user1" 12 city="xi‘an" brith="20180102"
如果必选参数, 默认参数, > 可变参数, > 关键字参数
```;
(5)返回值
#函数中如果没有返回值return时,默认返回值None;

def add(x,y):
return x+y
print add(1,2)

3
None
#返回多个值
def fun(*args):
"""
返回最大值和最小值

:param args:
:return:
"""

#实质上python只能返回一个值;
#间接通过元组返回多个值;

return max(args), min(args)

print fun(23, 21, 1, 8,12)
/usr/bin/python2.7 /root/PycharmProjects/untitled/file/retu.py
(23, 1)

(5)函数作用域
1)global关键字必须先声明,再赋值;
#全局变量

num = 1
def fun():
num = 5
fun()
print num
1

num = 1
def fun():
global num #global声明num为全局变量
num = 5 #局部变量
fun()
print num
5

三.高级特性
1.切片
2.迭代
(1)是否可以for循环遍历的对象;
(2)isinstance判断是否可迭代;

In [1]: from collections import Iterable
In [2]: isinstance(‘hello‘, Iterable)
Out[2]: True

In [3]: isinstance([1, 2, 3, 4], Iterable)
Out[3]: True

In [4]: isinstance((1, 2, 3, 4), Iterable)
Out[4]: True

In [6]: isinstance({‘c‘:3, ‘d‘:4}, Iterable)
Out[6]: True

In [7]: isinstance({1, 2, 3}, Iterable)
Out[7]: True

![](http://i2.51cto.com/images/blog/201801/10/310edcd8cca1d532fb15e730c3d553ae.png?x-oss-process=image/watermark,size_16,text_QDUxQ1RP5Y2a5a6i,color_FFFFFF,t_100,g_se,x_10,y_10,shadow_90,type_ZmFuZ3poZW5naGVpdGk=)
四.列表生成式
(1)生成列表的公式

(2)需求:生成一个列表,返回1-100中偶数的平方;
[4, 16, 36......]

方法1:

li = []
for i in range(2,100,2):
...: li.append(i2)
...: print li
...:
[4, 16, 36, 64, 100, 144, 196, 256, 324, 400, 484, 576, 676, 784, 900, 1024, 1156, 1296, 1444, 1600, 1764, 1936, 2116, 2304, 2500, 2704, 2916, 3136, 3364, 3600, 3844, 4096, 4356, 4624, 4900, 5184, 5476, 5776, 6084, 6400, 6724, 7056, 7396, 7744, 8100, 8464, 8836, 9216, 9604]

方法2:
In [10]: [i2 for i in range(2, 10, 2)]
Out[10]: [4, 16, 36, 64]

![](http://i2.51cto.com/images/blog/201801/10/65d0356481e47384b351ac8a2855cd51.png?x-oss-process=image/watermark,size_16,text_QDUxQ1RP5Y2a5a6i,color_FFFFFF,t_100,g_se,x_10,y_10,shadow_90,type_ZmFuZ3poZW5naGVpdGk=)
(3)变异的列表生成式
#for循环嵌套for循环,两个字符串的全排列

In [12]: [i+j for i in ‘xyz‘ for j in ‘123‘ ]
Out[12]: [‘x1‘, ‘x2‘, ‘x3‘, ‘y1‘, ‘y2‘, ‘y3‘, ‘z1‘, ‘z2‘, ‘z3‘]

#for嵌套if语句

In [13]: [i**2 for i in range(2, 20, 2) if i%2==0]
Out[13]: [4, 16, 36, 64, 100, 144, 196, 256, 324]

应用:找出/etc下文件中以.conf结尾的文件;
提示:
    os.listdir("/etc")
    s.enswith(".conf")

In [14]: import os

In [17]: print [i for i in os.listdir(‘/etc‘) if i.endswith(‘.conf‘)],
[‘host.conf‘, ‘kdump.conf‘, ‘sysctl.conf‘, ‘ld.so.conf‘, ‘sestatus.conf‘, ‘nsswitch.conf‘, ‘nfsmount.conf‘, ‘man_db.conf‘, ‘libaudit.conf‘, ‘dnsmasq.conf‘, ‘request-key.conf‘, ‘krb5.conf‘, ‘dracut.conf‘, ‘libuser.conf‘, ‘rsyslog.conf‘, ‘logrotate.conf‘, ‘e2fsck.conf‘, ‘yum.conf‘, ‘mke2fs.conf‘, ‘idmapd.conf‘, ‘ovirt-guest-agent.conf‘, ‘rsyncd.conf‘, ‘chrony.conf‘, ‘sudo-ldap.conf‘, ‘sudo.conf‘, ‘vconsole.conf‘, ‘locale.conf‘, ‘resolv.conf‘, ‘grub.conf‘, ‘asound.conf‘, ‘fuse.conf‘, ‘colord.conf‘, ‘hba.conf‘, ‘sos.conf‘, ‘oddjobd.conf‘, ‘usb_modeswitch.conf‘, ‘ipsec.conf‘, ‘ksmtuned.conf‘, ‘mtools.conf‘, ‘radvd.conf‘, ‘numad.conf‘, ‘brltty.conf‘, ‘fprintd.conf‘, ‘wvdial.conf‘, ‘pbm2ppa.conf‘, ‘pnm2ppa.conf‘, ‘updatedb.conf‘, ‘lftp.conf‘, ‘Trolltech.conf‘]

![](http://i2.51cto.com/images/blog/201801/10/ec7cb73b20a5242bc0e9607652147fd9.png?x-oss-process=image/watermark,size_16,text_QDUxQ1RP5Y2a5a6i,color_FFFFFF,t_100,g_se,x_10,y_10,shadow_90,type_ZmFuZ3poZW5naGVpdGk=)

未完待续