1.if语句
a = 10 b = 20 if(a>b): print("a max!") else: print("b max!")
b max!
student = "zhangxiaoyu" if (student == "zhanxgiaoyu"): print("YES") else: print("NO")
NO
if (student != "zhanxgiaoyu"): print("YES") else: print("NO")
YES 【in 和 not in 表示包含的关系】
hi = "hello python" if ("h" in hi): print("yes") else: print("no")
yes
if (" " in hi): print("yes") else: print("no")
yes
if ("i" in hi): print("yes") else: print("no")
no
【if语句可以进行布尔类型判断】
a = True if a: print(" a is True") else: print("a is no True")
a is True
2.for语句
names = ["xiaoyu","xiaowen","huahua","qiongge"] for name in names: print(name)
xiaoyu xiaowen huahua qiongge
for name in names: print(name) if(name == "huahua"): print("yes") break
xiaoyu xiaowen huahua yes
for name in names: print(name) if(name == "huahua"): print("yes") continue
xiaoyu xiaowen huahua yes qiongge
range()函数:默认从零开始循环,也可以设置起始位置和步长
for i in range(10): print(i)
01 2 3 4 5 6 7 8 9
for i in range(1,20,5): print(i)
1 6 11 16 3.数组与字典 (1)数组
lists = [1,2,3,4,5,6,'a'] lists[0] 1
lists[6] 'a'
lists[6] = 'n' lists[6] 'n'
lists.append("v") lists [1, 2, 3, 4, 5, 6, 'n', 'v'] (2)字典
ret = {"usenames":"xiaoyu","password":"12345"} ret.keys() dict_keys(['password', 'usenames'])
ret.values() dict_values(['12345', 'xiaoyu'])
ret.items() dict_items([('password', '12345'), ('usenames', 'xiaoyu')]) 4.函数、类和方法 (1)函数 def关键字来定义函数。
def add(a,b): print(a+b)
add(1,2) 3
sum = add(1,2) 3
def add(a,b): return (a+b)
add(1,9) 10
若在调用add()函数时不想传参,可设置默认参数。
def add(a = 1,b = 9): return (a+b)
add() 10
add(10,20) 30 (2)类和方法 class A(object): def add(self,a,b): return (a+b)
count = A() print(count.add(3,9))
class A(): def init(self,a,b): #初始化 self.a = int(a) self.b = int(b)
def add(self): return self.a+self.b
count = A(0,0) print(count.add()) class A(): #B继承A def add(self, a, b): return(a+b)
class B(A): def sub(self,a,b): return(a-b)
count = B() print(count.add(10,90)) print(count.sub(10-9,9)) 5.模组(类库、模块) (1)在time模块下面有一个ctime()方法用于获取当前时间 import time print(time.ctime())
from time import ctime #只会用到tiem下的ctime()方法 print(ctime())
import time print(time.ctime()) print(time.sleep(2)) print("休眠两秒") print(time.sleep(2)) print(time.ctime())
from time import * #“*”用于表示模块下面的所有方法 print(ctime()) print("休眠3秒") print(sleep(3)) print(ctime()) 5.异常 (1) try: open("abc.txt",'r') except FileNotFoundError: #试图打开一个不存在的文件与目录 print("异常了!") (2) try: print(aa) except NameError: #使用一个还未赋值对象的变量 print("这是一个name异常") (3) try: open("abc.txt",'r') print(aa) except Exception(BaseException) as msg: print("这是一个异常") print(msg) [Errno 2] No such file or directory: 'abc.txt' 在python中所有的异常类都继承Exception,所以可以使用它来接收所有类型的异常。从python2.5版本之后,所有的异常都有了新的基类BaseException。Exception同样继承自BaseException。 (4)异常与if语句配合 try: aa = "python" print(aa) except Exception as msg: print("有异常存在") else: print("输出正常,没有异常") try: aa = "python" print(aa) except Exception as meg: print(msg) finally: print("不管是否有异常存在,都会执行")